Description
The engine control module (ECM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor in order 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 3-way catalytic converter damage. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for catalytic converter damage are present. DTCs P0301 through P0306 correspond to cylinders 1 through 6. If the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder will set. If the misfire rate is sufficient to cause emission levels to exceed a predetermined value, this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0300 Engine Misfire Detected
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0121, P0122, P0123, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P0335, P0336, P0337, P0341, P0342, P1320, and P1321 are not set. |
| • | The engine speed is between 500-6,500 RPM and steady. |
| • | The engine coolant temperature (ECT) is more than -7.5°C (18.5°F). |
| • | The barometric pressure (BARO) is more than 74.5 kPa. |
| • | The ignition 1 voltage is more than 11 volts. |
| • | The throttle angle and mass air flow (MAF) are steady. |
| • | The torque management is not active. |
| • | The antilock brake system/traction control system (ABS/TCS) is not active. |
| • | The ECM is not receiving a rough road signal. |
| • | The ECM is not in fuel cut-off or decel cut-off mode. |
| • | The transmission is not changing gears. |
| • | The A/C clutch is not changing states. |
| • | DTC P0300 runs continuously when the above conditions are met. |
Conditions for Setting the DTC
The ECM detects a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed mandated standards.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | 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. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
| • | A misfire DTC could be caused by an excessive vibration from sources other than the engine. Inspect for the following possible sources: |
| - | A tire or wheel that is out of round or out of balance |
| - | Variable thickness brake rotors |
| - | An unbalanced drive shaft |
| - | Certain rough road conditions |
| - | A damaged accessory drive component or belt |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Step | Action | Values | Yes | No | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | |||||||||||||||||
|
Important: The engine may only misfire when the engine is under a load. An engine load may be necessary to verify the condition.
Did DTCs P0300, or P0301-P0306 set? | 1,500 RPM | Go to Step 4 | Go to Step 3 | |||||||||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||||||||||
4 |
Important: Excessive vibration from other sources than the engine, or a mechanical engine condition can cause a misfire DTC to set. For example, an accessory drive belt could cause this condition. Is the engine misfiring? | -- | Go to Step 5 | Go to Symptoms - Engine Mechanical in Engine Mechanical-2.5L (LBK) | ||||||||||||||||
5 | Observe the DTC Info with a scan tool. Is DTC P0101, P0102, P0103, P0106, P0107, P0108, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P0335, P0336, P0337, P0341, P0342, P0351-P0356, P1320, or P1321 also set? | -- | Go to Step 6 | |||||||||||||||||
6 | Is there an engine mechanical noise? | Go to Symptoms - Engine Mechanical in Engine Mechanical-2.5L (LBK) | Go to Step 7 | |||||||||||||||||
7 | Is there more than one misfire DTC set? | -- | Go to Step 8 | Go to DTC P0301-P0306 | ||||||||||||||||
8 | Is there any HO2S DTCs set? | -- | Go to Step 9 | |||||||||||||||||
9 |
Did you find and correct the condition? | -- | Go to Step 10 | Go to Symptoms - Engine Mechanical in Engine Mechanical-2.5L (LBK) | ||||||||||||||||
10 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 11 | ||||||||||||||||
11 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
