Engine Control System - 4.8l, 5.3l & 6.0l (Troubleshooting) Chevrolet Chevy Express G2500

Important Preliminary Inspections Before Starting

Perform Diagnostic System Check - Engine Controls before using the symptom tables, and verify that all of the following are true

1. The powertrain control module (PCM) and malfunction indicator lamp (MIL) are operating correctly.
2. There are no DTCs stored.
3. The scan tool data is within the normal operating range, refer to «Scan Tool Data List»(/chevrolet/chevy-express-g2500/1996-2012/remont/door-locks-anti-theft-systems/#theft-deterrent-system__scan-tool-data-list) .
4. Verify the customer concern and locate the correct symptom in the table of contents. Inspect the items indicated under that symptom.

Visual/Physical Inspection

Several of the symptom procedures ask for a careful visual and physical inspection. This step is extremely important. The visual and physical inspection can lead to correcting a problem without further inspections, and can save valuable time. Ensure that

1. The PCM grounds are clean, tight, and in the proper location.
2. The vacuum hoses are not split or kinked, and properly connected, as shown on the Vehicle Emission Control Information label. Inspect thoroughly for any type of leak or restriction.
3. The mass air flow (MAF) sensor is properly installed. The arrows on the plastic portion of the sensor must point toward the engine.
4. The air intake ducts are not collapsed or damaged.
5. There are no leaks at the throttle body mounting area, the MAF sensor, or the intake manifold sealing surfaces.
6. The ignition wires are not cracked, brittle, or carbon tracked.
7. The engine harness wiring and terminals are properly connected and are not pinched or cut.

Intermittent

Faulty electrical connections or wiring cause most intermittent problems. Perform a careful visual and physical inspection of the suspect connectors for the following conditions

1. Improperly mated connector halves
2. Terminals that are not seated
3. Terminals that are damaged or improperly formed

Reform or replace connector terminals in the problem circuit in order to ensure proper contact tension. Refer to Connector Repairs in Wiring Systems. Remove the terminal from the connector body in order to inspect for poor terminal wire connection. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Road test the vehicle with the DMM connected to the suspected circuit. An abnormal reading that occurs when the malfunction occurs is a good indication that there is a malfunction in the circuit being monitored.

Use a scan tool in order to help detect intermittent conditions. Useful features of the GM Techline scan tool include the following

1. Trigger the Snapshot feature in order to capture and store engine parameters when the malfunction occurs. Review this stored information in order to see the specific running conditions that caused the malfunction.
2. Freeze Frame/Failure Records can also aid in locating an intermittent condition. Review and capture the information in the Freeze Frame/Failure Record associated with the intermittent DTC being diagnosed. Drive the vehicle within the conditions that were present when the DTC originally set.
3. Use the Plot Function on the scan tool in order to plot selected data parameters. Review this stored information to aid in locating an intermittent problem. Refer to the scan tool Users Guide for more information.

Any of the following may cause an intermittent malfunction indicator lamp (MIL) with no stored DTC

1. The ignition coils are shorted to a ground or arcing at the ignition wires or the spark plugs.
2. The PCM grounds are loose or dirty. Refer to «Engine Controls Schematics»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-introduction) .
3. The ignition control (IC) wires are routed too close to the secondary ignition wires, coils, or the generator. Ensure that all of the circuits from the PCM to the ignition coils have good connections.
4. There is an open diode across the A/C compressor clutch or any other open diodes.

Use the following tables when diagnosing a symptom complaint

1. «Intermittent Conditions»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__intermittent-conditions)
2. «Hard Start»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__hard-start)
3. «Surges/Chuggles»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__surgeschuggles)
4. «Lack of Power, Sluggishness, or Sponginess»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__lack-of-power-sluggishness-or-sponginess)
5. «Detonation/Spark Knock»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__detonationspark-knock)
6. «Hesitation, Sag, Stumble»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__hesitation-sag-stumble)
7. «Cuts Out, Misses»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__cuts-out-misses)
8. «Poor Fuel Economy»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__poor-fuel-economy)
9. «Poor Fuel Fill Quality»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__poor-fuel-fill-quality)
10. «Rough, Unstable, or Incorrect Idle and Stalling»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__rough-unstable-or-incorrect-idle-and)
11. «Dieseling, Run-On»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__dieseling-run-on)
12. «Backfire»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__backfire)

Intermittent Conditions

Intermittent Conditions

Hard Start

Hard Start

Surges/Chuggles

Surges/Chuggles

Lack of Power, Sluggishness, or Sponginess

Lack of Power, Sluggishness, or Sponginess

Detonation/Spark Knock

Detonation/Spark Knock

Hesitation, Sag, Stumble

Hesitation, Sag, Stumble

Cuts Out, Misses

Cuts Out, Misses

Poor Fuel Economy

Poor Fuel Economy

Poor Fuel Fill Quality

Poor Fuel Fill Quality

Rough, Unstable, or Incorrect Idle and Stalling

Rough, Unstable, or Incorrect Idle and Stalling

Dieseling, Run-On

Dieseling, Run-On

Backfire

Backfire

Circuit Description

Battery positive voltage is supplied directly to the malfunction indicator lamp (MIL). The powertrain control module (PCM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.

MIL Operation

The MIL is located on the instrument panel cluster (IPC).

MIL Function

1. The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible.
2. The MIL illuminates during a bulb test and a system test.
3. A DTC will be stored if a MIL is requested by the PCM.

MIL Illumination

1. The MIL will illuminate with ignition switch ON and the engine not running.
2. The MIL will turn OFF when the engine is started.
3. The MIL will remain ON if the self-diagnostic system has detected a malfunction.
4. The MIL may turn OFF if the malfunction is not present.
5. If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated so long as the ignition switch is ON.
6. If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.

Test Description

The number below refers to the step number on the diagnostic table.

1. 4: This step tests for a short to voltage on the MIL control circuit. With the fuse removed there should be no voltage on the MIL control circuit.

Malfunction Indicator Lamp (MIL) Inoperative

Battery positive voltage is supplied directly to the malfunction indicator lamp (MIL). The powertrain control module (PCM) turns the MIL ON by grounding the MIL control circuit.

The MIL is located on the instrument panel (IPC).

MIL Function

1. The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible.
2. The MIL illuminates during a bulb test and a system test.
3. A DTC will be stored if a MIL is requested by the diagnostic.

MIL Illumination

1. The MIL will illuminate with ignition switch ON and the engine not running.
2. The MIL will turn OFF when the engine is started.
3. The MIL will remain ON if the self-diagnostic system has detected a malfunction.
4. The MIL may turn OFF if the malfunction is not present.
5. If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated so long as the ignition switch is ON.
6. If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.

Diagnostic Aids

If the problem is intermittent, refer to Intermittent Conditions .

The number below refers to the step number on the diagnostic table.

1. 2: This step determines if the condition is with the MIL control circuit or the PCM.

Malfunction Indicator Lamp (MIL) Always On

Description

The Engine Cranks but Does Not Run diagnostic table is an organized approach to identifying a condition that prevents an engine from starting. The Engine Cranks but Does Not Run diagnostic table directs the service technician to the appropriate system diagnosis.

The Engine Cranks but Does Not Run diagnostic table assumes the following

1. The battery is completely charged. Refer to «Battery Inspection/Test (Non-HP2)»(/chevrolet/chevy-express-g2500/1996-2012/remont/charging-system/#battery-charging-system-and-starting-system) in Engine Electrical.
2. The cranking speed is acceptable. Refer to «Engine Cranks Slowly»(/chevrolet/chevy-express-g2500/1996-2012/remont/charging-system/#battery-charging-system-and-starting-system__engine-cranks-slowly) in Engine Electrical.
3. There is adequate fuel in the fuel tank.

Engine Cranks but Does Not Run

The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within two seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within two seconds if ignition reference pulses cease to be detected and the ignition remains ON.

A fuel pump prime terminal is located at the underhood bussed electrical center (UBEC). Refer to the UBEC cover for terminal location.

The following conditions may have caused the fuel pump fuse to open

1. A faulty fuse
2. An intermittent short in the fuel pump power supply circuit
3. An intermittent internal component failure

For an intermittent condition, refer to Intermittent Conditions .

The numbers below refer to the step numbers on the diagnostic table.

1. 3: This step determines if the condition is located on the coil side or on the switch side of the fuel pump relay.
2. 4: This step verifies that the powertrain control module (PCM) is providing voltage to the fuel pump relay.
3. 5: This step tests for an open in the ground circuit to the fuel pump relay.
4. 6: This step determines if a voltage is constantly being applied to the fuel pump relay.
5. 13: This step determines if the condition with the circuit is intermittent.

Fuel Pump Electrical Circuit Diagnosis

System Description

The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within two seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within two seconds if ignition reference pulses cease to be detected and the ignition remains ON.

The Fuel System is a returnless on-demand design. The fuel pressure regulator is a part of the fuel sender assembly, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.

The fuel tank stores the fuel supply. An electric turbine style fuel pump attaches to the fuel sender assembly inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel sender assembly. The function of the venturi pump is to fill the fuel sender assembly reservoir. The fuel pressure regulator, a part of the fuel sender assembly, maintains the correct fuel pressure to the fuel injection system. The fuel pump and sender assembly contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.

Fuel System Diagnosis

The control module enables the appropriate fuel injector pulse for each cylinder. Ignition voltage is supplied directly to the fuel injectors. The control module controls each fuel injector by grounding the control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high or too low will affect engine driveability. A fuel injector control circuit DTC may not set, but a misfire may be apparent. The fuel injector coil windings are affected by temperature. The resistance of the fuel injector coil windings will increase as the temperature of the fuel injector increases.

1. The use of Dielectric compound GM P/N 12377900 (Canadian P/N 10953529) in the fuel injector electrical connector may eliminate a corrosion condition.
2. Monitoring the misfire current counters, or misfire graph, may help isolate the fuel injector that is causing the condition.
3. Operating the vehicle over a wide temperature range may help isolate the fuel injector that is causing the condition.
4. Perform the fuel injector coil test within the conditions of the customers concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.
5. If the fuel injector coil test does not isolate the condition perform the fuel injector balance test. Refer to «Fuel Injector Balance Test with Special Tool»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting) or «Fuel Injector Balance Test with Tech 2»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting) .

Fuel Injector Coil Test

The scan tool is first used to energize the fuel pump. The fuel injector tester is then used to pulse each injector for a precise amount of time, allowing a measured amount of fuel into the manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each injector.

Scheme 140

Fuel Injector Balance Test Example (Typical)

The numbers below refer to the step numbers on the diagnostic table.

1. 6: If the pressure drop value for each fuel injector is within 10 kPa (1.5 psi) of the average pressure drop value, the fuel injectors are flowing properly. Calculate the pressure drop value for each fuel injector by subtracting the second pressure reading from the first pressure reading. Refer to the illustration above.

Fuel Injector Balance Test with Special Tool

The scan tool is first used to energize the fuel pump. The scan tool is then used to pulse each injector for a precise amount of time, allowing a measured amount of fuel into the manifold. This causes a drop in system fuel pressure that can be recorded and used to compare the flow through each injector.

Fuel Injector Balance Test Example (Typical)

The numbers below refer to the step numbers on the diagnostic table.

1. 5: If the pressure drop value for each fuel injector is within 10 kPa (1.5 psi) of the average pressure drop value, the fuel injectors are flowing properly. Calculate the pressure drop value for each fuel injector by subtracting the second pressure reading from the first pressure reading.

Fuel Injector Balance Test with Tech 2

The fuel tank leak test is used to locate any fuel or fuel vapor escaping the fuel tank area. Fuel vapors escaping above the fuel level will be detected when the evaporative emission (EVAP) diagnostics complete one test cycle. The malfunction indicator lamp (MIL) will illuminate after the EVAP diagnostics have failed two test cycles.

1. Operate the vehicle under the condition of the customers concern. Under high temperature conditions fuel vapors may increase to the point of EVAP canister vapor saturation. Fuel vapors would then be released into the atmosphere. Once the engine is running and EVAP purge is enabled, all fuel vapor release would be eliminated.
2. Movement of the EVAP pipes or fuel pipes may help find an intermittent condition.
3. if the fuel level is low, a fuel leak may not be evident.

The numbers below refer to the step numbers on the diagnostic table.

1. 4: This step tests for fuel leaks below the fuel tank fuel level.
2. 5: This step tests for fuel vapors escaping above the fuel level in the fuel tank.

Fuel Tank Leak Test

Water contamination in the fuel system may cause driveability conditions such as hesitation, stalling, no start, or misfires in one or more cylinders. Water may collect near a single fuel injector at the lowest point in the fuel injection system, and cause a misfire in that cylinder. If the fuel system is contaminated with water, inspect the fuel system components for rust, or deterioration.

Alcohol concentrations of 10 percent or greater in fuel can be detrimental to fuel system components. Alcohol contamination may cause fuel system corrosion, deterioration of rubber components, and subsequent fuel filter restriction. Some types of alcohol are more detrimental to fuel system components than others. Ethanol is commonly used in gasoline, but in concentrations of no more than 10 percent. Some fuels, such as E85, contain a very high percentage of ethanol. Fuel with more than 10 percent ethanol may cause driveability conditions such as hesitation, lack or power, stalling, or no start.

Alcohol in Fuel Testing Procedure

The fuel sample should be drawn from the bottom of the tank so that any water present in the tank will be detected. The sample should be bright and clear. If alcohol contamination is suspected then use the following procedure to test the fuel quality.

1. Using a 100 ml specified cylinder with 1 ml graduation marks, fill the cylinder with fuel to the 90 ml mark.
2. Add 10 ml of water in order to bring the total fluid volume to 100 ml and install a stopper.
3. Shake the cylinder vigorously for 10-15 seconds.
4. Carefully loosen the stopper in order to release the pressure.
5. Re-install the stopper and shake the cylinder vigorously again for 10-15 seconds.
6. Put the cylinder on a level surface for approximately 5 minutes in order to allow adequate liquid separation.

If alcohol is present in the fuel, the volume of the lower layer, which would now contain both alcohol and water, will be more than 10 ml. For example, if the volume of the lower layer is increased to 15 ml, this indicates at least 5 percent alcohol in the fuel. The actual amount of alcohol may be somewhat more because this procedure does not extract all of the alcohol from the fuel.

Particulate Contaminants in Fuel Testing Procedure

The fuel sample should be drawn from the bottom of the tank so that any water present in the tank will be detected. The sample should be bright and clear. If the sample appears cloudy, or contaminated with water, as indicated by a water layer at the bottom of the sample, use the following procedure to diagnose the fuel.

1. Using an approved fuel container, draw approximately 0.5 liter of fuel.
2. Place the cylinder on a level surface for approximately 5 minutes in order to allow settling of the particulate contamination.

Particulate contamination will show up in various shapes and colors. Sand will typically be identified by a white or light brown crystals. Rubber will appear as black and irregular particles. If particles are found clean the entire fuel system thoroughly. Refer to Fuel System Cleaning .

Water contamination in the fuel system may cause driveability conditions such as hesitation, stalling, no start, or misfires in one or more cylinders. Water may collect near a single fuel injector at the lowest point in the fuel injection system, and cause a misfire in that cylinder. If the fuel system is contaminated with water, inspect the fuel system components for rust or deterioration.

Ethanol concentrations of greater than 10 percent in non-blended gasoline, or greater than 85 percent with E85 blended gasoline for flexible fuel applications, can cause driveability conditions and may contribute to fuel system deterioration. Excessive ethanol concentrations can result in driveability conditions such as hesitation, lack of power, stalling, or a no start, and may contribute to fuel system corrosion, deterioration of fuel system components, and a restricted fuel filter.

Test Procedure

1. Test the fuel composition using J 44175 Fuel Composition Tester and J 44175-3 Instruction Manual.
2. If water appears in the fuel sample, perform the following steps: Clean the fuel system. Refer to «Fuel System Cleaning»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-introduction) . Replace the fuel filter if the vehicle is equipped with a serviceable fuel filter.
3. Subtract 50 from the reading on the DMM in order to obtain the percentage of alcohol in the fuel sample. Refer to the examples in the Fuel Composition Test Examples table.
4. If the non-blended gasoline fuel sample contains more than 15 percent ethanol, or if the E85 blended gasoline fuel sample contains more than 85 percent ethanol, add fresh, regular gasoline to the vehicle's fuel tank.
5. Test the fuel composition.
6. If additional testing indicates that the ethanol percentage is still more above 15 percent for a non-blended gasoline sample, drain and replace the vehicle's fuel. Refer to «Fuel System Cleaning»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-introduction) . If additional testing indicates that the E85 blended gasoline sample is still above 85 percent, continue adding fresh, regular gasoline until the ethanol content is 85 percent or less.

Fuel Composition Test Examples

The engine idle speed is controlled by the idle air control (IAC) valve. The IAC valve is on the throttle body. The IAC valve pintle moves in and out of an idle air passage bore to control air flow around the throttle plate. The IAC valve consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called steps. The stepper motor has 2 separate windings that are called coils. Each coil is supplied current by 2 circuits from the powertrain control module (PCM). When the PCM changes polarity of a coil, the stepper motor moves one step. The PCM uses a predetermined number of counts to determine the IAC pintle position. Observe IAC counts with a scan tool. The IAC counts will increment up or down as the PCM attempts to change the IAC valve pintle position. An IAC Reset will occur when the ignition key is turned OFF. First, the PCM will seat the IAC pintle in the idle air passage bore. Second, the PCM will retract the pintle a predetermined number of counts to allow for efficient engine start-up. If the engine idle speed is out of range for a calibrated period of time, an idle speed diagnostic trouble code (DTC) sets.

Inspect for the following conditions

1. High resistance in an IAC valve control circuit.
2. The correct positive crankcase ventilation (PCV) valve, properly installed and proper operation of the PCV valve.
3. Proper operation and installation of all air intake components.
4. Proper installation and operation of the mass air flow (MAF) sensor, if equipped.
5. A tampered with or damaged throttle stop screw.
6. A tampered with or damaged throttle plate, throttle shaft, throttle linkage, or cruise control linkage, if equipped.
7. A skewed high throttle position (TP) sensor.
8. Excessive deposits in the IAC passage or on the IAC pintle.
9. Excessive deposits in the throttle bore or on the throttle plate.
10. Vacuum leaks.
11. A high or unstable idle condition could be caused by a non-IAC system problem that can not be overcome by the IAC valve. Refer to «Symptoms - Engine Controls»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting) .
12. If the problem is determined to be intermittent, refer to «Intermittent Conditions»(/chevrolet/chevy-express-g2500/1996-2012/remont/testing-diagnostics/#engine-control-system-48l-53l-60l-troubleshooting__intermittent-conditions) .

The numbers below refer to the step numbers on the diagnostic table.

1. 5: This test will determine the ability of the PCM and IAC valve control circuits to control the IAC valve.
2. 7: This test will determine the ability of the PCM to provide the IAC control valve circuits with a ground. On a normally operating system, the test lamp should not flash while the IAC Counts are incrementing.

Idle Air Control (IAC) System Diagnosis

The electronic ignition system uses an individual ignition coil for each cylinder. The powertrain control module (PCM) controls the ignition operation through 8 individual ignition control (IC) circuits. Each bank of four ignition coils is connected to the PCM, power, and ground by the following circuits

1. The low reference
2. The ground
3. The Ignition 1 voltage
4. The appropriate IC circuit

The PCM triggers an ignition coil by grounding the appropriate IC control using information from the crankshaft position (CKP) and camshaft position (CMP) sensors.

For an intermittent condition, refer to Intermittent Conditions .

The number below refers to the step number on the diagnostic table.

1. 4: Monitoring the misfire current counters determines if a fault is present.

Electronic Ignition (EI) System Diagnosis

Several states require that a vehicle pass on-board diagnostic (OBD) system tests and the inspection/maintenance (I/M) emission inspection in order to renew license plates. This is accomplished by viewing the I/M System Status display on a scan tool. Using a scan tool, the technician can observe the I/M System Status in order to verify that the vehicle meets the criteria that comply with the local area requirements.

Conditions for Updating the I/M System Status

Each system monitor requires at least one, and sometimes several diagnostic tests. The result of each test is reported by a diagnostic trouble code (DTC). A system monitor is complete when either all of the DTCs comprising the monitor have Run and Passed, or when any one of the DTCs comprising the monitor has illuminated the malfunction indicator lamp (MIL). Once the system monitor is complete, the I/M System Status display will indicate YES in the Completed column.

For example, when the HO2S Heater Status indicates YES, either all of the oxygen sensor heater tests have passed or one of the tests has illuminated the MIL. If the vehicle has four heated oxygen sensors, either all four heater circuit tests have passed or one of the heater circuit tests has illuminated the MIL. The I/M System Status will indicate NO under the Completed column when any of the required tests for that system have not run. The following is a list of conditions that would set the I/M System Status indicator to NO

1. The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to complete the tests.
2. The battery has been disconnected or discharged below operating voltage.
3. The control module power or ground has been interrupted.
4. The control module has been reprogrammed.
5. The control module DTCs have been cleared.

Monitored Emission Control Systems

The OBD II System monitors all emission control systems that are on-board. Not all vehicles have a full complement of emission control systems. For example, a vehicle may not be equipped with secondary air injection (AIR) or exhaust gas recirculation (EGR). The OBD II regulations require monitoring of the following

1. The air conditioning system
2. The catalytic converter efficiency
3. Comprehensive component monitoring-Emission related inputs and outputs
4. The evaporative emissions (EVAP) system
5. The EGR System
6. The fuel delivery system
7. Heated catalyst monitoring
8. Misfire monitoring
9. The oxygen sensor system (O2S or HO2S)
10. The oxygen sensor heater system (HO2S heater)
11. The AIR system

For the specific DTCs required for each system, refer to Inspection/Maintenance (I/M) System DTC Table . Systems such as fuel delivery, misfire, and comprehensive components may not be listed in a system status list. These tests run continuously and do not require an I/M System Status indicator.

Inspection/Maintenance (I/M) System Check

The purpose of the inspection maintenance (I/M) Complete System Set Procedure is to satisfy the enable criteria necessary to execute all of the I/M readiness diagnostics, and to complete the trips for those particular diagnostics. When all diagnostic tests are completed, the I/M System Status indicators are set to YES. Perform this test when more than one or all of the I/M System Status indicators are set to NO.

Conditions for Running

Cold Start

1. The barometric pressure (BARO) is more than 75 kPa.
2. The engine coolant temperature (ECT) is between 4-30°C (39-86°F).
3. The intake air temperature (IAT) is between 4-30°C (39-86°F).
4. The difference between the IAT and the ECT is 8°C (14°F) or less.
5. The battery voltage is between 10-18 volts.
6. The fuel level is between 15-85 percent.

Rough road conditions may prevent some of the tests from running. Extreme high or low ambient temperatures may prevent tests such as for the heated oxygen sensor (HO2S) heater and the evaporative emission (EVAP) system from initiating. If a step is interrupted before completion, perform the remaining portion of the set procedures. Any portion of the set procedure that requires the engine at operating temperature may be repeated. This allows most of the diagnostics to run and the remaining tests can be performed using the individual System Set Procedures.

The scan tool can be used in order to monitor each of the I/M System Status indicators during the I/M Complete System Set Procedure. When all of the indicators for a test step have updated to YES, testing can move on to the next step even if the remaining portion of the test is not complete. For example, step 3 is designed to run the EVAP, AIR, and HO2S tests. The procedure instructs the technician to operate the vehicle in the enable conditions for 6 minutes. If all 3 tests have updated to YES within 4 minutes, you do not need to continue with the enable conditions and testing can advance to the next step.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step is to run the HO2S heater tests and initiate the EVAP System Test. Preprogramming the scan tool will reduce the amount of time the oxygen sensor heaters operate while verifying the enable criteria.
2. 3: This step is to run the EVAP, the AIR and the oxygen sensor tests. The EVAP test begins once the engine coolant reaches a calibrated temperature. The AIR test, if equipped, begins shortly after Closed Loop and the indicated speed is achieved. The oxygen sensor tests begin once the engine is at operating temperature, in Closed Loop Fuel Control, and a calibrated amount of time has elapsed.
3. 4: This step is to run the Catalyst Tests. This test runs during the idle period immediately following a cruise period that meets a minimum calibrated RPM and time period.

Inspection/Maintenance (I/M) Complete System Set Procedure

Inspection/Maintenance (I/M) System DTC Table

Inspection/Maintenance (I/M) System DTC Table

The purpose of this test is to satisfy the enable criteria necessary to execute inspection/maintenance (I/M) readiness diagnostics for the catalyst system. The test may be used to set the I/M System Status indicators to YES. The I/M System Status display on the scan tool provides an indication of whether the control module has completed the required tests. The I/M System Status does not indicate that the tests have passed or failed. When all of the diagnostics for a specific system have run and passed, the I/M System Status will update to YES. If a test for a specific system has failed, the I/M System Status will update to YES, indicating a determination was made even if all of the other tests for that system have not run.

1. The engine load must be stable.
2. DTCs P0420 and P0430 are not set.
3. The barometric pressure is more than 74 kPa.
4. The engine coolant temperature (ECT) is between 70-120°C (158-248°F).
5. The engine has been running for more than 10 minutes.
6. The engine is in Closed Loop fuel control.
7. The battery voltage is more than 10-18 volts.
8. The intake air temperature (IAT) is between -7 and +85°C (+20 and +185°F).
9. The difference between the engine speed and the desired engine speed is less than 200 RPM.

The control module runs a calibrated number of catalyst tests per trip until the Catalyst System Status updates to YES. If the status does not update, the test outlined in this procedure can be repeated until the I/M System Status updates to YES.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load such as a cooling fan or A/C compressor clutch turning ON may cause the test to abort.

Inspection/Maintenance (I/M) Catalyst System Set Procedure (Without HP2)

The purpose of this test is to satisfy the enable criteria necessary in order to execute the inspection/maintenance (I/M) readiness diagnostics for the evaporative emission (EVAP) system. The test may be used in order to set the I/M System Status indicators to YES. The I/M System Status Display on the scan tool provides an indication of when the control module has completed the required tests. The I/M System Status does not indicate that the tests have passed or failed. When all of the diagnostics for a specific system have run and passed and I/M System Status will update to YES. If a test for a specific system has failed, the I/M System Status will update to YES, indicating a determination was made, even if all of the other tests for that system have not run. Performing a visual inspection prior to running the EVAP test may prevent having to repeat the test. A failed or aborted test will require the vehicle to cool down in order to meet the enable criteria to run another test.

1. DTCs P0442, P0446, P0455, P0496 are not set.
2. The barometric pressure (BARO) is more than 75 kPa.
3. The fuel level is between 1/4 and 3/4.
4. The battery voltage is between 10-18 volts.
5. The engine coolant temperature (ECT) is between 3.75-30°C (39-86°F).
6. The intake air temperature (IAT) is between 3.75-30°C (39-86°F).
7. The difference between the ECT and the IAT is less than 8°C (14°F).

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load such as cooling fan or an A/C compressor clutch turning ON may cause the test to abort.

Inspection/Maintenance (I/M) Evaporative Emission (EVAP) System Set Procedure

The purpose of this test is to satisfy the enable criteria necessary to execute inspection/maintenance (I/M) readiness diagnostics for the oxygen sensor (O2S, HO2S) system. The test may be used to set the I/M System Status to YES. The I/M System Status display on the scan tool provides an indication of whether the control module has completed the required tests. The I/M System Status does not indicate that the tests have passed or failed. When all of the diagnostics for a specific system have run and passed, the I/M System Status will update to YES. If a test for a specific system has failed, the I/M System Status will update to YES, indicating a determination was made, even if all of the other tests for that system have not run.

1. DTCs P0133, P0135, P0136, P0140, P0141, P0153, P0155, P0156, P0160, P0161, P1133, P1134, P1153, P1154 are not set.
2. The fuel level is more than 10 percent.
3. The engine coolant temperature (ECT) is more than 60°C (140°F).
4. The engine is running in Closed Loop fuel control.
5. The engine has been running for more than 3 minutes.
6. The battery voltage is between 10-18 volts.
7. The mass air flow (MAF) is between 20-55 grams per second.
8. The engine speed is between 1,200-3,000 RPM.
9. The throttle position (TP) sensor is more than 5 percent.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load such as a cooling fan or A/C compressor clutch turning ON may cause the test to abort.

Inspection/Maintenance (I/M) Heated Oxygen Sensor/Oxygen Sensor (HO2S/O2S) System Set Procedure

The purpose of this test is to satisfy the enable criteria necessary to execute inspection/maintenance (I/M) readiness diagnostics for the heated oxygen sensor (HO2S) heater system. The test may be used to set the I/M System Status to YES. The I/M System Status display on the scan tool provides an indication of whether the control module has completed the required tests. The I/M System Status does not indicate that the tests have passed or failed. When all of the diagnostics for a specific system have run and passed, the I/M System Status will update to YES. If a test for a specific system has failed, the I/M System Status will update to YES, indicating a determination was made, even if all of the other tests for that system have not run.

1. DTCs P0135, P0141, P0155, P0161 are not set.
2. The engine has been running for more than 2 minutes.
3. The engine coolant temperature (ECT) is more than 50°C (122°F).
4. The engine speed is between 500-3,000 RPM.
5. The battery voltage is between 10-18 volts.
6. The mass air flow (MAF) is between 3-40 grams per second.

The HO2S Heater Tests will normally run within the 2 minutes allotted in the procedure. If there is an indeterminate condition, the test may take up to 8 minutes on some vehicles before a decision of pass or fail is made. If the test does not update to YES, it may have failed or aborted due to the loss of enabling conditions. Extremely high ambient temperatures may prevent the HO2S Heater Test from initiating.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the service information for an indication of why the test does not complete. Some tests may abort due to changes in the conditions while the test is running. For example, changes in engine load such as a cooling fan or A/C compressor clutch turning ON may cause the test to abort.

Inspection/Maintenance (I/M) Heated Oxygen Sensor (HO2S) Heater System Set Procedure

See also:
• Diagnostic System Check - Engine Controls
• Scan Tool Data List
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Engine Controls Schematics
• Circuit Testing
• Wiring Repairs
• Power Distribution Schematics
• Ground Distribution Schematics
• Checking Aftermarket Accessories
• Diagnostic System Check - Engine Electrical
• Service Programming System (SPS)
• Power and Grounding Component Views
• Temperature vs Resistance
• Spark Plug Inspection
• Spark Plug Wire Inspection
• Oil Consumption Diagnosis
• Engine Compression Test
• Cylinder Head Cleaning and Inspection
• Camshaft and Bearings Cleaning and Inspection
• Piston, Connecting Rod, and Bearings Cleaning and Inspection
• Crankshaft and Bearings Cleaning and Inspection
• Heated Oxygen and Oxygen Sensor Notice
• Exhaust Leakage
• DTC P0300
• Engine Overheating
• Diagnostic Starting Point - Automatic Transmission
• Restricted Exhaust
• Loss of Coolant
• Fan Clutch Diagnosis
• Symptoms - Engine Mechanical
• Diagnostic System Check - Automatic Transmission
• Thermostat Diagnosis
• Crankcase Ventilation System Inspection/Diagnosis
• Symptoms - Instrument Panel, Gages and Console
• Park/Neutral Position Switch Adjustment
• Brakes Drag
• Engine Controls Connector End Views
• Powertrain Control Module (PCM) Connector End Views
• Diagnostic System Check - Instrument Cluster
• Powertrain Control Module (PCM) Replacement
• Diagnostic Trouble Code (DTC) List
• Engine Cranks Slowly
• Diagnostic System Check - Theft Deterrent
• Fuel System Diagnosis
• DTC P0125
• Probing Electrical Connectors
• Fuel Sender Assembly Replacement
• Fuel Pressure Relief Procedure
• Testing for Continuity
• Fuel Injector Cleaning Procedure
• Fuel Injector Balance Test Notice
• Lifting and Jacking the Vehicle
• DTC P0455
• Road Test Caution
• Intermittent Conditions
• Hard Start
• Surges/Chuggles
• Lack of Power, Sluggishness, or Sponginess
• Detonation/Spark Knock
• Hesitation, Sag, Stumble
• Cuts Out, Misses
• Poor Fuel Economy
• Poor Fuel Fill Quality
• Rough, Unstable, or Incorrect Idle and Stalling
• Dieseling, Run-On
• Backfire
• Symptoms - Engine Controls
• Inspection/Maintenance (I/M) System DTC Table