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, DTC P0300 will set.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0300 Engine Misfire Detected
Conditions for Running the DTC
| • | DTCs P0121, P0122, P0123, P0222, P0223, P0335, P0341, P0342, P0343, P0440, P0443, P0444, or P0445 are not set. |
| • | The engine speed is between 480-6,520 RPM. |
| • | The torque management is not active. |
| • | The antilock brake system (ABS) 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 has been running for longer than 5 seconds. |
| • | The intake air temperature (IAT) is more than -30°C (-22°F). |
| • | DTC P0300 runs continuously once the above conditions are met. |
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, or to damage the catalytic converter for a monitoring period ranging between 2 seconds and approximately 30 minutes.
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 . |
| • | Worn or damaged accessory drive belt--Refer to Symptoms - Engine Mechanical . |
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 | ||||||||||||||
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 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 | Go to Step 5 | ||||||||||||||
5 | Inspect the following components:
Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 6 | ||||||||||||||
6 |
Important: DO NOT remove the connector from the IC module assembly. Does the spark tester spark? | -- | Go to Step 8 | Go to Step 7 | ||||||||||||||
7 | Inspect the affected cylinders spark plug boots for missing or damaged ignition coil spring. Did you find and correct the condition? | -- | Go to Step 17 | |||||||||||||||
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 16 | Go to Step 13 | ||||||||||||||
10 | Are the spark plugs oil or coolant fouled? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical | Go to Step 11 | ||||||||||||||
11 | Are the spark plugs gas fouled? | -- | Go to Step 14 | Go to Step 12 | ||||||||||||||
12 | Do the spark plugs show any signs of being cracked, worn, or improperly gapped? | -- | Go to Step 15 | Go to Step 13 | ||||||||||||||
13 | Perform the fuel injector coil test. Refer to Fuel Injector Solenoid Coil Test . Did you find and correct the condition? | -- | Go to Step 17 | Go to Symptoms - Engine Mechanical in Engine Mechanical | ||||||||||||||
14 | Perform the fuel system diagnosis. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 17 | Go to Symptoms - Engine Mechanical in Engine Mechanical | ||||||||||||||
15 | Replace or gap the spark plug. Refer to Spark Plug Replacement . Did you complete the action? | -- | Go to Step 17 | -- | ||||||||||||||
16 | Replace the faulty spark plugs. Refer to Spark Plug Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||||
17 | Was the customer concern the malfunction indicator lamp (MIL) flashing? | -- | Go to Step 18 | Go to Step 19 | ||||||||||||||
18 |
Does the DTC run and pass? | 2,500 RPM | Go to Step 19 | Go to DTC P0421 or P0431 | ||||||||||||||
19 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 20 | ||||||||||||||
20 | 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 |
