System Description
The powertrain control module (PCM) uses information from the ignition control (IC) module and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring the variations in the crankshaft rotation speed for each cylinder the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic (TWC) converter to overheat under certain conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for the TWC converter overheating are present.
Conditions for Running the DTC
| • | DTCs P0105, P0107, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0137, P0138, P0140, P0171, P0172, P0325, P0336, P0502, P0503, P0506, P0507, P0601, P0602, P1133, P1137, P1138, P1171, 1336, or P1621 are not set. |
| • | The engine speed is between 469-5900 RPM. |
| • | The battery voltage is between 9-17 volts. |
| • | The engine coolant temperature (ECT) is between -7 to +123°C (20-254°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 PCM is detecting a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed the mandated standard.
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
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. Inspect the porosity and the condition of the reluctor wheel.
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/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 Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 | Install the scan tool. Are there any other DTCs stored? | -- | Go to Step 3 | |
3 |
Is the Misfire counter increasing? | -- | Go to Step 5 | Go to Step 4 |
4 |
Does the scan tool indicate a misfire is present? | -- | Go to Step 5 | Go to Step 15 |
Is the misfire random on all cylinders? | -- | Go to Step 10 | Go to Step 6 | |
Is the misfire consistent on specific cylinders? | -- | Go to Step 7 | -- | |
Does the tester indicate spark is consistent on all tested spark plug wires? | -- | Go to Step 8 | Go to Step 9 | |
8 |
Did you find a problem? | -- | Go to Step 14 | Go to Step 9 |
9 |
Did the misfires change cylinders? | -- | Go to Step 12 | Go to Step 11 |
10 |
Did you find a problem? | -- | Go to Step 15 | Go to Step 13 |
11 | Perform the Fuel Injector Balance Test. Did you find a problem? | -- | Go to Step 16 | Go to Step 14 |
12 | Replace the spark plugs. Is the action complete? | -- | Go to Step 16 | -- |
13 | Physically and visually check for these conditions in the following order:
Repair as necessary. Did you find a problem? | -- | Go to Step 16 | Go to Step 14 |
14 |
Did you find a problem? | -- | Go to Step 16 | Go to Diagnostic Aids |
15 | Perform the crankshaft position (CKP) variation learn procedure. Refer to Crankshaft Position System Variation Learn . Is the action complete? | -- | Go to Step 16 | -- |
16 |
Does the DTC run and pass? | -- | Go to Step 17 | Go to Step 2 |
17 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK |
