If you have previously visited this website, this page allows you to see what information has been recently added or updated. This way, you do not have to search the entire site. The plan is to constantly add and update the website.

An automotive scan tool is an electronic device the technician uses to decode serial data, communicate with modules, diagnose problems, and sometimes reprogram vehicle control modules.

Remember that a scan tool is only as good as the user’s understanding of the data. When used with the proper reference materials, a scan tool can significantly help a knowledgeable, experienced technician performing computer-related diagnostics. Often, the device is more than a help; it's a necessity. But it cannot solve problems by itself. Understanding the data and accurately interpreting the information displayed is the key. The technician, not the tool, is the diagnostician.

Four Types of Scan Tools are available:

1. Code Readers – They are inexpensive and quick but might not provide all the Global MODEs.
2. Bluetooth for Smartphones – moderately priced but might not provide all the Global MODEs.
3. Aftermarket will display Global OBD II and Enhanced (OEM Level in most cases). 
4. OEM factory specific, but may not include any, or all, of the Global OBD II MODEs.

A scan tool can be Wired or Wireless (Bluetooth), handheld or PC-based. To achieve a higher level of diagnostics, a Global Code Reader or Bluetooth for IOS and Smartphones will not do the job.

Two options are available when using an aftermarket scan tool, technician and there are advantages to both:

Global (EOBD) OBD II: 

1. The system might not be identified by Make, Model, or Year (Note: Some Global Scan Tools can identify the vehicle based on the VIN). 
2. Talks in standard Protocols to all systems.
3. Pre-CAN PIDS can be limited. 
4. PIDS can be extensive and provide some PIDS the Aftermarket Enhanced scan tools do not provide. 
5. Provide many PIDS similar to Enhanced OBD II but may identify them using different terminology. 
6. It provides no bi-directional testing and can only command the EVAP Vent Solenoid On, if available.
7. It will communicate with emission-related modules like the Engine Control Module (ECM) and Transmission Control Module (TCM).

Aftermarket Enhanced (OEM) OBD II: 

1. Does identify the system by VIN, Make, Model, and Year. 
2. Talks using the protocol specific to the individual manufacturer. 
3. It provides many PIDS similar to Global but may identify them using different terminology. 
4. It might provide PIDS not found in Global OBD II. PIDS might be divided into pages. 
5. Provides Bi-Directional Testing of specific Outputs. 
6. It may provide reprogramming options.
7. Can communicate with most, if not all, modules on the vehicle.

Additional Scan Tool Features:

Combing an aftermarket Scan tool and online Service Information

The global scan tool can be combined with an online service information subscription. In the following video without audio, the INNOVA 7111 tablet will be combined with MOTOR Repair Service. Once a confirmed DTC triggers a MIL, the tool will link to MOTOR. There is a fee for accessing this online service. This video shows a first signup to MOTOR with a 30-day free trial. 

MORE INFORMATION TO BE ADDED SOON.

Pre and Post Scans

Network Topology Mapping

Secure Gateway - AUTO AUTH

Some aftermarket scan tools will display the Hexadecimal symbol ($), others will not.

Snap-On Global Scan Tool

AUTEL Global Scan Tool

A diagnostic trouble code (DTC) indicates that the enable criteria for a monitor test has failed outside of a minimum or maximum test limit. If the MIL is illuminated, tailpipe emissions have exceeded 1.5 times the Federal Test Procedure (FTP) standards. MODE $03 reports a DTC once the MIL is commanded ON. This can occur on the first or second consecutive trip. MODE $03 reports a DTC once the MIL is commanded ON. A DTC with the MIL ON is called a confirmed or current DTC. If the MIL is OFF and a DTC is still present, this is referred to as a history DTC. A history DTC remains in memory for 40 warmup cycles if the same code does not reoccur. It can also be cleared using a scan tool or by removing power from the ECM for a while. The length of time depends on the manufacturer. 

