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-P0308 correspond to cylinders 1-8. If the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder will set.
Conditions for Running the DTC
| • | DTCs P0102, P0103, P0315, P0335, P0336, P0365, P0366, or P0390 are not set. |
| • | The engine speed is between 500-6,496 RPM. |
| • | The engine load is more than 0 percent. |
| • | The torque management is not active. |
| • | The fuel level is more than 10.5 liters (3 gallons) |
| • | The antilock brake (ABS) system is not active. |
| • | The ECM is not receiving a rough road signal. |
| • | The ECM is not in fuel shut-off or decel mode. |
| • | The engine coolant temperature (ECT) is more than -7.5°C (18.5°F). |
Conditions for Setting the DTC
The ECM is detecting 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) 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 ECM turns OFF the MIL after 3 consecutive drive trips that the diagnostic runs and does not fail within the same conditions that the DTC last failed. |
| • | A History DTC clears after 40 consecutive warm-up cycles if no failures report by this diagnostic or any other emission related diagnostic. |
| • | The DTC can be cleared 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. |
| • | If there are multiple misfires on only one bank, inspect the fuel injector and ignition coil, power and ground circuits for that bank. Refer to Engine Controls Schematics . |
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 | |||||||||||||||
|
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 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 16 | Go to Step 6 | ||||||||||||||
6 |
Did the spark tester spark on all cylinders? | -- | Go to Step 7 | |||||||||||||||
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 15 | Go to Step 12 | ||||||||||||||
9 | Are the spark plugs oil or coolant fouled? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical | Go to Step 10 | ||||||||||||||
10 | Are the spark plugs gas fouled? | -- | Go to Step 13 | Go to Step 11 | ||||||||||||||
11 | Do the spark plugs show any signs of being cracked, worn, or improperly gapped? | -- | Go to Step 14 | 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 16 | Go to Symptoms - Engine Mechanical in Engine Mechanical | ||||||||||||||
13 | Perform the fuel system diagnosis. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 16 | Go to Symptoms - Engine Mechanical in Engine Mechanical | ||||||||||||||
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 plugs. 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 the DTC run and pass? | 2,500 RPM | Go to Step 18 | Go to DTC P0420 or P0430 | ||||||||||||||
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 |
