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 Descriptor
This diagnostic procedure supports the following DTC:
DTC P0300 Engine Misfire Detected
Conditions for Running the DTC
| • | DTCs P0013, P0014, P0016, P0106, P0107, P0108, P0117, P0118, P0120, P0125, P0128, P0218, P0220, P0315, P0336, P0340, P0341, P0365, P0366, P0502, P0503, P1114, P1115, P2125, P2135 are not set. |
| • | The engine is running. |
| • | The ignition voltage is between 10-18 volts. |
| • | The engine coolant temperature (ECT) is between -7 and +130°C (+19 and +266°F). |
| • | The throttle angle is steady. |
| • | The A/C compressor clutch is not changing state. |
| • | The exhaust gas recirculation (EGR) flow test is inactive. |
| • | The fuel level is above 10 percent. |
| • | The fuel cut-off or decel fuel cut-off (DFCO) mode is not active. |
| • | The PCM is not receiving a rough road signal. |
| • | DTC P0300 runs 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.
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 . |
| - | The drive shaft not balanced--Refer to Vibration Analysis - Driveline . |
| - | Worn or damaged accessory drive belt--Refer to Symptoms - Engine Mechanical . |
| • | There may be more or less cylinders actually misfiring than indicated by the scan tool. |
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 - Vehicle? | -- | Go to Step 2 | |||||||||||||
|
Important: You must perform the crankshaft position (CKP) system variation learn procedure before proceeding with this diagnostic table. Refer to Crankshaft Position System Variation Learn .
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 | Inspect the following components:
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 6 | ||||||||||||
6 |
Important: Not grounding the ignition coil may cause an erratic spark. Does the spark tester spark? | -- | Go to Step 8 | Go to Step 7 | ||||||||||||
7 | 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 | |||||||||||||
8 |
Does the spark plug appear to be OK? | -- | Go to Step 9 | Go to Step 10 | ||||||||||||
9 |
Did the misfire move with the spark plug? | -- | Go to Step 15 | Go to Step 13 | ||||||||||||
10 | Is the spark plug oil or coolant fouled? | -- | Go to Step 11 | |||||||||||||
11 | Is the spark plug gas fouled? | -- | Go to Step 13 | Go to Step 12 | ||||||||||||
12 | Did the spark plug show any signs of being cracked, worn, or improperly gapped? | -- | Go to Step 14 | Go to Step 13 | ||||||||||||
13 | Perform the fuel injector coil test. Refer to Fuel Injector Diagnosis . Did you find and correct the condition? | -- | Go to Step 15 | |||||||||||||
14 | Replace or gap the spark plug. Refer to Spark Plug Replacement . Did you complete the action? | -- | Go to Step 16 | -- | ||||||||||||
15 | Replace the faulty spark plug. Refer to Spark Plug Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||||||||
16 | Was the customer concern the malfunction indicator lamp (MIL) flashing? | -- | Go to Step 17 | Go to Step 18 | ||||||||||||
17 |
Does DTC P0420 run and pass? | 2,500 RPM | Go to Step 18 | Go to DTC P0420 | ||||||||||||
18 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 19 | ||||||||||||
19 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
