System 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 preset. DTCs P0301-P0306 correspond to cylinders 1-6. 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 emissions levels to exceed mandated standards, DTC P0300 will set.
Conditions for Running the DTC
| • | DTC P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0125, P0128, P0220, P0315, P0335, P0336, P0341, P0342, P0343, P0502, P0503, P1114, P1115, P1120, P1258 are not set. |
| • | The engine speed is between 520-6,520 RPM. |
| • | The intake air temperature (IAT) is more than -30°C (-22°F). |
| • | The throttle angle is steady within 1 percent. |
| • | The antilock brake system (ABS) and is not active. |
| • | The transmission is not changing gears. |
| • | The A/C clutch is not changing states. |
| • | The ECM is not in fuel shut-off or decel fuel cut-off mode. |
| • | The ECM is not receiving a rough road signal. |
Conditions for Setting the DTC
The ECM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | 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
| • | 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
| • | Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration: |
| - | Thickness variation of the brake rotors--Refer to Symptoms - Hydraulic Brakes in Hydraulic Brakes. |
| - | The drive shaft not balanced--Refer to Vibration Analysis - Driveline in Vibration Diagnosis and Correction. |
| - | Worn or damaged accessory drive belt--Refer to Symptoms - Engine Mechanical in Engine Mechanical. |
| • | There may be more or less cylinders actually misfiring than indicated by the scan tool. |
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||
Are any of the Misfire current counters incrementing? | -- | Go to Step 3 | Go to Diagnostic Aids | |||||||||||||
3 | Are any other DTCs set? | -- | Go to Step 4 | |||||||||||||
4 | Can any abnormal engine noise be heard? | -- | Go to Step 5 | |||||||||||||
5 | Are there multiple misfires indicated on only one bank? | -- | Go to Step 6 | |||||||||||||
6 | Are there 2 cylinders misfiring on only one bank? | -- | Go to Step 7 | |||||||||||||
7 | Inspect the following components:
Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8 | ||||||||||||
8 | Perform the fuel system diagnosis. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 9 | |||||||||||||
9 | Was the customer concern the malfunction indicator lamp (MIL) flashing? | -- | Go to Step 10 | Go to Step 11 | ||||||||||||
10 |
Does the DTC run and pass? | 2,500 RPM | Go to Step 11 | Go to DTC P0421 or P0431 | ||||||||||||
11 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 12 | ||||||||||||
12 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
