System Description
The powertrain control module (PCM) 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 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 lamp (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.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P0301 Cylinder 1 Misfire Detected |
| • | DTC P0302 Cylinder 2 Misfire Detected |
| • | DTC P0303 Cylinder 3 Misfire Detected |
| • | DTC P0304 Cylinder 4 Misfire Detected |
| • | DTC P0305 Cylinder 5 Misfire Detected |
| • | DTC P0306 Cylinder 6 Misfire Detected |
Conditions for Running the DTC
| • | DTCs P0013, P0014, P0016, P0105, P0106, P0107, P0108, P0117, P0118, P0120, P0122, P0123, P0125, P0128, P0218, P0220, P0315, P0336, P0340, P0341, P0502, P0503, P1345, P2125, P2135 are not set. |
| • | The engine speed is between 450-5,000 RPM. |
| • | The ignition voltage is between 10-18 volts. |
| • | The engine coolant temperature (ECT) is between -7 and +130°C (+19 and +266°F). |
| • | The fuel level is more than 10 percent. |
| • | The throttle angle is steady within 1 percent. |
| • | The antilock brake system (ABS) is not active. |
| • | The transmission is not changing gears. |
| • | The A/C clutch is not changing states. |
| • | The PCM is not in fuel shut-off or decel fuel cut-off mode. |
| • | The PCM is not receiving a rough road signal. |
| • | DTC P0301, P0302, P0303, P0304, P0305, P0306 run continuously when the above conditions are met. |
Conditions for Setting the DTC
The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.
Diagnostic Aids
You must perform the CKP system variation learn procedure before proceeding with this diagnostic table. Refer to Crankshaft Position System Variation Learn .
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. |
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 - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
Are any of the Misfire current counters incrementing? | -- | Go to Step 3 | Go to Intermittent Conditions | |
3 | Are any other DTCs set? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | Go to Step 4 |
4 | Can any abnormal engine noise be heard? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical - 4.2L | Go to Step 5 |
5 |
Important: Not grounding the ignition coil may cause an erratic spark. Does the spark tester spark? | -- | Go to Step 7 | Go to Step 6 |
6 | Inspect the affected cylinder spark plug boot for a missing or damaged ignition coil spring. Did you find and correct the condition? | -- | Go to Step 15 | |
7 |
Does the spark plug appear to be OK? | -- | Go to Step 8 | Go to Step 9 |
8 |
Did the misfire move with the spark plug? | -- | Go to Step 14 | Go to Step 12 |
9 | Is the spark plug oil or coolant fouled? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical- 4.2L | Go to Step 10 |
10 | Is the spark plug gas fouled? | -- | Go to Step 12 | Go to Step 11 |
11 | Did the spark plug show any signs of being cracked, worn, or improperly gapped? | -- | Go to Step 13 | Go to Step 12 |
12 | Perform the fuel injector coil test. Refer to Fuel Injector Solenoid Coil Test . Did you find and correct the condition? | -- | Go to Step 15 | Go to Symptoms - Engine Mechanical in Engine Mechanical- 4.2L |
13 | Replace or gap the spark plug. Refer to Spark Plug Replacement . Did you complete the action? | -- | Go to Step 15 | -- |
14 | Replace the faulty spark plug. Refer to Spark Plug Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- |
15 | Was the customer concern the malfunction indicator lamp (MIL) flashing? | -- | Go to Step 16 | Go to Step 17 |
16 |
Does the DTC run and pass? | 2,500 RPM | Go to Step 17 | Go to DTC P0420 |
17 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 18 |
18 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