A five-digit alphanumeric code represents all DTCs. The first letter indicates the function of the monitored component or system that has failed:
P  =  Powertrain
B  =  Body
C  =  Chassis
U  =  Indicates a network or data link code

The second digit is represented by a number that indicates who is responsible for the code:
0  =  Society of Automotive Engineers (SAE)
1  =  Manufacturer specific

The third digit indicates the specific system in question. Numbers one through seven indicate a powertrain-related problem. The number eight is reserved for non-powertrain-related problems:
0  =  Total system
1  =  Air/Fuel metering control
2  =  Air/Fuel metering control for injector circuit malfunctions only.
3  =  Ignition system or misfire
4  =  Emissions Control
5  =  Vehicle Speed Control/Idle Control system
6  =  ECM and Computer Input/Output Circuits
7  =  Transmission
8  =  non-Powertrain related

The fourth and fifth digits represent the component, system, or area experiencing the problem.
DTC P0306 is described as:
P  =  Powertrain related
0  =  Manufacturer-defined DTC
3  =  Ignition system or misfire related problem
06  =  Cylinder #6 misfire detected. This MODE retrieves all stored emission-related DTCs from the PCM.

Types of Diagnostic Trouble Codes (DTC)

The ECM can set two kinds of DTC. 

1.  Functionality DTCs are related to electrical problems set by an open and short circuit. The image below demonstrates a functionality DTC.

2.  Rationality/Normality/Plausibility DTCs are performance-related problems. They are set by comparing similar inputs/outputs to see if they make sense. The customer's concern is loss of power under load. The image below shows three related PIDS: TPS, MAP, and RPM. In this case, the ECM must determine which of the three does not make sense. Can you identify the outlier PID that the ECM might flag as incorrect?

Live by codes, die by codes.  Sometimes, the ECM can be fooled because the reporting component is malfunctioning. The BARO and FTP PIDs must be checked KOEO and KOER to start an EVAP diagnosis. A DTC for an out-of-range sensor will not be set if the BARO or FTP reports in the yellow zone. This can lead to a false DTC, like a Large Leak because the FTP is not reporting the correct EVAP system pressure. If the BARO reports in this range, it could cause a driveability concern or the suspension of non-continuous readiness monitor tests.

More Content to be Added Soon!

MODE $05 - Oxygen Sensor Test Results

MODE $05 reports the latest Monitor Test results for the Oxygen Sensors. It is not “live” data. It is stored in memory and replaced with newer test results. The problem with this MODE is that not all manufacturers supported MODE $05. Also, this MODE did not allow the addition of Air Fuel Sensors.

Under CAN Regulations, MODE $05 was eliminated and moved to MODE $06.

MORE CONTENT TO BE ADDED, PLEASE CHECK BACK!

For most OBD II strategies, the same malfunction must occur on two driving events to illuminate the MIL. This “double” detection ensures a malfunction exists before alerting the owner. The first time a malfunction is detected, a “pending” fault code, which identifies the failing component or system, is stored in the onboard computer. If the same malfunction is again detected the next time the vehicle is operated, the MIL is illuminated, and a “confirmed” fault code is stored. When the MIL is illuminated (alerting the vehicle operator to a problem), and a vehicle is brought in for service, a technician uses the “confirmed” fault code to determine what system or component has failed. A “pending” fault code, however, can be used by service technicians to help diagnose intermittent problems and verify that repairs were successful. In these instances, a technician can use the “pending” fault code as a quicker, earlier warning of a suspected (but as yet unconfirmed) problem.

MORE CONTENT TO BE ADDED, PLEASE CHECK BACK!

Any confirmed DTC currently commanding the MIL On can set a Permanent Diagnostic Troubles Code (PDTC). They first appeared in 2010 as part of a three-year phase-in period. By the 2012 model year, all vehicles could set a PDTC. The ECM must have enough memory to store a minimum of four permanent DTCs. 

The following capture is an example of the three possible DTCs: a Pending DTC (MODE $07), a stored DTC (MODE $03), and a Permanent Diagnostic Trouble Code (MODE $0a). Note: This capture is from an AUTEL scan tool, which does not display MODEs using Hexadecimal symbols.

A PDTC (MODE $0a) will remain in memory after a stored DTC (MODE $03) is erased. This prevents someone from clearing a DTC before going for a state emissions test. This prevents a vehicle that would typically fail from passing. PDTCs are stored in a non-volatile RAM (NVRAM) to prevent them from being erased with the scan tool or by removing battery power from the ECM. 

A PDTC can only be erased from memory if the OBD system extinguishes the MIL (e.g., when the current DTC changes to a History DTC). If the memory is not cleared with a scan tool, the ECM must see the related monitor test complete and pass on three consecutive trips. The PDTC will not be removed from memory until the fourth key-on cycle. If the memory is cleared with the scan tool, the MIL will be extinguished; the MODE $03 (Confirmed DTC) and MODE $02 (FFD) will be cleared. The PDTC will still be in memory, but it will take only one good trip and a second key-on cycle to remove it from memory. 

If multiple PDTCs are present, clearing them from memory could take many trips and miles. If the stored MODE $03 DTC is no longer present, this should not affect driveability or emissions. Clearing a Permanent Diagnostic Trouble Code was initially complicated. Eventually, these issues were resolved by reprogramming the ECM. If a reflash update is designed to fix a PDTC issue, the PDTC will be erased during the update. If the reflash is unrelated to the PDTC, the update cannot erase it.

For a Misfire and Fuel System PDTC, the ECM must support storing up to four similar conditions window (SCW) in NVRAM to allow proper clearing from memory. If a Misfire of Fuel System PDTC is stored during the first occurrence, the ECM must store an SCW that includes engine speed +/- 375 rpm, engine load +/-20 %, and the same warmup condition below 160°F or 160°F and above. The SCW allows the ECM to monitor the specific Misfire/Fuel system conditions when the DTC was initially set. If additional Misfire or Fuel System DTCs are specified, each must store a SCW.

Think of an SCW as a freeze frame set in memory when a Pending DTC (MODE $07) is set for a misfire or fuel system problem. It gives the ECM the window of information it needs to monitor a recurrence under the same driving conditions. The technician cannot view this information when a Pending DTC is present. If a second failure and a confirmed DTC is set in the same window, the MIL will be ON, and a reviewable freeze frame will be stored in MODE $02. Now, the technician can review the conditions that set the DTC through the freeze frame data (FFD). 

Chrysler is the only manufacturer that provides this information through its factory scan tool. The following two captures demonstrate Similar Conditions Windows (SCW). 

For Smog Inspectors in California, pay attention to Warmup cycles and Miles Driven.  PID $30 (Warm-up Cycles Since Cleared) and PID $31 (Distance Traveled Since Cleared) are used by the OIS to Pass or Fail a vehicle with a PDTC(s). If the Warm-Up Cycles are 14 or less or the Distance Traveled is less than 200 miles, the OIS will fail the vehicle. If the Warm-Up Cycle counter is => 15 and the Distance Traveled is => 200 miles, the OIS will ignore the PDTC and pass this inspection portion.

For 2010MY and newer, the California Air Resources Board (CARB) created a universal drive cycle pattern for clearing misfire and fuel systems DTCs. Before this type of PDTC can be erased, Cumulative time since engine start must be 600 seconds; Cumulative vehicle operation at or above 25 miles per hour equal to 300 seconds (medium-duty vehicles with diesel engines certified on an engine dynamometer may use cumulative operation at or above 15% calculated load instead of the 25 miles per hour); and Continuous vehicle operation at idle (i.e., accelerator pedal released by driver and vehicle speed less than or equal to one mile per hour) for greater than or equal to 30 seconds. Then, the ignition must be turned off for at least five seconds and then cycled on again.

The California Smog Check Program is the only state that uses Permanent Diagnostic Trouble Codes to fail a vehicle. There are some exemptions to this rule, and they can be found at On-Board Diagnostic Test Reference - Bureau of Automotive Repair.

Topics in this section include:

1. Drive Cycle Pattern 1
2. Drive Cycle Procedures
3. Drive Cycle Video

1. This pattern should be used for most 1996-2007 Chrysler and Dodge vehicles. The differences within this pattern are the methods of EVAP Leak Detection.  The system will test after a cold soak start if it has a leak detection pump (LDP). If it has a Natural Vacuum Leak Detection (NVLD) or EVAP System Integrity Module (ESIM) switch, it will test after the end is shut off.

2. The procedure listed pertains to the pattern shown above. NOTE: These steps can run out of order depending on the vehicle speed and engine load.

3. The video was captured while performing the drive cycle on a dynamometer.  The factory scan tool was used to display the inner workings of the Engine Control Module (ECM).  Note: The enable criteria are shown on the scan tool at the top of each screen.  The readiness flag status for this drive cycle is displayed in the middle of the screen.

This drive cycle has been used for many FORD vehicles since 1998. One important note is that it does not mention the O2 Sensor monitor test. Experience has proven that O2 heaters and O2 readiness flags work together. The O2 heater must run and pass before the O2 monitor test will run and flip the readiness flag to Complete! 

Note: for Ford vehicles equipped with Universal Exhaust Gas Sensors (UEGO), a variation of the HEGO step listed below is required. This is covered later in this section. 

Some Ford products have an EVAP Monitor Cold Soak Bypass Timer. An internal timer in the ECM determines Cold Soak. If available, it will be displayed on the OEM side of the scan tool under Current Data/Emissions. If the status is YES, the vehicle has sat long enough to achieve a Cold Soak, allowing the EVAP monitor test to run if the fuel level is correct. If it says No, it is not ready, but it can be bypassed. To Bypass the EVAP Monitor Soak Time Command, turn the key on with the engine off and perform a MODE $04 Diagnostic Clear, but do not turn the key off. The Cold Soak Bypass Timer will switch from NO to YES. After clearing the information, do not turn the key off; start the engine and follow the abovementioned steps. It is now ready to run the EVAP monitor tests, allowing other monitor's tests to run, providing their enable criteria are met.

The Cold Soak Bypass timer is not available on all Ford vehicles. The only way to be sure is to check the emissions page through the enhanced side of the scan tool.

Topics in this section include:

1. Drive Cycle Pattern
2. Drive Cycle Procedures
3. Drive Cycle without EVAP Video
4. Drive Cycle EVAP Video

1. This pattern was used for most NISSAN/INFINITI between 2004 & later vehicles.  The EVAP system will be tested under a vacuum in Steps 4 & 5 during these years. If the Fuel Tank Temperature Sensor indicates the fuel tank temperature has not increased enough, step 6 must be performed.

2. The steps listed pertain to the pattern shown above. NOTE: Depending on the startup engine temperature, vehicle speed, and engine load, these steps can run out of order.

3. This video was captured while performing the drive cycle on a dynamometer.  The factory scan tool at that time displayed the inner workings of the Engine Control Module (ECM). NISSAN Pattern 2 was used for most NISSAN/INFINITI vehicles after 1998.  The main difference after 2003 was with the EVAP system.  The video does not show Steps 5 & 6 in Pattern 2.  Those steps will be shown in the following video.

4. This video shows NISSAN Pattern Steps 4 - 5.  Step 6 is only required if the Fuel Temp Sensor does not rise a minimum of 4⁰ F (2⁰ C).  Performing step 6 multiple times will slosh the fuel in the tank, increasing temperature and pressure. Focus your attention on the Purge VOL and Vent solenoids.  This system leaks, so the PCM first tests the system using vacuum decay and then proceeds to test the system under pressure.

Topics in this section include:

1. Drive Cycle Pattern
2. Drive Cycle Procedures
3. Drive Cycle without EVAP video
4. Drive Cycle non-Intrusive EVAP video

1. This pattern should be used for 1996-2000 Toyota and Lexus vehicles. These vehicles were equipped with a non-Intrusive Evaporative Emission System.

2. The steps listed pertain to the pattern shown above. NOTE: Depending on the startup engine temperature, vehicle speed, and engine load, these steps can run out of order.

3. This video was captured while performing the drive cycle on a dynamometer.  The factory scan tool at that time displayed the inner workings of the Engine Control Module (ECM).

4. This video shows the non-Intrusive EVAP monitor tests running to completion at steady cruise after a Cold Soak startup.  While watching the video, look closely at the PIDs (Purge, Vapor Pressure, and Vapor Pressure Solenoid); they monitor the system for leaks. Note:  The readiness flag status for this drive cycle is displayed at the bottom of the screen.

