System Description
The powertrain control module (PCM) monitors both the crankshaft and camshaft position in order to detect engine misfire. The PCM looks for the rapid decrease in crankshaft speed associated with engine misfire once every 100 camshaft revolutions. The PCM may require that several consecutive misfire conditions are detected before storing this DTC and illuminating the MIL. Under light misfire conditions, the PCM may require more than one trip to set this DTC. Under severe misfire, the PCM flashes the MIL. A flashing MIL signals that a misfire capable of damaging the catalytic converter is detected. The torque converter clutch is disabled momentarily to determine if the misfire was due to a rough road condition (automatic transmission only).
Conditions for Running the DTC
| • | DTCs P0105, P0107, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0502, P0503, P0506, P0507, P0601, P0740, P0742, P1133, and P1621 are not set. |
| • | The engine speed is between 469 RPM and 5900 RPM. |
| • | The battery voltage is between 9 volts and 17 volts. |
| • | The engine coolant temperature (ECT) is between -7°C (20°F) and 123°C (254°F). |
| • | The engine has been running more than 5 seconds. |
| • | The throttle position (TP) has not increased more than 8 percent in 1 second. |
| • | The TP has not decreased more than 1.5 percent in 1 second. |
Conditions for Setting the DTC
The misfire total is more than 8 counts.
Action Taken When the DTC Sets
The malfunction indicator lamp (MIL) will illuminate if the fault is active within the same conditions for two out of eighty ignition cycles when there is misfire.
OR
The MIL will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.
OR
| • | The MIL will illuminate immediately and flash if a misfire is severe enough to cause catalyst damage. |
| • | The torque converter clutch (TCC) will disable whenever a misfire is being detected with or without a misfire DTC set--automatic transmission only. |
| • | The PCM will record the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information. |
| • | A history DTC is stored. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault within the Freeze Frame conditions that the DTC failed. |
| • | A history DTC will clear after 40 consecutive warm up cycles without a fault. |
| • | A scan tool can clear the DTCs. |
Diagnostic Aids
An intermittent DTC can also be the result of a defective reluctor wheel. Remove the crankshaft sensor and inspect the reluctor wheel through the crankshaft sensor mount hole. Check the porosity and the condition of the reluctor wheel.
Whenever the DTC is an intermittent, refer to the Driveability Symptom Tables.
Perform the fuel Injector Balance Test. Refer to Fuel Injector Balance Test .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The misfire is considered random on all cylinders if, while viewing the misfire counters in the misfire data list, the misfire seems to move to different cylinders.
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The misfire is considered consistent if the misfire is occurring on the same cylinders consistently.
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When checking the spark at the spark plug wires, the spark should be consistent. A few sparks then nothing, is no spark.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, record the Freeze Frame and the Failure records for reference with a scan tool. This data will be lost when you use the Clear DTC information function. Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 | Install the scan tool. Are there any other DTCs stored? | -- | Go to the applicable DTC table | |
3 |
Is the Misfire counter increasing? | -- | ||
4 |
Does the scan tool indicate a misfire is present? | -- | ||
Is the misfire random on all cylinders? | -- | |||
Is the misfire consistent on specific cylinders? | -- | -- | ||
Does the tester indicate spark is consistent on all tested ignition wires? | -- | |||
8 |
Did you find a problem? | -- | ||
9 |
Did the misfires change cylinders? | -- | ||
10 |
Did you find a problem? | -- | ||
11 | Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test . Did you find a problem? | -- | ||
12 |
Does the injector test lamp flash for each injector? | -- | Go to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) or Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F) | |
13 | Check the injector harness for a short to voltage between the PCM connector and the injector connector that failed the Balance Test using a DMM. Is the voltage above the specified value? | 0-1 V | ||
14 | Repair the short to voltage on the injector control circuit. Is the action complete? | -- | -- | |
15 | Replace the spark plugs. Refer to Spark Plug Replacement in Engine Electrical. Is the action complete? | -- | -- | |
16 | Physically and visually check for these conditions in the following order:
Repair as necessary. Did you find a problem? | -- | ||
17 |
Did you find a problem? | -- | Go to Diagnostic Aids | |
18 | Perform the CKP Variation Learn Procedure. Refer to Crankshaft Position System Variation Learn . Is the action complete? | -- | -- | |
19 |
Does the scan tool indicate that this diagnostic Ran and Passed? | -- | ||
20 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK |
