Refer to
Ignition Controls
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 malfunction indicator lamp (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 (TCC) is disabled momentarily to determine if the misfire was due to a rough road condition (automatic transmission only).
Conditions for Running the DTC
| • | No active MAP DTCs |
| • | No active IAT DTCs |
| • | No active ECT DTCs |
| • | No active TP DTCs |
| • | No active oxygen sensor DTCs |
| • | No active fuel trim DTCs |
| • | No active CKP DTCs |
| • | No active KS DTCs |
| • | No active CMP DTCs |
| • | No active VSS DTCs |
| • | No active IAC DTCs |
| • | No active PCM memory DTCs |
| • | The engine speed is between 469 RPM and 5,906 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 fuel level is above 10 percent |
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. |
| • | Use a scan tool to 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 System Diagnosis .
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
Whenever a DTC P0108 is present, verify that no misfire is present by viewing the misfire counters. DTC P0108 may set as a result of a misfire.
-
A visual and physical inspection should include checking the following conditions:
| • | The wiring for proper connections, pinches, and cuts. |
| • | Clean and tight PCM grounds. |
| • | The vacuum hoses for splits, kinks and proper connections as shown on the vehicle emission information label. Check thoroughly for any type of leak or restriction. |
-
This step determines if the Misfire DTC is the result of a hard malfunction or an intermittent condition.
-
If the misfire is not present, operate the vehicle under the conditions found in the Freeze Frame Data in order to detect the misfire. Depending on the engine load, the conditions may have to be maintained for up to 20 seconds. If the misfire accumulators start to increment, the misfire is present. A history misfire counter will record the number of misfires that occur until the DTC is cleared. The current counter must count a total of at least 195 misfires before the history counter begins storing the misfire information.
-
No spark on one coil may be caused by an open secondary circuit. Therefore, the coils secondary resistance should be checked.
-
Use the injector test lamp to test the harness wiring and for PCM control of the injectors.
-
Perform the Fuel Inj Coil Test on the misfiring cylinder only.
-
Determines if the injector driver circuit is shorted to ground, voltage or if the PCM is malfunctioning.
-
The replacement PCMs must be programmed, and the Crankshaft Position System Variation Learn Procedure must be performed.
-
Replace any spark plugs that are worn, cracked, or fouled.
-
Since the voltage is supplied to the injector on a single circuit before the injector harness, the malfunction may only be a poor connection or an open in the injector harness. An open before the harness may result in a Cranks But Does Not Run complaint.
-
A basic engine problem that affects only a single cylinder is possible at this point (i.e. valve train, compression, etc.).
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Are any component DTCs set? | -- | |||
Were any repairs necessary? | -- | |||
With the engine idling, install a scan tool. Is the misfire current counter incrementing on the cylinder that had a misfire DTC? | -- | |||
5 |
Does the spark tester spark? | -- | ||
Is the misfire current counter incrementing on the cylinder that indicated a misfire? | -- | |||
7 | Was a repair made from the visual and physical inspection? | -- | Go to Diagnostic Aids | |
8 |
Is the misfire current counter incrementing on the cylinder that indicated a misfire? | -- | ||
9 |
Is the spark plug cable resistance less than the specified value? | 1,000 ohms/in | ||
Is the resistance within the specified range? | 5-8 K ohms | |||
11 |
Did spark occur on the spark tester? | -- | ||
12 |
Were any repairs necessary? | -- | ||
Does the fuel injector test lamp blink? | -- | |||
Perform the Injector Coil/Balance Test Procedure . Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) . Is the fuel injector OK for the cylinder that had indicated a misfire? | -- | |||
15 |
Did the test lamp illuminate? | -- | ||
Did the test lamp remain OFF? | -- | |||
17 |
Did the test lamp remain OFF? | -- | ||
18 | Inspect the fuel injector harness connector and the PCM harness connectors and connections for an open circuit. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Are the connections OK? | -- | ||
19 |
Did you find and correct the condition? | -- | ||
|
Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming Replace the PCM. Did you complete the replacement? | -- | -- | ||
21 | Repair the connector or connections. Refer to Connector Repairs in Wiring Systems. Is the action complete? | -- | -- | |
Replace the malfunctioning spark plug. Refer to Spark Plug Replacement in Engine Electrical. Did you complete the replacement? | -- | -- | ||
23 | Replace the spark plug cable. Refer to Spark Plug Wire Harness Replacement in Engine Electrical. Did you complete the replacement? | -- | -- | |
24 | Replace the defective ignition coil. Refer to Ignition Coil and Ignition Coil Module Replacement in Engine Electrical. Did you complete the replacement? | -- | -- | |
25 | Replace the ICM. Refer to Ignition Coil and Ignition Coil Module Replacement in Engine Electrical. Did you complete the repair? | -- | -- | |
26 |
Did you complete the repair? | -- | ||
Repair the open ignition positive voltage circuit for the fuel injector. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | ||
Check for a basic engine problem, refer to Base Engine Misfire Diagnosis in Engine Mechanical. Did you complete the repair? | -- | -- | ||
29 | Replace the malfunctioning fuel injector. Refer to Fuel Injector Replacement . Did you complete the repair? | -- | -- | |
30 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
31 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | System OK |
