Circuit Description
The powertrain control module (PCM) times the intervals between each pulse of the crankshaft position sensor and compares each time interval with the other 8 to determine when an excessive change in crankshaft speed has occurred. This pulse is generated from a reluctor wheel located on the front of the crankshaft. If the crankshaft speed is less than an expected amount, the PCM will increase the amount of fuel needed to correct the misfire. If the amount of fuel exceeds the calibrated value, the PCM will interpret this as a misfire and set the diagnostic trouble code (DTC). The misfire diagnostic is used only to identify a weak cylinder needing additional fuel. This diagnostic will only run once per ignition cycle.
Conditions for Running the DTC
| • | The engine coolant temperature (ECT) is more than 56°C (132°F). |
| • | The engine is idling for 90 seconds. |
Conditions for Setting the DTC
| • | The fuel adjustment is more than the calibrated value. |
| • | Multiple engine misfires are detected. |
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
The most likely cause for this DTC is the following:
| • | A mechanical failure causing low cylinder compression. |
| • | A fuel leak at the high pressure fuel injection lines or injection nozzles. |
| • | A fuel injection nozzle stuck closed. |
If an injection nozzle is suspected, the nozzle can be transferred to another cylinder to determine if the DTC follows the nozzle.
After the repair has been performed, it may take approximately 30 seconds for the vehicle to return to a stable idle.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step will help identify a suspected cylinder.
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This step will identify an area with the most likely cause of failure.
Step | Action | Yes | No | ||||
|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |||||
Does the RPM drop when the suspected cylinder is cancelled? | Go to Step 3 | Go to Step 4 | |||||
3 | The DTC is intermittent. If no additional DTCs are stored, refer to diagnostic aids. If any additional DTCs were stored, refer to the applicable DTC tables first. Are any additional DTCs stored? | Go to Diagnostic Aids | |||||
Check for basic engine mechanical or fuel delivery problems in that cylinder:
Did you find and correct the condition? | Go to Step 6 | Go to Step 5 | |||||
5 | Replace the fuel injection pump. Refer to Fuel Injection Pump Replacement . Did you complete the replacement? | Go to Step 6 | -- | ||||
6 |
Does the DTC run and pass? | Go to Step 7 | Go to Step 2 | ||||
7 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK |
