Engine Controls Self-Diagnostics - 2.2L: Overview

MODEL IDENTIFICATION

Vehicle and engine model is identified by Vehicle Identification Number (VIN). VIN is stamped on metal pad on top of left end of instrument panel, near windshield. See MODEL IDENTIFICATION table.

Body Code (1)	Model
J	(2) Cavalier & Sunfire
N	Alero & Grand Am
(1) Vehicle body code is 4th character of VIN. (2) Cavalier is also available with 2.2L Bi-Fuel - CNG/Gasoline engine.

(1)	Vehicle body code is 4th character of VIN.

(2)	Cavalier is also available with 2.2L Bi-Fuel - CNG/Gasoline engine.

MODEL IDENTIFICATION

Description

The Diagnostic System Check - Engine Controls is an organized approach to identifying a condition that is created by a malfunction in the engine control system. The Diagnostic System Check must be the starting point for any driveability concern. The Diagnostic System Check directs the service technician to the next logical step in order to diagnose the concern. Understanding and correctly using the diagnostic table reduces diagnostic time and prevents the replacement of good parts.

Test Description

The numbers below refer to the step numbers on the diagnostic test procedure.

2 - Lack of communication may be a result of a partial or a total malfunction of the class 2 serial data circuit. The specified procedure determines the particular condition.
5 - This step stores the PCM DTC information into the scan tool's memory. After you complete the diagnostic procedure, review the captured information in order to catch the next DTC if the PCM stores multiple DTCs. Review the Freeze Frame/Failure Records data. Use this information in order to determine how frequently and how recently the DTC set. This information may help diagnose an intermittent condition. Information about the operating conditions at the time that the DTC set may also help diagnose an intermittent condition. Capturing the stored information saves the data that the PCM loses during the following conditions: When a diagnostic procedure instructs you to clear DTCs. When a diagnostic procedure instructs you to disconnect the PCM harness connectors. When a diagnostic procedure instructs you to replace PCM.
6 - The presence of DTCs which begin with "U", indicate that some other module is not communicating. Following the specified procedure will gather all the available information before you perform the tests.
8 - If there are other modules with DTCs set, refer to the DTC list. The DTC list directs you to the appropriate diagnostic procedure. If the PCM stores multiple powertrain DTCs, diagnose the DTCs in the following order: Component level DTCs, such as sensor DTCs, solenoid DTCs, and relay DTCs. Diagnose the multiple DTCs within this category in numerical order. Begin with the lowest numbered DTC, unless the diagnostic table directs you otherwise. System level DTCs, for example, misfire DTCs, fuel trim DTCs, and catalyst DTCs.
10 - This step is for areas that have inspection and maintenance testing procedures for emissions testing. Use this step if the testing facility found one or more I/M system statuses that did not set.

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

1 - Any DTCs set, even those that are not listed in the Inspection/Maintenance System DTCs, 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 - Anytime a PCM 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 - 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.

The purpose of the I/M Complete System Set Procedure is to satisfy the enable criteria necessary to execute all of the I/M readiness diagnostics, and 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.

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

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 - This step runs 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. The PCM considers the engine to be cold if the following conditions are met: ECT sensor parameter is less than 84°F (29°C). ECT and IAT are within 13°F (7°C) of each other at start up.
3 - This step runs the EVAP, 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.
4 - This step is to run the EGR tests. The EGR Tests are run during a gradual deceleration with a closed throttle. The vehicle speed is required in order to maintain a high, steady Manifold Absolute Pressure (MAP) signal.
5 - This step runs the catalyst tests. This test runs during the idle period immediately following a cruise period that meets a minimum calibrated RPM and time period.
6 - Perform the individual system test for any of the systems that do not update to YES.
7 - The I/M system status only reports on whether or not a diagnostic has run, not the outcome of the test. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

The following DTCs are required to set system status to YES

Catalyst System

P0420 - TWC System - Low Efficiency (Bank 1)

EVAP System

P0440 - EVAP System
P0442 - EVAP Control System - Small Leak Detected
P0446 - EVAP Vent System Performance
P1441 - EVAP System Flow During Non-Purge

Oxygen Sensor

P0133 - HO2S Slow Response - Sensor 1
P0140 - HO2S 2 Circuit - Insufficient Activity
P1133 - HO2S Insufficient Switching - Sensor 1

Oxygen Sensor Heater

P0135 - HO2S Heater Circuit - Sensor 1
P0141 - HO2S 2 Heater Circuit

Diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .

This test satisfies 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 that 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.

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

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 - The catalyst test during the idle period immediately following the cruise period.
3 - This step identifies a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC 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»(ref-153397-S38513399282003040400000) .
4 - This step identifies 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 Test.
5 - The I/M System Status only verifies whether a diagnostic has run, not the outcome of the test. If any Emission Related DTC sets after the tests are complete, the DTC will require diagnosis.

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. Service Bay Tests are included on the scan tool for some systems depending upon vehicle make and model. The test is designed to allow the EVAP Diagnostic Tests to run in service bay conditions. Ensure the vehicle meets the requirements listed in Conditions for Running before performing either EVAP System Test. Failure to meet the necessary requirements may produce inaccurate test results.

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

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 - This step determines whether or not the EVAP System Test has passed. If the system is operating correctly, the scan tool indicates that the system has passed and the I/M System Status updates to YES. If the EVAP Service Bay Test aborts because of lost enable conditions, the test can be repeated once the enable criteria is met.
4 - A failed DTC during the EVAP Service Bay Test may not appear in the DTC Information display on some vehicles. The Service Bay Test displays an indication of which test failed as a directive to the appropriate service information. Some vehicles will display the test as aborted and the first failure of type "B" DTC appears in the DTC Information.
5 - The EVAP System Test usually begins around an ECT of 176°F (80°C). The vehicle should be operated moderately until this temperature is reached. The engine coolant temperature can be monitored using a scan tool.
6 - This step identifies a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC 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»(ref-153397-S07678929692003040400000) .
7 - This step helps identify any unique or any 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 Test. See «CONDITIONS FOR RUNNING TEST»(ref-153397-S33062742342003040400000) .
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.

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the Oxygen Sensor/Heated 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.

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

1 - Ensure 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 - The oxygen sensor tests begin during the idle period immediately following the cruise period.
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 the DTC 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. See «DIAGNOSTIC AIDS»(ref-153397-S00585315692003040400000) .
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 Test.
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.

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.

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

1 - Ensure 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 - Preprogramming the scan tool will reduce the amount of time the oxygen sensor heaters operate while verifying the enable criteria.
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 the DTC 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»(ref-153397-S42528588242003040400000) .
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 Test.
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.

CONNECTOR IDENTIFICATION

Note. For CNG related connector identification, see SELF-DIAGNOSTICS - 2.2L CAVALIER - BI-FUEL - CNG/GASOLINE article.

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Scheme 1: CONNECTOR IDENTIFICATION

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MIL Operation

MIL is located on instrument panel and is displayed as CHECK ENGINE light.

MIL Function

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

MIL Illumination

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

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

2 - 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.

MIL is located on the instrument panel and is displayed as CHECK ENGINE light.

MIL Function

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

MIL Illumination

The MIL will illuminate with ignition switch in RUN position and the engine not running.
The MIL will turn OFF when the engine is started.
The MIL will remain ON if the self-diagnostic system has detected a malfunction.
The MIL may turn OFF if the malfunction is not present.
If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated so long as the ignition switch is in RUN position.
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 number below refers to the step number on the diagnostic procedures.

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

The Powertrain Control Module (PCM) supplies a 5-volt reference circuit and a low reference circuit to both the Throttle Position (TP) sensor and the Manifold Absolute Pressure (MAP) sensor. The TP sensor sends a voltage signal back to the PCM relative to the throttle plate opening, and the MAP sensor sends a voltage signal back to the PCM relative to the intake manifold pressure. The PCM can detect if the TP sensor or the MAP sensor are out of range by comparing the two values against the high and low limits and engine speed defined within the engine calibration. If the TP or MAP sensors are not within the expected limits of the engine calibration, DTC P0105 is set.

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

8 - While starting the engine, the MAP sensor should detect any changes in manifold pressure. This test is to determine if the sensor is stuck at a value.
9 - A normal MAP sensor will react as quickly to the throttle changes. A MAP sensor should not appear to be "lazy" or catch up with the throttle movements.

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

5-volt reference circuit.
Low reference circuit.
MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition in RUN position, engine OFF, or at a Wide Open Throttle (WOT). The MAP sensor is also used in order to determine the Barometric Pressure (BARO). This occurs when the ignition switch is turned to RUN position, engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range.

If the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 will set.

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

5-volt reference circuit.
Low reference circuit.
MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition switch in RUN position, engine OFF, or at Wide Open Throttle (WOT). The MAP sensor is also used to determine the Barometric Pressure (BARO). This occurs when the ignition switch is turned to RUN position, engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range.

If the PCM detects a MAP sensor signal voltage that is excessively high, DTC P0108 will set.

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

3 - Operate the vehicle within the same conditions which caused the DTC to fail. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in locating an intermittent condition.

The Intake Air Temperature (IAT) sensor is a variable resistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an excessively low IAT signal voltage, indicating a high temperature, DTC P0112 sets.

The Intake Air Temperature (IAT) sensor is a variable resistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an excessively high IAT signal voltage, indicating a low temperature, DTC P0113 sets.

The number below refer to the step number on the diagnostic procedure.

6 - This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively low ECT signal voltage, which is a high temperature indication, DTC P0117 sets.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The ECT sensor has a signal circuit and a low reference circuit. The Powertrain Control Module (PCM) supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively high ECT signal voltage, which is a low temperature indication, DTC P0118 sets.

The Throttle Position (TP) sensor is used by the Powertrain Control Module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with 3 circuits

A 5-volt reference circuit.
A low reference circuit.
A signal circuit.

The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the Wide Open Throttle (WOT) position provides the PCM with a signal voltage from less than one volt to more than 4 volts through the TP sensor signal circuit. If the PCM detects an very low signal voltage, DTC P0122 will set.

The number below refer to the step number on the diagnostic procedure.

7 - Malfunctioning components that share the TP sensor 5-volt reference circuit could cause a low voltage condition on this circuit.

A 5-volt reference circuit.
A low reference circuit.
A signal circuit.

The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the Wide Open Throttle (WOT) position provides the PCM with a signal voltage from less than 1 volt to greater than 4 volts through the TP sensor signal circuit. If the PCM detects an excessively high signal voltage, this DTC will set.

Engine Coolant Temperature (ECT) sensor monitors temperature of the coolant. This input is used by the Powertrain Control Module (PCM) for engine control and as an enabling criteria for some diagnostics.

The air flow into the engine is accumulated and used to determine if the vehicle has been driven within the conditions that would allow the engine coolant to heat up normally to the Closed Loop temperature. If the coolant temperature does not increase normally or does not reach the Closed Loop temperature, the diagnostics that use engine coolant temperature as enabling criteria may not run when expected.

This DTC will only run once per ignition cycle within enabling conditions.

This DTC will set when there has been excessive time to reach closed loop fuel control.

Engine Coolant Temperature (ECT) sensor monitors temperature of coolant. This input is used by PCM for engine control, and as an enabling criteria for some diagnostics.

Air flow coming into engine is accumulated and used to determine if engine has been driven within conditions that would allow engine coolant to heat up normally to thermostat regulating temperature. If coolant temperature does not increase normally, or does not reach regulating temperature of thermostat, diagnostics that use engine coolant temperature as enabling criteria, may not run when expected.

This DTC will only run once per ignition cycle within the enabling condition. If the PCM detects the calibrated amount of air flow and engine run time have been met, and the ECT has not met the minimum thermostat regulating temperature, DTC P0128 sets.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

If the PCM detects the loop status is open too long, DTC P0130 will set.

The number below refer to the step number on the diagnostic procedure.

2 - An HO2S heater fault may set this DTC.
3 - If the voltage is varying above and below the specified value, the condition is not present.

If the PCM detects an HO2S voltage that stays below a specified value, DTC P0131 will set.

The number below refer to the step number on the diagnostic procedure.

2 - When the system is operating correctly, the HO2S 1 voltage should toggle above and below the bias voltage. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.
4 - The specified value is what is measured on a correctly operating system.

If the PCM detects an HO2S voltage that stays above the specified value, DTC P0132 will set.

The number below refer to the step number on the diagnostic procedure.

2 - When the system is operating correctly, the HO2S 1 voltage should toggle at greater than and less than the bias voltage. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.
4 - The specified value is what is measured on a correctly operating system.

This diagnostic will only run once per ignition cycle. The PCM monitors the rich-to-lean and lean-to-rich transition time. A transition is defined as the HO2S voltage changes from above 600 mV to below 300 mV or from below 300 mV to above 600 mV. If the PCM detects that the transition time is too long, DTC P0133 will set.

The number below refer to the step number on the diagnostic procedure.

2 - When the system is operating correctly, the HO2S 1 voltage should toggle at greater than and less than the specified values. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.
4 - The specified value is what is measured on a correctly operating system.
5 - The specified value is what is measured on a correctly operating system.

If the PCM detects that the HO2S voltage remains within the bias voltage range, DTC P0134 will set.

The number below refer to the step number on the diagnostic procedure.

2 - An HO2S heater fault may set this DTC.
3 - If the voltage is varying above and below the specified value, the condition is not present.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the Powertrain Control Module (PCM). The PCM monitors the current flow through the heater for diagnosis.

If the PCM detects that the HO2S heater current is above or below a specified range, DTC P0135 sets.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

If the PCM detects an HO2S voltage that stays below a specified value, DTC P0137 will set.

The number below refer to the step number on the diagnostic procedure.

2 - When the system is operating correctly, the HO2S 2 voltage should toggle greater than and less than the bias voltage.

If the PCM detects an HO2S voltage that stays above a specified value, DTC P0138 will set.

The number below refer to the step number on the diagnostic procedure.

2 - When the system is operating correctly, the HO2S 2 voltage should toggle at greater than and less than the bias voltage.
5 - This step checks the HO2S 2 high signal circuit for a short to voltage.

In order to control emissions, a Three-Way Catalytic (TWC) converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.

The Powertrain Control Module (PCM) has the capability to monitor this process by using a rear Heated Oxygen Sensor (HO2S) 2. The HO2S 2, located in the exhaust stream past the TWC converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front HO2S 1.

Obstruction of the air reference and degraded HO2S 2 performance could result from any attempt to repair the above conditions.

The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.

The number below refer to the step number on the diagnostic procedure.

2 - When the system is operating correctly, the HO2S 2 voltage should toggle above and below the bias voltage.
5 - This step checks the HO2S 2 high signal circuit for a short to voltage.

If the PCM detects that the HO2S voltage remains within the bias voltage range, DTC P0140 will set.

The numbers below refer to the step number in the diagnostic procedure.

2 - An HO2S heater fault may set this DTC.
3 - If the voltage is varying above and below the specified value, the condition is not present.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the Powertrain Control Module (PCM). The PCM monitors the current flow through the heater for diagnosis.

If the PCM detects that the HO2S heater current is above or below a specified range, DTC P0141 sets.

The Powertrain Control Module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during open and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop the PCM adds oxygen sensor inputs to calculate short and long term fuel trim fuel delivery adjustments. Short Term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long Term FT values change slower in response to trends in Short Term FT adjustments. Fuel Trim Index is the average of Short and Long Term Fuel Trim and Purge Learn Memory based on engine speed and load. If the PCM detects an excessively lean condition, DTC P0171 sets.

The number below refer to the step number on the diagnostic procedure.

7 - If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failures may be at fault.

The Powertrain Control Module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled during Open and Closed Loop. During Open Loop the PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop, the oxygen sensor inputs are added and used by the PCM to calculate Short and Long Term Fuel Trim (FT), fuel delivery adjustments. Short Term FT values change rapidly in response to the Heated Oxygen Sensor (HO2S) voltage signals. Long Term FT values change slower in response to trends in Short Term FT adjustments. The fuel trim index is the average of Short and Long Term FT and purge learn memory based on engine speed and load. Fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the Evaporative Emission (EVAP) canister is causing a rich condition. If the PCM detects an excessively rich condition, DTC P0172 sets.

The number below refer to the step number on the diagnostic procedure.

7 - An EVAP canister that is saturated will cause a rich condition. Fuel in the vacuum line to the fuel pressure regulator indicates a bad regulator. If conditions were not corrected, a worn cam, worn intake or exhaust valves or other engine mechanical failure may be at fault.

The Powertrain Control Module (PCM) enables the appropriate fuel injector pulse for each cylinder. Ignition voltage is supplied to the fuel injectors. The PCM controls each fuel injector by grounding the control circuit via a solid state device called a driver. The PCM monitors the status of each driver. If the PCM detects an incorrect voltage for the commanded state of the driver, a fuel injector control circuit DTC sets.

The Powertrain Control Module (PCM) uses information from the Crankshaft Position (CKP) sensor and the Ignition Control Module (ICM) to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way Catalytic Converter (TWC) to overheat under certain driving conditions. The Malfunction Indicator Light (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.

The number below refer to the step number on the diagnostic procedure.

2 - If the actual CKP variation values are not within the learned values, the misfire counters may increment.

The Powertrain Control Module (PCM) uses information from the Crankshaft Position (CKP) sensor and the Ignition Control Module (ICM) in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way Catalytic Converter (TWC) to overheat under certain driving conditions. The Malfunction Indicator Light (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the PCM detects a misfire rate for a specific cylinder sufficient to cause emission levels to exceed mandated standards, DTC P0301, P0302, P0303 or P0304 will set.

The Knock Sensor (KS) system enables the Powertrain Control Module (PCM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The KS is located on the intake side of the engine block. The KS produces an AC voltage signal that varies depending on the vibration level during engine operation. The PCM adjusts the spark timing based on the amplitude and the frequency of the KS signal. The PCM receives the KS signal through a signal circuit. The KS ground is supplied by the PCM through a low reference circuit. The PCM uses the KS signal to calculate the average voltage and then assigns a voltage range value. The PCM should monitor a normal KS signal within the voltage range. If the PCM malfunctions in a manner that will not allow proper diagnosis of the KS system, this DTC sets.

The Knock Sensor (KS) system enables the Powertrain Control Module (PCM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The KS is located on the intake side of the engine block. The KS produces an AC voltage signal that varies depending on the vibration level during engine operation. The PCM adjusts the spark timing based on the amplitude and frequency of the KS signal. The PCM receives the KS signal through a signal circuit. The KS ground is supplied by the PCM through a low reference circuit. The PCM uses the KS signal to calculate the average voltage and then assigns a voltage range value. The PCM should monitor a normal KS signal within the voltage range. If the PCM detects the KS signal outside of the voltage range, or the KS signal is not present, this DTC sets.

The number below refer to the step number on the diagnostic procedure.

2 - This step ensures that the malfunction is present.
3 - This step tests for a KS that is shorted to ground.
4 - This step tests the KS for proper operation.
5 - This step tests for a short to voltage on the KS signal circuit and the KS low reference circuit.

The Crankshaft Position (CKP) sensor signal indicates the crankshaft speed and position. The CKP sensor produces an AC voltage of different amplitude and frequency, depending on the velocity of the crankshaft. The CKP sensor is connected directly to the Powertrain Control Module (PCM). The circuits between the CKP sensor and the PCM consist of the following circuits: The CKP sensor 1 signal circuit and low reference circuit. If the PCM detects an incorrect number of CKP pulses, DTC P0336 sets.

4 - When a Medium Resolution Resync occurs, an engine stumble should also occur. If the electrical connection of a component or an electrical wire is malfunctioning, an engine stumble or a medium resolution resync may be induced by wiggling the circuit or electrical connector.
5 - Operating malfunctioning non-engine related electronic components may emit Electromagnetic Interference (EMI), which may cause a resync. This step determines if the medium resolution resyncs are being caused by an outside source.
6 - Thoroughly check any suspected circuitry.
8 - An intermittent problem may be caused by a number of conditions.

This ignition system does not use a conventional Camshaft Position (CMP) sensor that detects valve train position. The Ignition Control Module (ICM) detects when No. 1 or No. 3 cylinder has fired on its compression stroke using sensing circuitry integrated within each coil. The sensing circuit detects the polarity and the strength of the secondary voltage output, the higher output is always at the event cylinder. The ICM sends a CMP signal to the Powertrain Control Module (PCM) based on the voltage difference between the event and waste cylinder firing energy. This system is called compression sense ignition. By monitoring the CMP and Crankshaft Position (CKP) signals, the PCM can accurately time the operation of the fuel injectors. If the PCM receives an intermittent CMP signal from the ICM, the CMP Resync Counter on the scan tool will increment. When the PCM cannot use the information from the CMP signal, DTC P0340 will set.

The number below refer to the step number on the diagnostic procedure.

4 - This step determines if the ignition system is working correctly.
5 - This step determines if the interconnect is bad or if a poor connection exists between the ICM and the coil cassette.

This ignition system does not use a conventional Camshaft Position (CMP) sensor that detects valve train position. The Ignition Control Module (ICM) detects when No. 1 or No. 3 cylinder has fired on the compression stroke using sensing circuitry integrated within each coil. The sensing circuit detects the polarity and the strength of the secondary voltage output. The higher output is always at the event cylinder. The ICM sends a camshaft position signal to the Powertrain Control Module (PCM) based on the voltage difference between the event and waste cylinder firing energy. This system is called compression sense ignition. By monitoring the camshaft position and crankshaft position signals the PCM can accurately time the operation of the fuel injectors. If the PCM receives an intermittent CMP signal from the ICM then the CMP Resync Counter on the scan tool will increment. When the PCM cannot use the information from the CMP signal, a DTC will set. If the PCM detects too many CMP Resyncs within a calibrated amount of time, DTC P0341 will set.

The number below refer to the step number on the diagnostic procedure.

3 - This step determines if DTC P0341 is the result of a hard malfunction or an intermittent condition.
4 - The counter should stop incrementing with the CMP circuit disconnected and set DTC P0340. If the counter still increments, this indicates that the PCM is malfunctioning.
5 - A faulty electrical connection in the CMP circuit can cause the CMP Resync Counter to increment. Anytime a faulty electrical connection is present, the CMP Reference Activity counter will stop incrementing.

A Three-Way Catalytic (TWC) converter is used in order to control exhaust emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides Of Nitrogen (NOx). The catalyst within the converter promotes a chemical reaction which oxidizes the HC and the CO that is present in the exhaust gas. This process will convert the HC and the CO into a harmless water vapor and CO, and will reduce the NOx, converting the NOx into nitrogen. The catalytic converter also has the ability to store oxygen. The Powertrain Control Module (PCM) has the capability to monitor this process by using a Heated Oxygen Sensor (HO2S) which is in the exhaust stream past the three-way catalytic converter. The HO2S produces an output signal which indicates the oxygen storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. The PCM monitors the catalyst efficiency by first allowing the catalyst to heat, waiting for a stabilization period while the engine is idling. Then, the PCM adds and removes the fuel while monitoring the reaction of the HO2S. When the catalyst is functioning properly, the HO2S 2 response to the extra fuel is slow compared to the O2S 1. When the HO2S 2 response is close to that of the O2S 1, the oxygen storage capability or efficiency of the catalyst is considered to be bad and the Malfunction Indicator Light (MIL) will illuminate.

The number below refer to the step number on the diagnostic procedure.

2 - If any component DTCs are set, diagnose those DTCs first. A malfunction in a component can cause the converter to appear degraded, or may have caused the malfunction.
3 - This step includes checks for conditions that can cause the TWC converter to appear degraded. Before you proceed with this test, repair any conditions that you find.
5 - If you need to replace the TWC converter, be sure that another condition which could cause damage to the converter is not present. Correct any possible causes of converter damage before replacing the catalytic converter in order to avoid damage to the replacement converter.

The PCM tests the Evaporative Emission (EVAP) system for a large leak. The PCM monitors the Fuel Tank Pressure (FTP) sensor signal to determine the EVAP system vacuum level. When the conditions for running are met, the PCM commands the EVAP canister purge valve OPEN and the EVAP vent valve CLOSED. This allows engine vacuum to enter the EVAP system. At a calibrated time, or vacuum level, the PCM commands the EVAP canister purge valve closed, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum level. If the system is unable to achieve the calibrated vacuum level, or the vacuum level decreases too rapidly, this DTC sets.

The following table illustrates the relationship between the ON and OFF states, and the OPEN or CLOSED states of the EVAP canister purge and vent valves. See EVAP CANISTER PURGE & VENT VALVE RELATIONSHIP table.

Control Module Command	EVAP Canister Purge Valve	EVAP Canister Vent Valve
ON	Open	Closed
OFF	Closed	Open

EVAP CANISTER PURGE & VENT VALVE RELATIONSHIP

The number below refer to the step number on the diagnostic procedure.

3 - This test verifies that the EVAP purge valve is electrically functional.
4 - This test verifies that the EVAP vent valve is electrically functional.
9 - Introducing smoke in 15 second intervals may allow smaller leak areas to be more noticeable. When the system is less pressurized, the smoke will sometimes escape in a more condensed manner.
11 - This test verifies that the FTP sensor is accurate. An FTP sensor that does not correctly respond to vacuum, or pressure may cause this DTC to set.

This DTC tests the Evaporative Emission (EVAP) system for a small leak. The PCM monitors the Fuel Tank Pressure (FTP) sensor signal to determine the vacuum decay rate. At an appropriate time, the PCM turns the EVAP canister purge valve ON and the EVAP vent valve ON. This allows the engine to draw a vacuum on the EVAP system. At a calibrated time, or vacuum level, the PCM turns the EVAP canister purge valve OFF, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum decay. If the PCM detects a leak larger than a calibrated amount, this DTC sets.

The following table illustrates the relationship between the ON and OFF states, and the Open or Closed states of the EVAP canister purge and vent valves. See EVAP CANISTER PURGE VALVE/ VENT VALVE RELATIONSHIP table.

Control Module Command	EVAP Canister Purge Valve	EVAP Canister Vent Valve
ON	Open	Closed
OFF	Closed	Open

EVAP CANISTER PURGE VALVE/ VENT VALVE RELATIONSHIP

The number below refer to the step number on the diagnostic procedure.

3 - Introducing smoke in 15 second intervals may allow smaller leak areas to be more noticeable. When the system is less pressurized, the smoke will sometimes escape in a more condensed manner.
5 - This step verifies that repairs are complete and that no other condition is present.

This DTC tests the Evaporative Emission (EVAP) system for a restricted or blocked EVAP vent path. The PCM commands the EVAP canister purge solenoid Open and the EVAP canister vent solenoid Closed. This allows vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the PCM commands the EVAP canister purge solenoid Closed and the EVAP canister vent solenoid Open. The PCM monitors the Fuel Tank Pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near zero in. H2O in a calibrated time, this DTC sets.

The following table illustrates the relationship between the ON and OFF states, and the Open or Closed states of the EVAP canister purge and vent valves. See EVAP CANISTER PURGE & VENT VALVE RELATIONSHIP table.

Control Module Command	EVAP Canister Purge Solenoid	EVAP Canister Vent Solenoid
ON	Open	Closed
OFF	Closed	Open

EVAP CANISTER PURGE & VENT VALVE RELATIONSHIP

The number below refer to the step number on the diagnostic procedure.

5 - This step inspects the EVAP vent solenoid electrical operation.
6 - This step inspects for a restricted EVAP vent solenoid.
7 - This step tests if the restriction is in the EVAP canister or the vent hose.

The Fuel Tank Pressure (FTP) sensor measures the difference between the air pressure or vacuum in the Evaporative Emission (EVAP) system, and the outside air pressure. The PCM supplies a 5-volt reference and a low reference circuit to the FTP sensor. The FTP sensor signal circuit voltage varies depending on EVAP system pressure or vacuum. If the FTP sensor signal voltage goes below a calibrated value, this DTC sets.

The following table illustrates the relationship between the FTP sensor signal voltage and the EVAP system pressure/vacuum. See FTP SENSOR SIGNAL VOLTAGE AND THE EVAP SYSTEM PRESSURE/VACUUM RELATIONSHIP table.

FTP Sensor Signal Voltage	Fuel Tank Pressure
High, Approximately 1.5 Volts or More	Negative Pressure/Vacuum
Low, Approximately 1.5 Volts or Less	Positive Pressure

FTP SENSOR SIGNAL VOLTAGE AND THE EVAP SYSTEM PRESSURE/VACUUM RELATIONSHIP

The number below refer to the step number on the diagnostic procedure.

2 - This step verifies that the condition is present.
4 - This step tests the 5-volt reference of the FTP sensor.
5 - This step tests if another component is causing the 5-volt reference circuit condition.
6 - If the scan tool displays 5 volts, the FTP sensor signal circuit, the FTP sensor 5-volt reference circuit, and the PCM are okay.

The following table illustrates the relationship between FTP sensor signal voltage and the EVAP system pressure/vacuum. See FTP SENSOR SIGNAL VOLTAGE AND THE EVAP SYSTEM PRESSURE/VACUUM RELATIONSHIP table.

The number below refer to the step number on the diagnostic procedure.

2 - This step determines if the condition is present.
4 - This step tests the signal circuit of the FTP sensor.
5 - This step tests the ground circuit of the FTP sensor.
6 - This step tests the 5-volt reference circuit of the FTP sensor.

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 two 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 using 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.

The number below refer to the step number on the diagnostic procedure.

5 - This test will determine the ability of the engine controller and IAC valve circuits to control the IAC valve.
7 - This test will determine the ability of the PCM to provide the IAC circuits with a ground. On a normal operating system, the test light should not flash while the IAC counts are incrementing.

