Circuit 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 present. DTCs 301 through 306 correspond to cylinders 1 through 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
| • | DTCs P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336, P0337, P0338, P0341, P0342, P0343, P0440, P0442, P0443, P0444 or P0445 are not set. |
| • | The engine speed is between 520-6,520 RPM. |
| • | The torque management is not active. |
| • | The anti-lock brake/traction control (ABS/TC) system is not active. |
| • | The ECM is not receiving a rough road signal. |
| • | The fuel cut-off is not active, including the traction control, the deceleration, the high speed/RPM. |
| • | The engine has been running for longer than 5 seconds. |
| • | The air intake temperature (IAT) is more than -8°C (17°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 three 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 forty 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
A Misfire DTC could be caused by an excessive vibration from sources other than the engine. Check for the following possible sources:
| • | A tire or wheel that is out of round or out of balance |
| • | Variable thickness brake rotor or drum |
| • | An unbalanced drive shaft |
| • | Certain rough road conditions |
| • | a damaged accessory drive belt |
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||
2 |
Are any of the misfire current counters incrementing? | -- | Go to Step 3 | Go to Diagnostic Aids | ||||||||
3 | Are any DTCs from P0201-P0206 also set? | -- | Go to Step 4 | |||||||||
4 | Are any DTCs from P0301-P0306 also set? | -- | Go to Step 5 | |||||||||
5 | Does the scan tool indicate that any HO2S voltage parameters are fixed below the specified value? | 200 mV | Go to Step 6 | |||||||||
6 | Does the scan tool indicate that any HO2S voltage parameters are fixed above the specified value? | 900 mV | Go to DTC P0132 or P0152 | Go to Step 7 | ||||||||
7 |
Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 | ||||||||
8 |
Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 | ||||||||
9 |
Did you find and correct the condition? | -- | Go to Step 10 | Go to Symptoms - Engine Mechanical in Engine Mechanical | ||||||||
10 |
Does the DTC run and pass? | -- | Go to Step 11 | Go to Step 2 | ||||||||
11 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK |
