Engine Controls - 1.6l (l91) - Troubleshooting & Diagnosis Chevrolet Aveo I

Important Preliminary Checks Before Starting

Perform the Diagnostic System Check - Engine Controls before using the symptom tables. Verify that all of the following conditions are true

1. The engine control module (ECM) and the malfunction indicator lamp (MIL) are operating correctly.
2. There are no diagnostic trouble codes (DTCs) stored.
3. The scan tool data is within the normal operating range.
4. Verify the customer concern and locate the correct symptom listed below. Inspect items indicated under that symptom.
5. Several of the symptom procedures direct the technician to perform a visual/physical inspection. This important step can lead the technician to the cause of the problem without further checks and can save valuable time.
6. Verify the correct installation and operation of electronic options, such as lights and cellular phones.

1. Use the following tables when diagnosing a symptom concern: «Hard Start»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__hard-start) «Surges/Chuggles»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__surgeschuggles) «Lack of Power, Sluggishness, or Sponginess»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__lack-of-power-sluggishness-or-sponginess) «Detonation/Spark Knock»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__detonationspark-knock) «Hesitation, Sag, Stumble»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__hesitation-sag-stumble) «Cuts Out, Misses»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__cuts-out-misses) «Poor Fuel Economy»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__poor-fuel-economy) «Rough, Unstable, or Incorrect Idle and Stalling»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__rough-unstable-or-incorrect-idle-and) «Dieseling, Run-On»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__dieseling-run-on) «Backfire»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__backfire)
2. If the condition cannot be isolated using the appropriate table, refer to «Intermittent Conditions»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__intermittent-conditions) for further diagnosis.

Intermittent Conditions

Intermittent Conditions

Hard Start

Hard Start

Surges/Chuggles

Surges/Chuggles

Lack of Power, Sluggishness, or Sponginess

Lack of Power, Sluggish or Spongy

Detonation/Spark Knock

Detonation/Spark Knock

Hesitation, Sag, Stumble

Hestitation, 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

Back Fire

Circuit Description

Ignition 1 voltage is supplied directly to the malfunction indicator lamp (MIL). The engine control module (ECM) 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 driver information center (DIC)/clock.

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 ECM.

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

1. 4: This step determines if the condition is with the MIL control circuit or the ECM.
2. 5: This step determines if a voltage is constantly being applied to the control circuit.

Malfunction Indicator Lamp (MIL) Inoperative

Ignition 1 voltage is supplied directly to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.

The MIL is located on the driver information center (DIC)/clock.

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 a diagnostic.

MIL Illumination

1. The MIL will illuminate with the 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 no longer present.
5. If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated as 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.

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

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

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 causes an engine not to start. The Engine Cranks but Does Not Run diagnostic table directs the service technician to the appropriate system diagnosis. In order for the engine to start and run, the correct amount of good quality fuel must be properly delivered to each cylinder. The timing of the valve train operation in relation to piston position is also critical, as is mechanical compression of the air/fuel mixture.

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

1. The battery is completely charged. Refer to «Battery Inspection/Test»(/chevrolet/aveo/i-2003-2008/remont/charging-system/#battery-charging-system-and-starting-system) in Engine Electrical.
2. The engine cranking speed is acceptable. Refer to «Engine Cranks Slowly»(/chevrolet/aveo/i-2003-2008/remont/charging-system/#battery-charging-system-and-starting-system__engine-cranks-slowly) in Engine Electrical.
3. There is adequate fuel in the fuel tank.

Diagnostic Aids

Inspect for any of the following conditions

1. Insufficient fuel can cause a no start condition. Thoroughly inspect the fuel delivery system for sufficient fuel volume to the fuel injectors. Inspect the fuel supply components for partial blockage or restrictions.
2. Fuel injectors with partially blocked and restricted nozzles, or a malfunctioning solenoid, can cause a no start condition. Refer to «Fuel Injector Coil Test»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis) and «Fuel Injector Balance Test with Special Tool»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis) .
3. There may be fuel spray at the fuel injectors and the indicated fuel pressure may be correct, yet there may not be enough fuel to start the engine. If the fuel injectors and the injector circuit are OK, and fuel spray is detected, the fuel injector ON time may be inadequate. If the engine control module (ECM) receives incorrect inputs from the various information sensors, the fuel delivered by the fuel injectors may be inadequate to start the engine. Check all the engine data parameters with a scan tool and compare the values indicated with the expected values or the values from a known good vehicle.
4. Check the crankshaft position (CKP) sensor engine reference signal with a scan tool. Observe the Engine Speed parameter while cranking the engine. The scan tool should indicate a steady 200-300 RPM while cranking. If erratic values, such as sudden spikes in the engine speed are displayed, the engine reference signal is not stable enough for the engine to start and run properly.
5. Inspect the engine for good secure electrical grounds. Refer to «Engine Controls Schematics»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-introduction) .
6. If the engine almost starts and then stalls, check for an open in the ground circuits of the CKP sensor and the camshaft position (CMP) sensor.
7. Water or foreign material in the fuel can cause a no start or engine will not stay running condition. During freezing weather water can freeze inside the fuel system. The engine may start after 30 minutes in a heated repair shop. The malfunction may not recur until parked overnight in freezing temperatures. Extreme weather conditions can cause contaminated fuel to prevent the vehicle from starting.
8. A vehicle that starts and runs after being brought to the repair shop for a no start condition, may have an ignition system that is susceptible to moisture. Spray water on the ignition system components and the wiring in order to check for an engine starting or will not stay running concern.

An intermittent malfunction may be caused by fault in any of the critical information or component electrical circuits. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .

Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.

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

1. 2: The listed DTCs can cause a no start. If a DTC is set, diagnose the DTC before using this diagnostic procedure.
2. 4: This step tests for the correct operation of the crankshaft position (CKP) sensor. If there is a condition with the CKP sensor or circuits, engine speed will not be displayed on the scan tool. Depending on the circuit failure, DTC P0337 may not set.
3. 5: It is important to test for the presence of spark from all of the ignition wires.
4. 6: This step tests for proper operation of the ECM control of the fuel pump circuit.

Engine Cranks but Does Not Run

When the ignition is turned ON, the engine control module (ECM) supplies power to the in-tank fuel pump, by energizing the fuel pump relay. The in-tank fuel pump remains ON as long as the engine is cranking or running and the ECM receives crankshaft reference pulses. If there are no reference pulses, the ECM turns the in-tank fuel pump OFF, 2 seconds after the ignition switch is turned ON or 2 seconds after the engine stops running. The electric fuel pump is incorporated into the modular fuel pump and sender assembly design and is located inside the fuel tank. The fuel pump supplies fuel through a fuel filter, also located in the modular fuel pump and sender assembly, through the fuel feed pipes, to the fuel rail assembly. The fuel pump provides fuel at a pressure above the pressure needed by the fuel injectors. The fuel pressure regulator, located in the modular fuel pump and sender assembly, keeps the fuel available to the fuel injectors at a regulated pressure. When the fuel pressure rises above the pressure regulator calibration, the pressure is relieved, with excess fuel exhausted into the modular fuel pump and sender assembly reservoir.

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

1. 1: The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. 3: This step determines whether the fuel pump can provide fuel within the correct regulated pressure range.
3. 4: This step tests that the fuel system can maintain fuel pressure with the pump Off. A fuel pressure drop of more than 34 kPa (5 psi) within the specified time indicates a leak in the fuel system.
4. 11: This step tests for a restriction in the fuel system.

Fuel System Diagnosis

When you turn ON the ignition switch, the control module energizes the fuel pump relay which powers the fuel pump ON. The pump remains ON as long as the engine is cranking or running and the control module receives ignition reference pulses. If there are no reference pulses, the control module shuts the fuel pump OFF within 2 seconds after the ignition was switched to the ON position or if the engine stops.

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

1. The fuse is faulty.
2. There is an intermittent short in the fuel pump power feed circuit.
3. The fuel pump has an intermittent internal condition.

For an intermittent condition, refer to Intermittent Conditions .

Fuel Pump Electrical Circuit Diagnosis

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

1. 2: Command both the ON and OFF states. Repeat the commands as necessary.
2. 3: This step determines if the condition is located on the coil side or the switch side of the circuit.
3. 4: This step verifies that the ECM is providing voltage to the fuel pump relay.
4. 5: This step tests for an open in the ground circuit to the fuel pump relay.
5. 6: This step determines if a voltage is constantly being applied to the fuel pump relay.
6. 13: This step determines if the condition with the circuit is intermittent. If the fuse does not open, inspect the supply voltage circuit between the fuse and the fuel pump for an intermittent condition.
7. 15: Use the same amperage fuse in the jumper as is used to protect the fuel pump circuit.
8. 17: Inspect the ground connection for the fuel pump. Be certain all ground connections are clean and tight.

Fuel Pump Electrical Circuit Diagnosis

The engine control module (ECM) enables the appropriate fuel injector pulse for each cylinder. Ignition voltage is supplied directly to the fuel injectors. The ECM 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. Monitoring the misfire current counters may help to isolate the fuel injector that is causing the condition.
2. Operating the vehicle over a wide temperature range may help isolate the fuel injector that is causing the condition.
3. Perform the fuel injector coil test within the conditions of the customer's concern. A fuel injector condition may only be apparent at a certain temperature, or under certain conditions.

Fuel Injector Coil Test

The engine control module (ECM) enables the appropriate fuel injector pulse for each cylinder. Ignition voltage is supplied to the fuel injectors. The ECM controls each fuel injector by grounding the control circuit via a solid state device called a driver.

1. Performing the Fuel Injector Coil Test may help isolate an intermittent condition. Refer to «Fuel Injector Coil Test»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis) .
2. For an intermittent condition, refer to «Intermittent Conditions»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__intermittent-conditions) .

Fuel Injector Circuit Diagnosis

System Description

The scan tool is first used to energize the fuel pump relay. 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.

Fuel Injector Balance Test Example (Typical)

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

1. 3: The engine coolant temperature (ECT) must be below the operating temperature in order to avoid irregular fuel pressure readings due to hot soak fuel boiling.

Fuel Injector Balance Test with Special Tool

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 emissions (EVAP) leak diagnostic completes one test cycle.

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.

1. 3: This step tests for location of fuel leakage in the fuel lines.
2. 4: This step tests for fuel leaks below the fuel level in the fuel tank.
3. 5: This step tests for a location of 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 rail, 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 more than 10 percent in the fuel can be detrimental to fuel system components. Alcohol contamination may cause fuel system corrosion, deterioration of rubber components, and subsequent fuel filter restriction. Fuel contaminated with alcohol may cause driveability conditions such as hesitation, lack of power, stalling, or no start. Some types of alcohol are more detrimental to fuel system components than others.

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 (3.38 oz) specified cylinder with 1 ml (0.34 oz) graduation marks, fill the cylinder with fuel to the 90 ml (3.04 oz) mark.
2. Add 10 ml (0.34 oz) of water in order to bring the total fluid volume to 100 ml (3.38 oz) 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, that now contains both alcohol and water, will be more than 10 ml (0.37 oz). For example, if the volume of the lower layer is increased to 15 ml (0.51 oz), 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 contaminants 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 (0.53 qt) 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 can cause driveability conditions and fuel system deterioration. Fuel with more than 10 percent ethanol could result in driveability conditions such as hesitation, lack of power, stalling, or no start. Excessive concentrations of ethanol used in vehicles not designed for it may cause fuel system corrosion, deterioration of rubber components, and fuel filter restriction.

Test Procedure

1. Test the fuel composition using J 44175 Fuel Composition Tester and J44175-3 Instruction Manual.
2. If water appears in the fuel sample, perform the following steps: Clean the fuel system. Refer to «Fuel System Cleaning»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-introduction__fuel-system-cleaning) . Replace the fuel filter. Refer to «Fuel Sender Assembly Replacement»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-introduction) .
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 fuel sample contains more than 15 percent ethanol, add fresh, regular gasoline to the vehicle's fuel tank.
5. Test the fuel composition.
6. If testing shows the ethanol percentage is still more than 15 percent, replace the fuel in the vehicle. Refer to «Fuel Tank Draining Procedure»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-introduction__fuel-tank-draining-procedure) .

Fuel Composition Test Examples

The engine control module (ECM) controls the engine idle speed by adjusting the position of the idle air control (IAC) valve pintle. The IAC valve is a stepper motor driven by two internal coils. The movement of the IAC valve is controlled electrically by four circuits. Drivers within the ECM control the polarity of the two windings inside the IAC valve through these circuits. The ECM, by commanding the correct polarity in sequence, is able to command the motor within the IAC valve to rotate clockwise or counter clockwise in steps. In order for the armature of the stepper motor of the IAC valve to turn one revolution, it needs to move approximately twenty four steps. The IAC valve motor is linked by a gear drive to the IAC valve pintle. The electrical pulses sent to the IAC valve coils, by the ECM, allows the pintle to extend or retract into the passage in the throttle body. By retracting the pintle, air is allowed to bypass the throttle valve, which will increase air flow and raise engine speed. When the pintle is extended, bypass air is decreased which lowers engine speed. IAC valve movement is measured in counts on the scan tool. Each count is equivalent to a step of the IAC valve. When the IAC valve is fully extended, and seated in the throttle body bore, the scan tool displays zero and the engine speed is slow. As the IAC valve pintle retracts the counts will raise along with engine speed.

IAC Valve Reset

When the ignition switch is turned OFF for more than ten seconds an IAC valve reset occurs. At that time, the ECM commands the IAC valve to extend for a certain period which allows the IAC pintle to seat in the throttle body bore. This position is then sensed as zero count position for the IAC valve by the ECM. It must be observed that the IAC valve position is only sensed by the ECM measuring counts or steps of the driver circuit, there is no direct sensing of its exact position. When this extend time period ends, the ECM then commands the IAC valve to retract a predetermined amount. This will allow for a high engine speed on the next ignition cycle. If for any reason the IAC valve pintle moves after this reset, before the next ignition cycle, the ECM will not be able to detect it and will affect the ability to control engine idle. When the IAC valve is removed or replaced for any reason the reset must be performed.

1. A low, high, or unstable idle condition could be caused by a non-IAC system condition that can not be overcome by the IAC valve. Refer to «Symptoms - Engine Controls»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis) .
2. If the condition is intermittent, refer to «Intermittent Conditions»(/chevrolet/aveo/i-2003-2008/remont/testing-diagnostics/#engine-controls-16l-l91-troubleshooting-diagnosis__intermittent-conditions) .

Idle Air Control (IAC) System Diagnosis

An intake manifold tuning (IMT) valve or variable geometry induction system (VGIS) is used to change the intake manifold plenum configuration. When the IMT valve is open, the intake manifold is configured to one large plenum. When the IMT valve is closed, the intake manifold is configured to 2 smaller plenums. The IMT valve improves engine performance at low and high engine speeds depending on the engine load. Ignition 1 voltage is supplied directly to the IMT valve solenoid. The engine control module (ECM) controls the solenoid by grounding the control circuit. The IMT valve system contains the following components

1. The IMT valve solenoid
2. The IMT valve vacuum reservoir
3. The IMTV valve vacuum actuator
4. The intake manifold tuning valve
5. The intake manifold

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

1. 3: This step determines that the IMT valve and linkage is moving correctly and not loose or damaged.

1. 7: This step tests for a faulty IMT valve solenoid. If the IMT valve solenoid is commanded ON, there should be vacuum at the vacuum actuator. If the IMT valve solenoid is commanded OFF, there should be no vacuum at the vacuum actuator.

Intake Manifold Tuning (IMT) Valve Diagnosis

The Electronic Ignition (EI) System uses a waste spark method of spark distribution. The CKP sensor sends reference pulses to the engine control module (ECM). The ECM then triggers the EI system ignition coil. Once the ECM triggers the ignition coil, both of the connected spark plugs ignite at the same time. One cylinder is on its compression stroke at the same time that the other is on the exhaust stroke, resulting in lower energy needed to ignite the spark plug in the cylinder on its exhaust stroke. This leaves the remainder of the high voltage to be used to ignite the spark plug in the cylinder on its compression stroke. The ignition coil consists of the following circuits

1. The ignition 1 voltage
2. The ignition control 1 and 4
3. The ignition control 2 and 3

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

1. 4: This step tests for a short to ground in the ignition 1 voltage circuit.
2. 5: This step test for a fault in the ignition 1 voltage circuit.

1. 6: This step test for high resistance. Three ohms or more can cause can cause a driveability condition.

Electronic Ignition (EI) System Diagnosis

Inspection Procedure

1. Inspect the positive crankcase (PCV) ventilation valve, the PCV hoses, and all connections for leaks or restrictions. Repair as necessary.
2. Start the engine.
3. At idle, listen to the PCV valve while lightly pinching the PCV hose with your fingers or pliers. Perform this test several times. Each time the hose is pinched, the valve should make an audible click.
4. If there is no click, inspect the PCV valve grommet for cracks or damage.
5. Blow air into the PCV valve. The air should pass through the PCV valve with high resistances.
6. If the grommet is OK, replace the PCV valve.

Several states require that a vehicle pass on-board diagnostic (OBD) system tests and the 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 complies with the local area requirements.

Conditions for Updating the I/M System Status

Each system requires at least one, and sometimes several, diagnostic tests. The results of these tests are 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 any one of the DTCs comprising the monitor have illuminated the malfunction indicator lamp (MIL). Once all of the tests are completed, the I/M System Status display will indicate YES in the Completed column. For example, when the heated oxygen sensor (HO2S) Heater Test indicates YES, all of the oxygen sensor heaters have been diagnosed. If the vehicle has four heated oxygen sensors, all four heater circuits have been diagnosed. 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 as part of a service procedure.

Monitored Emission Control Systems

The OBD II system monitors all emission control systems that are on-board. Not all vehicles need every possible emission control system. 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; if equipped

1. Air conditioning system refrigerant
2. Catalytic converter efficiency
3. Comprehensive component monitoring-Emission related inputs and outputs
4. Evaporative emissions (EVAP) system
5. Fuel delivery system
6. Heated catalyst monitoring
7. Misfire monitoring
8. Oxygen sensor system (O2S or HO2S)
9. Oxygen sensor heater system (HO2S Heater)

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 on some vehicles and may not require an indicator.

The I/M System Status display provides an indication of when the control module has completed the required tests. This does not necessarily mean that the test has passed, only that a decision was made. If the diagnostic fails, a DTC will indicate the failure. If a failure indication is present for a DTC associated with one of the I/M regulated systems, it may prevent other required tests from running. For example, a DTC for the control circuit of the EVAP purge solenoid may not be listed in the Inspection/Maintenance System DTC Table because it is a continuous test. If this DTC is set, the Active Tests for the EVAP system may not run.

The I/M System Status information may be useful for a technician to determine if diagnostics have run when verifying repairs.

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

1. 1: Any DTCs set, even those that are not listed in the Inspection/Maintenance System DTC Table, may prevent the required DTCs from running. If there is any question as to whether a set DTC is disabling the required I/M diagnostic, review the Conditions for Running in the diagnostic procedures for the DTC required by the I/M diagnostic. A list of disabling DTCs, if applicable, is contained in the supporting text for that DTC.
2. 2: Anytime a control module is reprogrammed or the diagnostic trouble codes are cleared as part of a repair procedure, all the I/M System Status indicators will reset to NO.
3. 3: Use discretion when determining whether the entire system set procedure needs to be performed. For example, if the only tests that have not run are those that require the engine to be at operating temperature, then only those individual tests need to be run. There is no need to allow the engine to completely cool in order to run these tests.

Inspection/Maintenance (I/M) System Check

The purpose of this procedure is to satisfy the criteria necessary to execute all of the I/M readiness diagnostics. This includes completing 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 if more than one of the I/M System Status indicators is set to NO.

Conditions for Running

1. The barometric pressure (BARO) is more than 72 kPa.
2. The engine coolant temperature (ECT) at start-up is more than -5°C (23°F).
3. The intake air temperature (IAT) at start-up is less than 40°C (104°F).
4. The start-up IAT minus the actual IAT are within 3°C (5°F).
5. The engine is OFF for more than 6 hours or the following conditions must be met: The start-up IAT minus start-up ECT are within 12°C (22°F). The start-up ECT minus start-up IAT are within 50°C (90°F).
6. The ignition 1 voltage is between 10-16 volts.
7. The fuel level is between 1/4 and 3/4.

Rough road conditions may prevent some of the tests from running. Extreme high or low ambient temperatures may prevent tests such as heated oxygen sensor (HO2S) heater and 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.

If the vehicle has recently run, start this procedure at step 3. This will allow the tests that require the engine at operating temperature to run. Using this method allows shorter cool down periods if the tests requiring a cold start do not initiate.

The scan tool can be used 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 HO2S test. The procedure instructs the technician to operate the vehicle in the enable conditions for 8-10 minutes. If the test has updated to YES within 4 minutes, it is not necessary 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. 1: Make sure you perform the I/M system check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2: This step is to initiate the HO2S heater tests.
3. 3: This step is to run the oxygen sensor test. 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.
4. 4: This step is to run the EVAP test. This test runs during the idle period immediately following a cruise period that meets a minimum calibrated RPM and time period.
5. 5: This step is to run the EGR test. This test runs during the deceleration period immediately following a cruise period that meets a minimum calibration vehicle speed.
6. 6: This step is to run the catalyst test. This test runs during idle immediately following a cruise portion that meets the minimum airflow and duration conditions.
7. 7: Perform the individual system test for any of the systems that do not update to YES.
8. 8: The I/M system status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

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 I/M readiness diagnostics for the catalyst system. The test may be used to set the I/M System Status indicators to YES. Ensure the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

1. The engine is operating for more than 10 minutes.
2. The airflow into the engine is more than 12 g/s for 45 seconds. This requires that the vehicle be driven and then allow the engine to idle.
3. The engine coolant temperature is between 70-109°C (158-228°F).
4. The intake air temperature (IAT) is between -7°C and +105°C (19-221°F).
5. The A/C compressor is not cycling.
6. The engine is in closed loop fuel control.

If the status does not update, repeat this test until the I/M System Status updates to YES.

The I/M System Status does not indicate whether the test has passed or failed, only that a decision was made. 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 required tests have not run. When a failure occurs, the Emission Related DTC portion of the I/M System Status display will indicate the malfunction indicator lamp (MIL) is requested. The I/M System Status also registers the number of diagnostic trouble codes (DTCs).

The first failure of a type B DTC does not constitute a final determination of pass or fail, and will not update the I/M System Status to YES. A second trip is required, and all the conditions to run must be met in order for the test to run again. These conditions may include a partial to complete engine cool down.

The I/M System Status will update only when an emission related DTC fails the second time, or when all of the tests pass.

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 an A/C compressor clutch turning ON, may cause the test to abort.

If a diagnostic test is difficult to run, maintain necessary enable conditions until the system status updates to YES.

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

1. 1: Perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2: The Catalyst Test runs during the specified idle period.
3. 3: This step is to identify a first failure of a type B DTC. A DTC only appears on the I/M System Status display when it becomes a MIL illuminating DTC. This occurs on the second failure of a type B DTC. A first failure of a type B DTC will not allow the I/M System Status to update to YES. Refer to Diagnostic Aids.
4. 4: This step is to help identify any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions for Running the DTC.
5. 5: The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

Inspection/Maintenance (I/M) Catalyst 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 exhaust gas recirculation (EGR) 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 barometric pressure is more than 72 kPa.
2. The engine speed is between 1,400-2,900 RPM for manual transmission and 1,550-2,900 RPM for automatic transmission.
3. The vehicle speed is more than 32 km/h (20 mph) during deceleration.
4. The throttle is closed during the deceleration test.

The control module only runs the EGR Active Tests during a gradual deceleration with a closed throttle and a vehicle speed above 32 km/h (20 mph). Several deceleration cycles may be necessary in order to accumulate a sufficient number of EGR flow samples. The procedure outlined in the table is for a clear, flat road. If the procedure is performed on a road with a slight down hill grade, the test may acquire the necessary sample counters in one or two decel trips. If the test is interrupted during the procedure, it may take more than three deceleration cycles to complete the test. 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.

If a diagnostic test is difficult to run, observe the I/M System Status display while maintaining the necessary enable conditions until the System Status updates to YES.

Inspection/Maintenance (I/M) Exhaust Gas Recirculation (EGR) System Set Procedure

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the evaporative emission (EVAP) system. The test may be used to set the I/M System Status indicators to YES. Ensure the vehicle meets the requirements listed in Conditions for Running before performing the EVAP System Test. Failure to meet the necessary requirements may produce inaccurate test results.

1. The barometric pressure (BARO) is more than 72 kPa.
2. The engine coolant temperature (ECT) at start-up is more than -5°C (23°F).
3. The intake air temperature (IAT) at start-up is less than 40°C (104°F).
4. The start-up IAT minus IAT are within 3°C (5°F).
5. The engine is OFF for more than 6 hours or the following conditions must be met: The start-up IAT minus start-up ECT are within 12°C (22°F). The start-up ECT minus start-up IAT are within 50°C (90°F).
6. The fuel level is between 1/4 and 3/4.
7. The ignition 1 voltage is between 10-16 volts.

1. Extreme high or low ambient temperatures may prevent the EVAP system tests from initiating. Performing a visual inspection prior to running the EVAP Test may prevent having to repeat the test. A loose fuel cap may cause the test to abort or fail and prevent the I/M System Status from updating. A failed or aborted test will require the engine to cool down in order to meet the enable criteria to run another test.
2. The I/M System Status does not indicate whether the test has passed or failed, only that a decision was made. 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 required tests have not run. When a failure occurs, the Emission Related DTC portion of the I/M System Status display will indicate the malfunction indicator lamp (MIL) is requested. The I/M System Status also registers the number of diagnostic trouble codes (DTCs).
3. The first failure of a type B DTC does not constitute a final determination of pass or fail, and will not update the I/M System Status to YES. A second and third trip is required, and all the conditions to run must be met in order for the test to run again. These conditions require a complete engine cool down before the EVAP I/M ready status changes to YES.
4. The I/M System Status will update only when an emission related DTC fails the second time, or when all of the tests pass.
5. 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 an A/C compressor clutch turning ON, may cause the test to abort.
6. If a diagnostic test is difficult to run, maintain necessary enable conditions until the system status updates to YES.

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

1. 1: Make sure you perform the I/M system check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 3: This step is to identify a first failure of a type B DTC. A DTC only appears on the I/M System Status display when it becomes a MIL illuminating DTC. This occurs on the second failure of a type B DTC. A first failure of a type B DTC will not allow the I/M System Status to update to YES. Refer to Diagnostic Aids.
3. 4: This step is to help identify any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions for Running the DTC.
4. 5: The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

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

The purpose of this test is to satisfy the enable criteria necessary to execute 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. Ensure the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

1. The engine coolant temperature (ECT) is more than 70°C (158°F).
2. The ignition 1 voltage is more than 10 volts.
3. The engine is operating for more than 60 seconds.
4. The EVAP purge command is less than 20 percent.
5. The engine speed is between 1,500-3,000 RPM.
6. The airflow into the engine is between 9-30 g/s. This requires that the vehicle be driven and then allow the engine to idle.

If the status does not update, repeat this test until the I/M System Status updates to YES.

The I/M System Status does not indicate whether the test has passed or failed, only that a decision was made. 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 required tests have not run. When a failure occurs, the Emission Related DTC portion of the I/M System Status display will indicate the malfunction indicator lamp (MIL) is requested. The I/M System Status also registers the number of diagnostic trouble codes (DTCs).

The first failure of a type B DTC does not constitute a final determination of pass or fail, and will not update the I/M System Status to YES. A second trip is required, and all the conditions to run must be met in order for the test to run again. These conditions may include a partial to complete engine cool down.

The I/M System Status will update only when an emission related DTC fails the second time, or when all of the tests pass.

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 an A/C compressor clutch turning ON, may cause the test to abort.

If a diagnostic test is difficult to run, maintain necessary enable conditions until the system status updates to YES.

