Engine Controls - 2.2l (DTC p0137 to p0449) Chevrolet Cobalt I

Circuit Description

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 engine control module (ECM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the ECM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream, and low HO2S voltage indicates a lean exhaust stream. If the ECM detects an HO2S 2 voltage that stays below a specified value, DTC P0137 will set.

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC P0137 HO2S Circuit Low Voltage Sensor 2

Conditions for Running the DTC

1. DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0171, P0172, P0300, P0336, P0340, P0341, P0455, P0500, P0601, P0602, P0606, P0641, P0722, P0723 are not set.
2. The Loop Status parameter is closed.
3. The Air Fuel Ratio parameter is between 14.5:1 and 14.8:1.
4. The transmission is in Drive with automatic transmission.
5. DTC P0137 runs continuously when the above conditions are met.

Conditions For Setting The DTC

Lean Test

1. The ECM detects that the HO2S 2 voltage parameter is less than 22 mV.
2. DTC P0137 sets during the lean test within 100 seconds when the above condition is met.

OR

Power Enrichment Test

1. The ECM detects that the HO2S 2 voltage parameter is less than 291 mV.
2. DTC P0137 sets during the power enrichment test when the above condition is met.

Action Taken When the DTC Sets

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

Test Description

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

1. 2: If the voltage is less than the specified value, the condition is present.

DTC P0137

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 engine control module (ECM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the ECM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream, and low HO2S voltage indicates a lean exhaust stream. If the ECM detects that HO2S 2 voltage stays above a specified value, DTC P0138 will set.

This diagnostic procedure supports the following DTC

DTC P0138 HO2S Circuit High Voltage Sensor 2

1. DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0171, P0172, P0300, P0336, P0340, P0341, P0455, P0500, P0601, P0602, P0606, P0641, P0722, P0723 are not set.
2. The Loop Status parameter is closed.
3. The Air Fuel Ratio parameter is between 14.5:1 and 14.8:1.
4. The transmission is in Drive with automatic transmission.
5. DTC P0138 runs continuously when the above conditions are met.

Rich Test

1. The ECM detects that the HO2S 2 voltage parameter is more than 1,065 mV.
2. DTC P0138 sets during the rich test within 100 seconds when the above condition is met.

Decel Fuel Cutoff Test

1. The ECM detects that the HO2S 2 voltage parameter is more than 587 mV.
2. DTC P0138 sets during the decel fuel cutoff test within 10 seconds when the above condition is met.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

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

1. 2: If the voltage is more than the specified value, the condition is present.

DTC P0138

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 engine control module (ECM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the ECM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream, and low HO2S voltage indicates a lean exhaust stream. If the ECM detects that HO2S 2 voltage stays between a specified range, DTC P0140 will set.

This diagnostic procedure supports the following DTC

DTC P0140 HO2S Circuit Insufficient Activity Sensor 2

1. DTCs P0037, P0038, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0141, P0171, P0172, P0300, P0336, P0340, P0341, P0455, P0500, P0601, P0602, P0606, P0641, P0722, P0723 are not set.
2. The Engine Run Time parameter is more than 60 seconds.
3. DTC P0140 runs once per drive cycle when the above conditions are met.

1. The ECM detects that the HO2S 2 voltage parameter is between 420-481 mV.
2. DTC P0140 sets within 150 seconds when the above condition is met.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

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

1. 2: If the voltage changes more than the specified value, the condition is not present.

DTC P0140

The heated oxygen sensor (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 engine control module (ECM). The ECM commands the heater ON or OFF to maintain a specific HO2S operating temperature range. The ECM monitors the current flow through the heater for diagnosis. If the ECM detects that the current is above or below a specified range, DTCs P0141 sets.

DTC Descriptors

This diagnostic procedure supports the following DTC

DTC P0141 HO2S Heater Performance Sensor 2

1. The Ignition 1 parameter is more than 10.9 volts.
2. The engine is running.
3. The affected HO2S Heater Command parameter is ON.
4. DTC P0141 runs twice per drive cycle when the above conditions are met.

1. The ECM detects that the affected HO2S Heater Current parameter is more than 1.502 amps or less than 0.249 amps.
2. DTC P0141 sets within 5 seconds when the above condition is met.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0141

The engine control module (ECM) 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 Loop and Closed Loop (CL). During Open Loop, the ECM determines fuel delivery based on sensor signals, without heated oxygen sensor (HO2S) input. During CL, the ECM adds HO2S inputs to calculate the short and long term fuel trim (FT) adjustments. If the HO2S indicates a lean condition, the fuel trim values will be above 0 percent. If the HO2S indicates a rich condition, the FT values will be below 0 percent. The short term FT values change rapidly in response to the HO2S voltage signals. The long term FT makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. A block of cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term FT diagnostic is based on an average of cells currently being used. The ECM selects the cells based on the engine speed and load. If the ECM detects an excessively lean condition, DTC P0171 sets.

This diagnostic procedure supports the following DTC

DTC P0171 Fuel Trim System Lean

1. DTCs P0030, P0036, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0130, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0201-P0204, P0300, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0496, P0506, P0507, P1106, P1107, P1133 are not set.
2. The engine is in CL status.
3. The engine coolant temperature (ECT) is between -40 and +127°C (-40 and +260.6°F).
4. The intake air temperature (IAT) is more than -20°C (-4°F).
5. The manifold absolute pressure (MAP) is more than 5 kPa (0.7 psi).
6. The vehicle speed is less than 134 km/h (83 mph).
7. The engine speed is between 400-6,000 RPM.
8. The mass air flow (MAF) is more than 0.5 g/s.
9. The barometric pressure (BARO) is more than 70 kPa (10.2 psi).
10. The fuel level is more than 10 percent.
11. DTC P0171 runs continuously once the above conditions have been met.

1. The long term FT weighted average value is more than a calibrated value.
2. The above condition is present for more than 2 minutes.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

1. Test for fuel contamination. Small amounts of water can be delivered to the fuel injectors and cause a lean exhaust indication. A lean exhaust indication can also be caused by too much alcohol in the fuel. Refer to «Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool)»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-troubleshooting-diagnosis) or «Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool)»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-troubleshooting-diagnosis) .
2. The system will go lean if an injector is not supplying enough fuel.
3. A lean condition could be present during high fuel demand due to a fuel pump that does not pump enough fuel, a plugged fuel filter, or a restricted fuel pipe.
4. Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to «Intermittent Conditions»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-troubleshooting-diagnosis__intermittent-conditions) .

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

1. 8: If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be at fault.

DTC P0171

The engine control module (ECM) 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 Loop and Closed Loop (CL). During Open Loop, the ECM determines fuel delivery based on sensor signals, without heated oxygen sensor (HO2S) input. During CL, the ECM adds HO2S inputs and level of purge to calculate the short and long term fuel trim (FT) adjustments. If the HO2S indicate a lean condition, the FT values will be above 0 percent. If the HO2S indicate a rich condition, the FT values will be below 0 percent. The short term FT values change rapidly in response to the HO2S voltage signals. The long term FT makes coarse adjustments in order to maintain Air/Fuel Ratio of 14.7:1. The FT 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. A block of cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term FT diagnostic is based on an average of cells currently being used. The ECM selects the cells based on the engine speed and load. If the ECM detects an excessively rich condition, DTC P0172 sets.

This diagnostic procedure supports the following DTC

DTC P0172 Fuel Trim System Rich

1. DTCs P0030, P0036, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0130, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0201-P0204, P0300, P0442, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0496, P0506, P0507, P1106, P1107, P1133 are not set.
2. The engine is in CL status.
3. The engine coolant temperature (ECT) is between -40 and +127°C (-40 and +260.6°F).
4. The intake air temperature (IAT) is more than -20°C (-4°F).
5. The manifold absolute pressure (MAP) is more than 5 kPa (0.7 psi).
6. The mass air flow (MAF) is more than 0.5 g/s.
7. The vehicle speed is less than 134 km/h (83 mph).
8. The engine speed is between 400-6,000 RPM.
9. The barometric pressure (BARO) is more than 70 kPa (10.2 psi).
10. The fuel level is more than 10 percent.
11. DTC P0172 runs continuously once the above conditions have been met.

1. The long term FT weighted average value is less than a calibrated value.
2. The above condition is present for more than 2 minutes.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

1. Fuel contamination, such as water and alcohol, will affect the FT.
2. The system will go rich if the injectors are supplying too much fuel.
3. Using the scan tool, review the Failure Records. If an intermittent condition is suspected, refer to «Intermittent Conditions»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-troubleshooting-diagnosis__intermittent-conditions) .

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

1. 8: If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be at fault.

DTC P0172

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

This diagnostic procedure supports the following DTCs

1. DTC P0201 Injector 1 Control Circuit
2. DTC P0202 Injector 2 Control Circuit
3. DTC P0203 Injector 3 Control Circuit
4. DTC P0204 Injector 4 Control Circuit

1. The engine is running.
2. The ignition voltage is more than 11.5 volts for 5 seconds.
3. DTC P0201-P0204 run continuously once the above conditions are met.

1. The control module detects an incorrect voltage on the fuel injector control circuit.
2. The above condition is met for 5 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

1. Performing the Fuel Injector Coil Test may help isolate an intermittent condition. Refer to «Fuel Injector Coil Test»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-troubleshooting-diagnosis) .
2. For an intermittent condition, refer to «Intermittent Conditions»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-troubleshooting-diagnosis__intermittent-conditions) .

DTC P0201-P0204

The throttle position (TP) sensors 1 and 2 are located within the throttle body assembly. Each sensor has the following components

1. A 5-volt reference circuit
2. A low reference circuit
3. A signal circuit

This provides the engine control module (ECM) with a signal voltage proportional to throttle plate movement. TP sensor 1 signal voltage at closed throttle is near the 5-volt reference and decreases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is near the low reference and increases as the throttle plate is opened. If the ECM detects that the TP sensor 2 signal voltage is not within the predicted range, DTC P0220 sets.

This diagnostic procedure supports the following DTC

DTC P0220 Throttle Position (TP) Sensor 2 Circuit

1. The ignition switch is in the Crank or Run position.
2. DTC P0641 is not set.
3. The ignition voltage is more than 5.23 volts.
4. DTC P0220 runs continuously when the above conditions are met.

The ECM detects that the TP sensor 2 voltage is less than 0.31 volt or more than 4.7 volts for more than 0.4 second.

1. The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
3. The control module commands the TAC system to operate in the Reduced Engine Power mode.
4. A message center or an indicator displays Reduced Engine Power.
5. Under certain conditions the control module commands the engine OFF.

1. The ECM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic runs and passes.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using a scan tool.

DTC P0220

The throttle position (TP) sensor 1 and sensor 2 are located within the throttle body assembly. Each sensor has the following circuits

1. A 5-volt reference
2. A low reference
3. A signal

This provides the engine control module (ECM) with a signal voltage proportional to throttle plate movement. TP sensor 1 signal voltage at closed throttle is near the 5-volt reference and decreases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is near the low reference and increases as the throttle plate is opened. If the ECM detects that the TP sensor 2 signal voltage is less than the predicted range, DTC P0222 sets.

This diagnostic procedure supports the following DTC

DTC P0222 Throttle Position (TP) Sensor 2 Circuit Low Voltage

1. The ignition switch is in the Crank or Run position.
2. DTC P0641 is not set.
3. The ignition voltage is more than 5.23 volts.
4. DTC P0222 runs continuously when the above conditions are met.

The ECM detects that the TP sensor 2 voltage is less than 0.31 volt for more than 0.4 second.

1. The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
3. The control module commands the TAC system to operate in the Reduced Engine Power mode.
4. A message center or an indicator displays Reduced Engine Power.
5. Under certain conditions the control module commands the engine OFF.

1. The ECM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic runs and passes.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using a scan tool.

DTC P0222

The throttle position (TP) sensor 1 and sensor 2 are located within the throttle body assembly. Each sensor has the following components

1. A 5-volt reference circuit
2. A low reference circuit
3. A signal circuit

This provides the engine control module (ECM) with a signal voltage proportional to throttle plate movement. TP sensor 1 signal voltage at closed throttle is near the 5-volt reference and decreases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is near the low reference and increases as the throttle plate is opened. If the ECM detects that the TP sensor 2 signal voltage is not within the predicted range, DTC P0223 sets.

This diagnostic procedure supports the following DTC

DTC P0223 Throttle Position (TP) Sensor 2 Circuit High Voltage

1. The ignition switch is in the Crank or Run position.
2. DTC P0641 is not set.
3. The ignition voltage is more than 5.23 volts.
4. DTC P0223 runs continuously when the above conditions are met.

The ECM detects that the TP sensor 2 voltage is more than 4.7 volts for more than 0.4 second.

1. The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
3. The control module commands the TAC system to operate in the Reduced Engine Power mode.
4. A message center or an indicator displays Reduced Engine Power.
5. Under certain conditions the control module commands the engine OFF.

1. The ECM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic runs and passes.
2. The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
3. The DTC can be cleared by using a scan tool.

DTC P0223

The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within 2 seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.

The control module monitors the voltage on the fuel pump relay control circuit. If the control module detects an incorrect voltage on the fuel pump relay control circuit, a fuel pump relay control DTC sets.

This diagnostic procedure supports the following DTC

DTC P0230 Fuel Pump Relay Control Circuit

1. The engine speed is more than 400 RPM.
2. The ignition voltage is between 9-18 volts.
3. DTC P0230 runs continuously once the above conditions are met.

1. The control module detects that the commanded state of the driver and the actual state of the control circuit do not match.
2. The above condition is met for a minimum of 2.5 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0230

System Description

The engine control module (ECM) uses information from the crankshaft position (CKP) sensor and the ignition control (IC) module to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the ECM 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 lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the ECM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.

This diagnostic procedure supports the following DTC

DTC P0300 Engine Misfire Detected

1. DTC P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0125, P0128, P0131, P0132, P0171, P0172, P0217, P0315, P0336, P0506, P0601, P0602, P0606, P0641 are not set.
2. The engine speed is between 400-6,500 RPM.
3. The ignition voltage is between 8-18 volts.
4. The engine coolant temperature (ECT) is between -7°C and +122°C (+19°F and +252°F).
5. The fuel level is more than 10 percent.
6. DTC P0300 runs continuously when the above conditions are met.

The ECM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

You must perform the CKP system variation learn procedure before proceeding with this diagnostic table. Refer to CKP System Variation Learn Procedure .

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

1. 2: If the actual CKP variation values are not within the learned values, the misfire counters may increment.
2. 3: P0300, P0340, and P0341 may all be set by similar conditions.

DTC P0300

The crankshaft position (CKP) system variation learn feature is used to calculate reference period errors caused by slight tolerance variations in the crankshaft, and the CKP sensor. The calculated error allows the engine control module (ECM) to accurately compensate for reference period variations. This enhances the ability of the ECM to detect misfire events over a wider range of engine speed and load. The ECM stores the CKP system variation values after a learn procedure has been performed. If the actual CKP variation is not within the CKP system variation compensating values stored in the ECM, DTC P0300 may set. If the ECM detects that the CKP system variation values are not stored in the ECM memory, DTC P0315 sets.

This diagnostic procedure supports the following DTC

DTC P0315 Crankshaft Position (CKP) System Variation Not Learned

1. The engine is running.
2. DTC P0315 runs continuously once the above condition is met.

1. The CKP system variation values are not stored in the ECM memory.
2. The above condition is present for 0.5 second.

1. The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0315

The knock sensor (KS) system enables the engine control module (ECM) 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 ECM adjusts the spark timing based on the amplitude and the frequency of the KS signal. The ECM receives the KS signal through a signal circuit. The KS ground is supplied by the ECM through a low reference circuit. The ECM learns a minimum KS noise level at idle and uses calibrated values for the rest of the RPM range. The ECM should monitor a normal KS signal within the noise channel. If the ECM malfunctions in a manner that will not allow proper diagnosis of the KS system, DTC P0325 will set.

This diagnostic procedure supports the following DTC

DTC P0325 Knock Sensor (KS) Circuit

1. The engine speed is between 1,400-4,000 RPM.
2. DTC P0325 runs continuously when the above conditions are met.

The average KS voltage is less than 0.01 volts or more than 4.9 volts for 8 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0325

The knock sensor (KS) system enables the engine control module (ECM) 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 ECM adjusts the spark timing based on the amplitude and the frequency of the KS signal. The ECM receives the KS signal through a signal circuit. The KS ground is supplied by the ECM through a low reference circuit. The ECM learns a minimum KS noise level at idle and uses calibrated values for the rest of the RPM range. The ECM should monitor a normal KS signal within the noise channel. When the ECM detects a KS signal that varies outside of the noise channel, the ECM will retard the spark timing until the knock goes away. If the ECM is operating on large amounts of spark retard and is unable to eliminate the knock, DTC P0326 will set.

This diagnostic procedure supports the following DTC

DTC P0326 Knock Sensor (KS) Performance

1. The engine speed is between 1,400-4,000 RPM.
2. DTC P0326 runs continuously when the above conditions are met.

1. The KS signal indicates an engine knock is present.
2. The ECM commanded spark retard at a given engine load and speed is more than the calibrated value.
3. The above conditions exist for 8 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0326

The knock sensor (KS) system enables the engine control module (ECM) 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 ECM adjusts the spark timing based on the amplitude and the frequency of the KS signal. The ECM receives the KS signal through a signal circuit. The KS ground is supplied by the ECM through a low reference circuit. The ECM learns a minimum KS noise level at idle and uses calibrated values for the rest of the RPM range. The ECM should monitor a normal KS signal within the noise channel. If the ECM detects the KS signal outside of the noise channel, or the KS signal is not present, DTC P0327 will set.

This diagnostic procedure supports the following DTC

DTC P0327 Knock Sensor (KS) Circuit Low Voltage

1. The engine speed is between 1,400-4,000 RPM.
2. DTC P0327 runs continuously when the above conditions are met.

The KS voltage is not within a calibrated range for a calibrated period of time.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

1. Inspect the KS for physical damage. A KS that is dropped or damaged may cause a DTC to set.
2. Inspect the KS for proper installation. A KS that is loose or over torqued may cause a DTC to set. The KS should be free of thread sealant. The KS mounting surface should be free of burrs, casting flash, and foreign material.
3. The KS must be clear of hoses, brackets, and engine electrical wiring.
4. For an intermittent condition, refer to «Intermittent Conditions»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-troubleshooting-diagnosis__intermittent-conditions) .

DTC P0327

The crankshaft position (CKP) sensor is a variable reluctance sensor. The CKP sensor indicates the crankshaft speed and position. The CKP sensor produces an AC voltage of different amplitude and frequency. The frequency depends on the velocity of the crankshaft. The AC voltage output depends on the CKP and the battery voltage. The CKP sensor works in conjunction with a 7X reluctor wheel attached to the crankshaft. The CKP sensor connects to the engine control module (ECM) through the following circuits

1. The CKP sensor signal
2. The low reference

If the ECM detects an incorrect number of pulses from the CKP sensor, DTC P0335 sets.

This diagnostic procedure supports the following DTC

DTC P0335 Crankshaft Position (CKP) Sensor Circuit

1. DTCs P0340 and P0341 are not set.
2. The engine is cranking or running.
3. The engine speed is less than 6,500 RPM.
4. The MAF Sensor parameter is between 0-3 g/s.
5. DTC P0335 runs continuously once the above condition is met.

1. The ECM detects an incorrect number of CKP pulses during engine cranking for 4 seconds.
2. The ECM detects an incorrect number of CKP pulses while the engine is running for 2 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

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

1. 2: When the ECM enables starter operation, the ECM also initiates the diagnostic test routines for the CKP and camshaft position (CMP) sensors. If the ignition switch is in the start position for more than 4 seconds without the engine cranking, the CKP diagnostics may fail and set this DTC.

DTC P0335

The crankshaft position (CKP) sensor is a variable reluctance sensor. The CKP sensor indicates the crankshaft speed and position. The CKP sensor produces an AC voltage of different amplitude and frequency. The frequency depends on the velocity of the crankshaft. The AC voltage output depends on the crankshaft position and the battery voltage. The CKP sensor works in conjunction with a 7X reluctor wheel attached to the crankshaft. The CKP sensor connects to the engine control module (ECM) through the following circuits

1. The CKP sensor signal
2. The low reference

If the ECM detects an excessive number of resyncs from the CKP sensor, DTC P0336 sets.

This diagnostic procedure supports the following DTC

DTC P0336 Crankshaft Position (CKP) Sensor Performance

1. The engine is cranking or running.
2. DTC P0336 runs continuously once the above condition is met.

The ECM detects five CKP resyncs within 10 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0336

This ignition system does not use a conventional camshaft position (CMP) sensor that detects valve train position. The ignition control module (ICM) detects when #1 or #3 cylinder has fired on the cylinders 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 engine control module (ECM) 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 ECM can accurately sequence the fuel injectors. If the ECM does not receive a CMP signal from the ICM, DTC P0340 sets.

1. The engine is running.
2. The manifold absolute pressure (MAP) is more than 30 kPa.

The ECM does not detect any change in the CMP sensor signal for 107 crankshaft revolutions when the MAP is at 30 kPa or more.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

1. An intermittent crank signal will result in an interrupted cam signal and may set this DTC.
2. The following conditions may cause this DTC to set: High resistance in the #1 secondary ignition system Low resistance in the #4 secondary ignition system Corroded or loose #1 or #4 secondary ignition components
3. If this DTC is determined to be intermittent, refer to «Intermittent Conditions»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-troubleshooting-diagnosis__intermittent-conditions) .

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

1. 4: If CYL #1 and/or CYL #4 Misfire Counters are incrementing there is a condition within the secondary ignition system that effects the camshaft position signal circuit.
2. 6: The ECM supplies 5 volts on the camshaft position signal circuit. This step determines if the ECM is supplying the correct voltage on the circuit.

DTC P0340

This ignition system does not use a conventional camshaft position (CMP) sensor that detects valve train position. The ignition control module (ICM) detects when #1 or #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 CMP signal to the engine control module (ECM) 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 ECM can accurately sequence the fuel injectors. If the ECM receives an intermittent CMP signal from the ICM, DTC P0341 sets.

The engine is running.

The ECM detects more than 11 extra CMP signal transitions when the manifold absolute pressure (MAP) is greater than 30 kPa.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

1. If DTC P0336 is set, diagnose that DTC first. An intermittent fault in the CKP circuit will cause the ECM to resync the cam and may set DTC P0341.
2. An intermittent short to voltage on the CMP signal circuit can set this DTC. A direct short to voltage on the CMP signal circuit will set DTC P0340, as there will be no change in the cam signal input.
3. The following conditions may set this DTC: High resistance in the #1 secondary ignition system Low resistance in the #4 secondary ignition system Corroded or loose #1 or #4 secondary ignition components Harness being routed too close to the secondary ignition components, relays, motors
4. If this DTC is determined to be intermittent, refer to «Intermittent Conditions»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-troubleshooting-diagnosis__intermittent-conditions) .

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

1. 3: This step determines if DTC P0341 is the result of a hard malfunction or an intermittent condition.

DTC P0341

A 3-way catalytic converter (TWC) controls 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 water vapor and carbon dioxide (CO2), and will reduce the NOx, converting the NOx into nitrogen. The catalytic converter also stores oxygen. The engine control module (ECM) monitors this process by using a heated oxygen sensor (HO2S) which is in the exhaust stream past the TWC. 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 ECM monitors the catalyst efficiency by first allowing the catalyst to heat, then waiting for a stabilization period while the engine is idling. Then, the ECM adds and removes 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 HO2S 1. When the HO2S 2 response is close to that of the HO2S 1, the oxygen storage capability or efficiency of the catalyst may be degraded below an acceptable threshold. If the ECM detects the degraded condition DTC P0420 sets.

This diagnostic procedure supports the following DTC

DTC P0420 Catalyst System Low Efficiency

1. DTCs P0031, P0037, P0038, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0137, P0138, P0140, P0141, P0171, P0172, P0300, P0326, P0327, P0336, P0340, P0341, P0500 (manual transmission only), P0506, P0507, P0601, P0602, P0606, P0641, P0722, P0723, P1133, P1134 are not set.
2. The engine has been running more than 9.5 minutes after the throttle has moved.
3. The vehicle is in a Closed Loop operation.
4. The vehicle has been driven at more than 1,200 RPM for more than 30 seconds.
5. The Short Term Fuel Trim (FT) is between -5 and +5 percent.
6. The catalytic temperature is more than 375°C (707°F), and less than 750°C (1,382°F).
7. An automatic transmission must remain in drive.
8. The vehicle speed is less than 1.6 km/h (1 mph).
9. The engine must be at a stabilized idle.
10. The manifold absolute pressure (MAP) sensor variation is less than 6 kPa.
11. This diagnostic attempts one test during each valid idle period once the above conditions have been met.
12. This diagnostic attempts up to 6 tests during each drive cycle.

1. The ECM has determined the catalyst efficiency has degraded below a calibrated threshold.
2. This diagnostic may conclude in as few as one test attempt. However, this diagnostic may require as many as 18 test attempts, which would require at least 3 drive cycles. Each test attempt may conclude within approximately 7 minutes.

1. The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

The catalyst test may abort due to a change in the engine load. Allow the engine to return to a stabilized idle. An automatic transmission must remain in Drive. A manual transmission is shifted into Neutral. Do not touch the accelerator pedal, steering wheel or HVAC controls while a catalyst test is in progress.

Certain conditions may cause a catalytic converter to degrade. These conditions may include the following conditions

1. An engine misfire
2. High engine oil or high coolant consumption
3. Retarded spark timing
4. A weak spark
5. A lean fuel mixture
6. A rich fuel mixture
7. A damaged oxygen sensor wiring harness

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

1. 6: This step includes inspections for conditions that can cause the TWC to appear degraded. Before you proceed with this table, repair any conditions that you find.

DTC P0420

This diagnostic tests the evaporative emission (EVAP) system for a small leak when the key is turned OFF and the correct conditions are met.

Heat from the exhaust system is transferred into a vehicle fuel tank while the vehicle is operating. When the vehicle is turned OFF and the EVAP system is sealed, a change in the fuel tank vapor temperature occurs, which results in corresponding pressure changes in the fuel tank vapor space. This change is monitored by the control module using the fuel tank pressure sensor input. The control module then makes a judgement on the integrity of the system. With a 0.51 mm (0.02 in) leak in the system, the amount of pressure change observed is significantly less than that of a sealed system.

If the control module detects a pressure change less than a calibrated amount, DTC P0442 sets.

This diagnostic procedure supports the following DTC

DTC P0442 Evaporative Emissions (EVAP) System Small Leak Detected

1. Before the engine control module (ECM) can report DTC P0442 failed, DTCs P0443, P0446, P0449, P0452, P0453, P0455, and P0496 must run and pass.
2. DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0125, P0128, P0446, P0452, P0453, P0455, P0496, P0502, P0601, P0602, P0606, P0641, P2610 are not set.
3. The diagnostic runs once after a cold start drive cycle.
4. The start-up intake air temperature (IAT) is between 4-30°C (39-86°F).
5. The start-up engine coolant temperature (ECT) is less than 30°C (86°F).
6. The start-up IAT and ECT are within 8°C (15°F).
7. The barometric pressure (BARO) is more than 74 kPa.
8. The ambient air temperature is between 2-32°C (36-90°F).
9. The engine run time minimum is 10 minutes.
10. The vehicle has traveled more than 5 kilometers (3 miles) this trip.
11. The ECT is more than 70°C (158°F).
12. The fuel level is between 15-85 percent.
13. The ignition is OFF.
14. A refueling event is not detected.
15. DTC P0442 runs once per drive cycle when the above conditions are met.
16. One test occurs at ignition OFF after a drive cycle, and may require up to 45 minutes to complete. No more than 2 tests per day are allowed.

1. The control module detects a pressure change that is less than a calibrated amount.
2. Five to 12 tests must be completed to report a Fail with up to 17 hours between tests.

1. The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

1. To help locate intermittent leaks, use the J 41413-200 Evaporative Emission System Tester (EEST) to introduce smoke into the EVAP system. Move all EVAP components while observing smoke with a High Intensity White Light.
2. A leak in the EVAP system can be verified by use of the flow meter on the J 41413-200 . Refer to the J 41413-200 operation manual for flow meter use instructions.
3. To improve the visibility of the smoke exiting the EVAP system, observe the suspected leak area from different angles with a High Intensity White Light.
4. A condition may exist where a leak in the EVAP system only exists under a vacuum condition. By using the scan tool Purge/Seal function to create a vacuum, seal the system and observe the FTP parameter for vacuum decay, this type of leak may be detected.
5. For intermittent conditions, refer to «Intermittent Conditions»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-troubleshooting-diagnosis__intermittent-conditions) .

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

1. 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.
2. 5: This step verifies that repairs are complete and that no other condition is present.

DTC P0442

An ignition voltage is supplied directly to the evaporative emission (EVAP) canister purge solenoid valve. The EVAP canister purge solenoid valve is pulse width modulated (PWM). The scan tool displays the amount of ON time as a percentage. The control module monitors the status of the driver. The control module controls the EVAP canister purge solenoid valve ON time by grounding the control circuit via an internal switch called a driver. If the control module detects an incorrect voltage for the commanded state of the driver, this DTC sets.

This diagnostic procedure supports the following DTC

DTC P0443 Evaporative Emission (EVAP) Purge Solenoid Control Circuit

1. The ignition is ON.
2. The system voltage is between 6-18 volts.
3. DTC P0443 runs continuously once the above conditions are met.

1. The control module detects that the commanded state of the driver and the actual state of the control circuit do not match.
2. The above conditions are present for a minimum of 12 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

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

1. 2: This step tests if the concern is active. The EVAP canister purge solenoid valve is PWM. You should hear a clicking sound when the EVAP canister purge solenoid valve is commanded to 50 percent. The clicking sound should stop when the EVAP canister purge solenoid valve is commanded to 0 percent. The rate at which the valve cycles should increase when the commanded state is increased, and decrease when the commanded state is decreased.
2. 5: This step verifies that the control module is providing ground to the EVAP canister purge solenoid valve.
3. 6: This step tests if a ground is constantly being applied to the EVAP canister purge solenoid valve.

DTC P0443

This DTC tests the evaporative emission (EVAP) system for a restricted or blocked EVAP vent path. The control module commands the EVAP canister purge solenoid valve Open and the EVAP canister vent solenoid valve Closed. This allows vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the EVAP canister purge solenoid valve Closed and the EVAP canister vent solenoid valve Open. The control module monitors the fuel tank pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near 0 inches 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 solenoid valves.

DTC P0446

This diagnostic procedure supports the following DTC

DTC P0446 Evaporative Emissions (EVAP) Vent System Performance

1. DTCs P0030, P0036, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0220, P0442, P0443, P0449, P0452, P0453, P0455, P0502, P0562, P0563, P0641, P0651, and P1133, P1134 are not set.
2. The ignition voltage is between 11-18 volts.
3. The barometric pressure (BARO) is more than 74 kPa.
4. The fuel level is between 15-85 percent.
5. The start-up engine coolant temperature (ECT) is between 4-30°C (39-86°F).
6. The start-up intake air temperature (IAT) is between 4-30°C (39-86°F).
7. The start-up ECT and IAT are within 8°C (14.4°F) of each other.
8. The vehicle speed sensor (VSS) is less than 137 km/h (85 mph).
9. The purge solenoid valve is enabled.
10. DTC P0446 runs once per trip when the above conditions have been met.

1. The FTP sensor is more than 8 inches H2O for 2 seconds during the 13 minute test. OR The FTP is less than -2.5 inches H2O or more than +5 inches H2O for 3 seconds after a cold start ignition ON.
2. The fuel tank vacuum is greater than a calibrated amount for a calibrated period of time.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

1. The EVAP system tests run when the engine is first started and meets the Conditions for Running the DTC. An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP canister vent inlet, or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill condition.
2. An EVAP canister, vent hose, or vent solenoid valve that has restricted flow may cause this DTC to set. Using a purge solenoid command with a scan tool will allow vacuum to be applied to the system instead of pressure. With the engine running, the EVAP canister vent solenoid valve open, and the EVAP canister purge solenoid valve commanded to 100 percent, the fuel tank vacuum should not increase to more than 5 inches H2O.
3. An EVAP canister filter that is restricted can cause this DTC to set. Refer to «Evaporative Emission (EVAP) Canister Filter Replacement»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-introduction) and «Evaporative Emission (EVAP) System Cleaning»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-introduction) .
4. Disconnecting one component at a time while the EVAP system is under flow will help to pinpoint a restriction in the system.
5. Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
6. For intermittent conditions, refer to «Intermittent Conditions»(/chevrolet/cobalt/i-2004-2010/remont/testing-diagnostics/#engine-controls-22l-troubleshooting-diagnosis__intermittent-conditions) .

DTC P0446

A battery voltage is supplied to the evaporative emission (EVAP) canister vent solenoid valve. The control module grounds the EVAP canister vent solenoid valve control circuit to close the valve by means of an internal switch called a driver. The scan tool displays the commanded state of the EVAP canister vent solenoid valve as ON or OFF. The control module monitors the status of the driver. If the control module detects an incorrect voltage for the commanded state of the driver, 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 vent solenoid valve.

DTC P0449

This diagnostic procedure supports the following DTC

DTC P0449 Evaporative Emission (EVAP) Vent Solenoid Control Circuit

1. The ignition is ON.
2. The system voltage is between 6-18 volts.
3. DTC P0449 runs continuously once the above conditions are met.

1. The control module detects that the commanded state of the driver and the actual state of the control circuit do not match.
2. The above conditions are present for a minimum of 12 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

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

1. 2: Listen for a click when the valve operates. Verify that both the ON and the OFF states are commanded.
2. 5: This step verifies that the control module is providing ground to the EVAP canister vent solenoid valve.
3. 6: This step tests if the EVAP canister vent solenoid valve control circuit is grounded.

DTC P0449

See also:
• Engine Controls Schematics
• Engine Controls Connector End Views
• Engine Control Module (ECM) Connector End Views
• Diagnostic System Check - Vehicle
• Scan Tool Data List
• Testing for Intermittent Conditions and Poor Connections
• Circuit Testing
• Wiring Repairs
• Silicon Contamination of Heated Oxygen Sensors Notice
• DTC P0106
• Fuel System Diagnosis
• Control Module References
• Diagnostic Trouble Code (DTC) List - Vehicle
• Connector Repairs
• Probing Electrical Connectors
• Intermittent Conditions
• Altitude vs Barometric Pressure
• Symptoms - Engine Mechanical
• Special Tools
• CKP System Variation Learn Procedure
• Crankcase Ventilation System Inspection/Diagnosis
• Ground Distribution Schematics
• Restricted Exhaust
• Spark Plug Inspection
• Crankshaft and Bearings Cleaning and Inspection
• Detonation/Spark Knock
• Measuring Frequency
• Symptoms - Engine Electrical
• Using Connector Test Adapters
• Exhaust Leakage
• Road Test Caution
• Evaporative Emissions (EVAP) Hose Routing Diagram
• Testing for Short to Ground
• DTC P0420