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 valve consists of a movable pintle, driven by a gear attached to a two phase bi-polar permanent magnet electric motor called a stepper motor. The stepper motor is capable of highly accurate rotation, or of movement, called steps. The stepper motor has two separate windings that are called coils. Each coil is fed by two 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 using 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 DTC may set.

The number below refer to the step number on the diagnostic procedure.

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

This diagnostic applies to internal microprocessor integrity conditions within the Powertrain Control Module (PCM). This diagnostic also addresses if the PCM is not programmed.

The number below refer to the step number on the diagnostic procedure.

2 - A DTC P0602 indicates the PCM is not programmed.

This diagnostic will only run once per ignition cycle. The PCM monitors the number of rich-to-lean and lean-to-rich transitions. If the PCM detects that the number of transitions were less than a specified value, DTC P1133 will set.

The number below refer to the step number on the diagnostic procedure.

2 - When the system is operating correctly, the HO2S 1 voltage should toggle at greater than and less than the specified values. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC to duplicate the malfunction that was detected by the PCM.
4 - The specified value is what is measured on a correctly operating system.
5 - The specified value is what is measured on a correctly operating system.

This diagnostic will only run once per ignition cycle. The PCM monitors the rich-to-lean and lean-to-rich transitions. A transition is defined as the HO2S voltage changes from above 650 mV to below 350 mV or from below 350 mV to above 650 mV. If the PCM detects that the difference between the rich-to-lean average transition time and the lean-to-rich transition time is more than a specified value, DTC P1134 will set.

The number below refer to the step number on the diagnostic procedure.

2 - When the system is operating correctly, the HO2S 1 voltage should toggle above and below the specified values. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.
4 - The specified value is what is measured on a correctly operating system.
5 - The specified value is what is measured on a correctly operating system.

If the PCM detects an HO2S voltage that stays below a specified value, DTC P1137 will set.

The number below refer to the step number on the diagnostic procedure.

2 - When the system is operating correctly, the HO2S 2 voltage should toggle above and below the bias voltage.

If the PCM detects an HO2S voltage that stays above a specified value, DTC P1138 will set.

The number below refer to the step number on the diagnostic procedure.

2 - When the system is operating correctly, the HO2S 2 voltage should toggle at greater than and less than the specified values. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC to duplicate the malfunction that was detected by the PCM.
6 - Disconnecting the HO2S 2 and connecting a jumper wire between the HO2S 2 high signal circuit and the HO2S 2 low signal circuit to ground should cause the scan tool to display HO2S 2 voltage below 100 mV. If the signal voltage is still high, this indicates that the PCM is malfunctioning.

The number below refer to the step number on the diagnostic procedure.

2 - When the system is operating correctly, the HO2S 1 voltage should toggle above and below the bias voltage. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC to duplicate the malfunction that was detected by the PCM.
4 - The specified value is what is measured on a correctly operating system.

The crankshaft position system variation learn feature is used to calculate reference period errors caused by slight tolerance variations in the crankshaft, and the crankshaft position sensors. The calculated error allows the Powertrain Control Module (PCM) to accurately compensate for reference period variations. This enhances the ability of the PCM to detect misfire events over a wider range of engine speed and load.

The PCM stores the crankshaft position system variation values after a learn procedure has been performed. If the PCM detects the CKP system variation values are not stored in the PCM memory, DTC P1336 sets.

DTC tests for undesired intake manifold vacuum flow to the Evaporative Emission (EVAP) system. The PCM seals the EVAP system by commanding the EVAP canister purge valve Closed and the EVAP canister vent valve Closed. The PCM monitors the Fuel Tank Pressure (FTP) sensor to determine if a vacuum is being drawn on the EVAP system. If vacuum in the EVAP system is more than a predetermined value within a predetermined time, this DTC sets.

The number below refer to the step number on the diagnostic procedure.

2 - This step inspects for a leaking EVAP purge solenoid.
4 - Removing the fuel fill cap will equalize the pressure inside the tank with atmospheric pressure. At zero in. of H2O the FTP sensor should be near 1.5 volts. If the sensor is not, there is a concern with the sensor or related wiring.

Engine Controls Self-Diagnostics - 2.2L: Overview Pontiac Sunfire I

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MIL Operation

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