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

1. 1: Make sure you perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2: The oxygen sensor tests begin shortly after the indicated speed is achieved. The engine speed may be too low in overdrive on manual transmission vehicles. If difficulty is encountered updating the status, operate the vehicle in the recommended gear during the test.
3. 3: This step is to identify a first failure of a type B DTC. A DTC only appears on the I/M System Status display when it becomes a MIL illuminating DTC. This occurs on the second failure of a type B DTC. A first failure of a type B DTC will not allow the I/M System Status to update to YES. Refer to Diagnostic Aids.
4. 4: This step is to help identify any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions for Running the DTC.
5. 5: The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any Emission Related DTC sets after the tests are complete, the DTC will require diagnosis.

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 I/M readiness diagnostics for the heated oxygen sensor (HO2S) system. The test may be used to set the I/M System Status to YES. Ensure the vehicle meets the requirements listed in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

1. The engine is running.
2. The ignition 1voltage is more than 10 volts.
3. The manifold absolute pressure (MAP) is less than 65 kPa.

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 within the allotted period of time, continue operation within the enable conditions until the test updates to YES. 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. The oxygen sensor heaters are operated by the engine control module. The control module has the ability to monitor the current required by the heaters and does this on a continuous basis.

The I/M System Status does not indicate whether the test has passed or failed, only that a decision was made. 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 required tests have not run. When a failure occurs, the Emission Related DTC portion of the I/M System Status display will indicate the malfunction indicator lamp (MIL) is requested. The I/M System Status also registers the number of diagnostic trouble codes (DTCs).

The first failure of a type B DTC does not constitute a final determination of pass or fail, and will not update the I/M System Status to YES. A second trip is required, and all the conditions to run must be met in order for the test to run again. These conditions may include a partial to complete engine cool down.

The I/M System Status will update only when an emission related DTC fails the second time, or when all of the tests pass.

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 an A/C compressor clutch turning ON, may cause the test to abort.

If a diagnostic test is difficult to run, maintain necessary enable conditions until the system status updates to YES.

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

1. 1: Make sure you perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2: Preprogramming the scan tool will reduce the amount of time the oxygen sensor heaters operate while verifying the enable criteria. The HO2S Heater Tests may not complete when initiated from a cold start and may require running under a load in order to complete the tests.
3. 3: This step is to identify a first failure of a type B DTC. A DTC only appears on the I/M System Status display when it becomes a MIL illuminating DTC. This occurs on the second failure of a type B DTC. A first failure of a type B DTC will not allow the I/M System Status to update to YES. Refer to Diagnostic Aids.
4. 4: This step is to help identify any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions for Running the DTC.
5. 5: The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

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

See also:
• Diagnostic System Check - Engine Controls
• Emission Hose Routing Diagram
• Testing for Electrical Intermittents
• Testing for Continuity
• Charging System Test
• Symptoms - Engine Electrical
• DTC P0506 or P0507
• Ignition System Specifications
• DTC P0172
• Loss of Coolant
• Symptoms - Automatic Transmission
• Symptoms - HVAC Systems - Manual
• DTC P0327
• Symptoms - Engine Exhaust
• Draining and Filling Cooling System
• Engine Overheating
• Symptoms - Engine Cooling
• Thermostat Diagnosis
• Symptoms - Hydraulic Brakes
• Engine Controls Connector End Views
• Clock Malfunction
• Clock Replacement - Console
• Circuit Testing
• Wiring Repairs
• Testing for Intermittent Conditions and Poor Connections
• Connector Repairs
• Battery Inspection/Test
• Engine Cranks Slowly
• Diagnostic Trouble Code (DTC) List
• Diagnostic System Check - Theft Deterrent
• Restricted Exhaust
• Fuel Pressure Relief Procedure
• Probing Electrical Connectors
• Lifting and Jacking the Vehicle
• Special Tools
• Fuel System Cleaning
• Fuel Tank Draining Procedure
• Road Test Caution
• Hard Start
• Surges/Chuggles
• Lack of Power, Sluggishness, or Sponginess
• Detonation/Spark Knock
• Hesitation, Sag, Stumble
• Cuts Out, Misses
• Poor Fuel Economy
• Rough, Unstable, or Incorrect Idle and Stalling
• Dieseling, Run-On
• Backfire
• Intermittent Conditions
• Symptoms - Engine Controls
• Inspection/Maintenance (I/M) System DTC Table