This section will address some oddities when performing individual monitor tests, separate from running a complete drive cycle.

MORE CONTENT TO BE ADDED; PLEASE CHECK BACK!

In-Use Monitor Performance Tracking (IUMPT) - CASE STUDY

Evaporative emission systems (EVAP) have been used as an anti-pollution system on most 1970 light-duty vehicles sold in California. Some medium/heavy-duty and 4x4 vehicles had later deadlines.  Starting in 1971, all Federal/USEPA vehicles (forty-nine states) were required to be equipped with some evaporative emission system. EVAP regulations prohibited uncontrolled hydrocarbons from entering the atmosphere from the evaporative emission system.    

Evaporative emission systems trap, store, and release gasoline vapors into the engine to mix with the incoming air/fuel mixture.  These gasoline vapors are also called volatile organic compounds (VOCs). Volatile organic compounds are those parts of a fuel’s composition that contribute to photochemical smog when introduced into the atmosphere. 

Over 20% of the hydrocarbons a motor vehicle generates result from fuel evaporation when the engine is not running.  Hydrocarbon emissions caused by evaporative emissions can be defined as follows: 

1.    Diurnal Loss: Vapors vent to the charcoal canister as the ambient temperature rises during the day.  Excess vapors will enter the atmosphere if the charcoal canister reaches a saturation point.  Diurnal loss is measured with the engine off and usually occurs within 35 minutes of shutdown. 

2.    Hot Soak: The engine remains hot long after the vehicle has been turned off.  For 35 minutes, emissions are measured to gauge this event.  Evaporation occurs from fuel that has been heated in the engine compartment and all fuel supply and vent lines.   

3.    Resting Loss: Gasoline permeates rubber and plastic components in the fuel system while the vehicle is at rest.  This event occurs when the vehicle has been turned off and allowed to sit for at least thirty-five minutes in a steady or decreasing ambient temperature condition. 

4.    Running Loss: Gasoline vaporizes as the engine is running.  The running loss test is conducted in an enclosure on a dynamometer.  The exhaust gases are routed out of the enclosure, leaving only vapors from evaporation.  The running loss test occurs over one hour while the vehicle is driven through three consecutive Federal Test Procedure (FTP) drive cycles.           

The EPA has devised the Sealed Housing Evaporative Determination Test (SHED).  All evaporative hydrocarbon emissions from fuel, tires, and plastics are collected and measured during this test.  This test includes a multi-day Diurnal Test (Enhanced Evaporative Emission Test), where the vehicle is repeatedly heated and cooled to simulate the effects of hot and cold ambient temperatures.  The figure below shows a drawing of the SHED setup. Courtesy of Colorado State University-NCVECS           

Factory emission tests have determined that an EVAP system with a leak as small as .020 inch can yield an average of 1.35 grams of hydrocarbons per vehicle per driven mile.  This is over thirty times the current allowable exhaust emissions standard. Evaporative System Operation  The Evaporative Emission Control (EVAP) system is designed to store and dispose of fuel vapors usually created in the fuel system, preventing its escape to the atmosphere.  The EVAP system delivers these vapors to the intake manifold to be burned with the usual air/fuel mixture.  This fuel charge is added during periods of closed-loop operation when the closed-loop fuel control system can manage the additional enrichment.  Improper operation of the EVAP system may cause rich driveability problems and failure of the Two-Speed-Idle test or Enhanced I/M loaded mode ASM test. The EVAP system is a fully closed system designed to maintain stable fuel tank pressure without allowing fuel vapors to escape into the atmosphere.  Fuel vapor is usually created in the fuel tank due to evaporation.  It is then transferred to the EVAP system charcoal canister when tank vapor pressures become excessive.  The canister absorbs fuel vapors until it becomes fully saturated.  When engine operating conditions can tolerate additional enrichment, these stored fuel vapors are purged into the intake manifold and added to the incoming air/fuel mixture. 

Types of Evaporative Emission Systems        

Identifying the type of EVAP system equipped on the vehicle is essential.  Since 1970, several methods have been used.  The following are the most common: 

1.    Non-ECM-controlled EVAP systems use solely mechanical means to collect and purge stored fuel vapors.  Typically, these systems use a ported vacuum purge port and a Thermo or Ported Vacuum Switch to prohibit system operation during a cold start or warm-up. 

2.  Pre-OBD II ECM Controlled EVAP systems use a ported or intake manifold vacuum purge source with a duty-cycled vacuum switching solenoid.  This type of EVAP system can provide more precise control of purge-flow volume and operation inhibition.  It cannot check the system for leaks.  Sometimes, the ECM does not know if purge flow occurred. 

3.    OBD II systems will be seen in either Non-Enhanced or Enhanced form.  This book will address these two systems: 

A)  Non-enhanced systems can only detect purge flow but cannot check the system for leaks.  These systems do not include a readiness monitor. They were installed on some 1996 and 1997 model-year vehicles.  

B)   Enhanced systems can detect purge flow and system leaks by using vacuum switches or pressure sensors.  A vent solenoid, vent valve, or closed canister valve can identify them.  Some systems test when the key is turned off.  All systems include a readiness monitor. Enhanced EVAP has required equipment on all 1998 and newer model-year vehicles. Enhanced EVAP systems can be divided into various types that accomplish the same goal using different methods.  Depending on the model year, enhanced evaporative emission systems must be capable of identifying leaks as small as .040 inch or .020 inch.  These systems perform the test by either lowering the pressure, thus creating a vacuum, or increasing the pressure through a pump. 

Methods of Testing Enhanced Evaporative Emission Systems 

1.    Vacuum Decay:  The vacuum method utilizes a purge solenoid, vent solenoid, or close canister valve (CCV) and a fuel tank pressure sensor (FTP).  These components monitor the evaporative emission system for leaks.  This system uses an engine vacuum through the purge solenoid to create a vacuum in the closed system.  This is the most common system in use today. 

2.    Fuel Tank Pressure/Canister Vacuum: This system has been used by Honda and Toyota and can isolate the fuel tank from the charcoal canister to pinpoint the leak.  Toyota utilizes two versions of this system: a non-intrusive system, which was used from 1996-2002, the second is called an intrusive system, which was introduced in 2000.  

3.    Leak Detection Pump: This system pressurizes or creates a vacuum in the evaporative emission system through a leak detection pump (LDP).  LDP has been used by Audi, BMW, Chrysler, Hyundai, Mitsubishi (Chrysler products), Volkswagen, and Volvo.  In 2000, BMW, Hyundai, and Mazda introduced a Diagnostic Module for Tank Leakage (DM-TL) pump to pressurize the system with the engine off.  Toyota 2005 introduced a vacuum pump module key-off system. 

4.    Engine off Natural Vacuum Leak:  This system works on the fluid’s vacuum/pressure principle in a closed container.  As temperature increases - the pressure increases if no leaks are present.  This system primarily tests for a very small leak (.020”).  It first appeared in 2002 model year vehicles, and Chrysler, Ford, GM, and Honda use variations of this system. To inspect or repair these systems, the technician must be able to identify them.

Even though the EVAP system performed well, it could not control the hydrocarbons escaping during refueling.  Starting in 1998, vehicles were required to have an On-board Re-fueling and Vapor Recovery (ORVR).  The vapor return systems installed on gas pump nozzles had relatively little effect on the amount of vapor escaping.         

As a result, the ORVR system was created to trap the hydrocarbons released during refueling.  An ORVR system was designed to control vapors produced during refueling by routing them to the canister during fuel refill.         

As fuel is channeled into the Fuel Tank, the ORVR system directs the fuel vapor to be stored in the EVAP Canister.  This vapor is later routed to the engine to be burned during normal combustion. The EVAP and ORVR systems have been very successful in the containment of hydrocarbon emissions.        

To see how this is accomplished, let’s first take a look at the components in the system: The ORVR system can consist of the following: 

1.  Fuel Filler Neck:  The filler neck on many models consists of the main pipe for the fuel delivery into the tank, the one or smaller lines that help control fuel vapor flow, and tank overflow control.  The ORVR fuel filler neck is designed to make a dynamic liquid seal, dispensing fuel from the fuel nozzle.  The smaller diameter filler neck creates suction around the fill neck opening. It draws air and any escaping vapors into the filler neck to be pushed into the tank during refueling. 

2.  Fuel Shut-Off (Fuel Cut) Valve: The fuel cut valve (anti-spit back) valve prevents fuel from splashing back up the filler neck. The spring-loaded valve opens automatically when refueling.  The force of the fuel flowing is enough to open the valve when refueling. 

3.  Fill Vent Valve: The fill vent valve controls the flow of vapors during refueling. The valve is open when the tank is near empty.  As fuel enters the tank, the vapors flow into the charcoal canister through the fill vent valve.  A float in the valve rises as the fuel level approaches the full point. When the tank is full, the valve is closed to prevent liquid fuel from going through the valve. 

4.  Fuel Rollover Valve: The primary purpose of the rollover valve is to allow vapors to flow from the fuel tank to the charcoal canister.  When the vehicle is parked on a steep incline, the valve is closed to prevent fuel spillage from the fuel tank into the charcoal canister.  In the event of a vehicle rollover, it keeps liquid fuel out of the EVAP canister. 

5.  Fuel Liquid/Vapor Separator: The liquid-vapor separator prevents liquid fuel droplets from reaching the vapor canister. A barrier inside the separator allows vapor to travel freely, but fuel droplets are too heavy and trapped. The droplets either travel back into the fuel tank or vaporize and are stored in the charcoal canister. 

6.  Two-Way Valve for Pressure/Vacuum Relief: The two-way valve is a directional valve that allows fresh air into the charcoal canister.  The valve also acts as a pressure relief valve if the system pressure gets too high.  The arrow on the valve points toward the charcoal canister.  When testing this valve, air should pass easily in one direction, and airflow should be somewhat restricted in the other direction.  When replacing this valve, refer to the system diagram for the correct installation.  The arrow on the valve indicates the direction of airflow.  This valve must be installed in the right direction. 

7.  Hoses, Pipes, and Gaskets: The hoses, pipes, and clamping devices are critical to proper ORVR operation.  Misrouted, damaged, or disconnected hoses can cause various symptoms, including difficulty filling the fuel tank with fuel or the MIL light coming “ON” for an evaporative system leak Diagnostic Trouble Code (DTC). 

8.  Charcoal Canister: The charcoal canister stores fuel vapors.  The canister contains activated charcoal.  During refueling, the charcoal can absorb fuel vapors, cleaning the vapor mixture and allowing uncontaminated air to escape into the atmosphere.  Fresh air drawn into the canister during purging releases the fuel vapors and recharges the charcoal.  Details of this are covered in the evaporative system components section.        

These components work together with the ECM to prevent fuel vapor from escaping and route it to the intake manifold to be burned during normal combustion.  Either through heat or agitation, fuel vapor builds up inside the Fuel Tank.         

The fill pipe diameter reduces after the unleaded restrictor plate. This restricted pipe size forms a liquid seal into the tank rather than letting fumes escape. The check valve is spring-loaded to prevent fuel from entering the filler pipe.        During refueling, a small amount of air is drawn into the filler pipe to prevent fuel vapors from escaping into the air during refueling. These vapors are drawn into the fuel nozzle and returned to the station’s tank.        

The vapor valve vents to the canister through the ORVR valve, which has a float to close off the vent when the tank is full.  A faulty ORVR valve can leak or cause difficulty when filling the tank, as pressure builds and causes early shut off of the filler nozzle.  Both valves shut off during a rollover event.        

The ORVR valve may have a pressure relief valve, spring loaded in both directions for zero pressure in the tank and zero vacuum, that is vented to the atmosphere. A buzzing noise may be heard in hot weather conditions just as the engine is turned off. This is because the tank is being sealed under low pressure.        

The primary purpose of this system is to route the fuel vapors that may escape from the filler neck during vehicle refueling into the EVAP canister. The canister absorbs these vapors and then purges them during driving. 

Operation  As the tank is refueled, a slight vacuum is created in the Signal Line by moving fuel at the top of the filler neck. This vacuum signal is applied to the top of the Refueling Control Valve by the Signal Line, which opens the Refueling Control Valve.        The fuel entering the fuel tank creates a slight positive pressure in the tank, which causes the EVAP Vapor Cut Valve to open.  With the Refueling Control Valve and EVAP Vapor Cut Valve open, fuel vapor can travel directly from the tank to the EVAP canister via the Refueling EVAP Vapor Line.  The Recirculation Line minimizes the amount of fresh air pulled into the tank by recirculating the air in the tank, to the filler neck, and back to the tank. 

Troubleshooting Most concerns about the ORVR system will be "slow-fill" concerns. A faulty ORVR valve can leak or cause difficulty when filling the tank, as pressure builds and causes early shut off of the filler nozzle.  Some owners may experience difficulty 'filling their vehicles with gasoline and a premature shut-off condition due to the gas pump nozzles installed at their gas stations. The nozzles at these stations are in the process of being retrofitted or replaced by the nozzle manufacturers. In the meantime, owners should follow instructions posted near the gas pump and try filling the vehicle at a different gas station. If the refueling difficulty continues, verify that the 1/2" vapor path from the fill vent valve on the gas tank to the air filter on the charcoal canister is entirely free and clear. To perform the procedure below, ensure the fuel tank is below 1/4 tank full. To quickly determine the general location of a possible vapor path restriction, Disconnect the hose connected to the canister side of the liquid-vapor separator. Take the vehicle to a known "good" or major brand gas station. A. If the vehicle accepts fuel, the restriction is between the liquid-vapor separator and the air filter. B. The restriction is located between the liquid-vapor separator and the fuel tank if the vehicle does not readily accept fuel. After the restriction has been isolated to either half of the system, inspect each component to ensure it is free and clear of any restrictions. Verify that no back pressure can be felt anywhere between the fill vent valve and the air filter at the canister. All hoses and tubes for the ORVR System must be free and clear for proper operation.  The ORVR lines are part of the EVAP system, so don't overlook them when diagnosing an EVAP leak concern.  Blow through one end of the pipe using lung power when checking the liquid-vapor separator. NO back pressure should be felt. Please verify that the Fill Vent Valve is open by carefully removing the valve and confirming that the white plastic shut-off plunger moves freely inside its cage. A hard-to-fill condition may result if the Fuel Cut Valve plunger is stuck closed.  Verify that the plunger moves up and down freely, allowing fuel to enter the tank but does not allow fuel to travel up the neck (under pressure).  The plunger should be "up" (closed) in its free state. When working with the Fill Vent Valve and associated plumbing, replace the hoses with the proper hose clips to prevent fuel from getting trapped/puddled in the vapor hose. Return fuel from the liquid-vapor separator must have a clear path to drain back to the tank. Related DTCs: P0442 Small Leak P0456 Very Small Leak

• Apply (opencccapply.net)
• When completing the application, you will be asked about your Educational Goals.  Check non-degree and maintain a Certificate or License (Upgrading your Skills).  Selecting any other options will refer you to a counselor, holding up your registration.
• Please add a cell phone and regular email address to your account.
• Usually, but not always, within 24 hours, they will send you an email allowing you to register.
• Once in WEBSMART, select Student Services, Registration Add/Drop, Fall 2024 Semester.
• Upcoming ONLINE Fall 2024 Smog Check Update classes:
  • December 7/8, the class Course Reference Number (CRN) is 98324.
• Online Spring 2025 Smog Check Update Classes:
  • February 22/23, the class Course Reference Number (CRN) is 48647
  • May 10/11, the class Course Reference Number (CRN) is 48648
• After processing the application, they will have you create a WebSmart login. Please change your educational goal in WebSmart to “Improve job skills or self-development” to exempt you from orientation, assessment, and counseling.
• Pay your fees. 
• I will send you specific information about the course and the materials before the start of the class.

If you have any questions, email me at escalambre@smccd.edu.

Rick Escalambre explores Global OBD (onboard diagnostics) and introduces OBD on Unified Diagnostic Services (OBDonUDS). The first OBDonUDS vehicle was recently released. By 2027, all light—and medium-duty vehicles will be equipped with this new generation of OBD systems.

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