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
| • | No active MAP DTC's |
| • | No active IAT DTC's |
| • | No active ECT DTC's |
| • | No active TP DTC's |
| • | No active Oxygen Sensor DTC's |
| • | No active Fuel Trim DTC's |
| • | No active KS DTC's |
| • | No active CKP DTC's |
| • | No active CMP DTC's |
| • | No active VSS DTC's |
| • | No active IAC DTC's |
| • | No active PCM Memory DTC's |
| • | The engine has been running more than 5 seconds. |
| • | The engine speed is between 469 RPM and 5906 RPM |
| • | The Engine Coolant Temperature (ECT) is between -7°C (20°F) and 123°C (254°F). |
| • | The battery voltage is between 9 volts and 17 volts. |
| • | The fuel level is more than 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. |
| • | 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 Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored in the scan tool for later reference.
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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.
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A visual/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. |
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This step determines if the Misfire DTC is the result of a hard malfunction or an intermittent condition
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When the misfire is not present, operate the vehicle to the conditions found in the Freeze Frame Data in order to detect misfire. Depending on the engine load, the conditions may have to be maintained for up to 20 seconds. Whenever the misfire accumulators start to increment, then the misfire is present. A history misfire counter will store the number of misfires that have occurred until the DTC is cleared. The current counter must count a total of at least 195 misfires before writing to the history counter.
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No spark on one coil may be caused by an open secondary circuit. Therefore, the coils secondary resistance should be checked.
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Use the injector test lamp to test the harness wiring and for PCM control of the injectors.
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Perform the Fuel Inj Coil Test on the misfiring cylinder only.
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Determines if the injector driver circuit is shorted to ground, voltage or if the PCM is malfunctioning.
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Replacement PCMs must be programmed and the crankshaft position system variation procedure must be performed. Refer to the latest Techline information for PCM programming.
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Replace any spark plugs that are worn, cracked or fouled. Refer to Engine Mechanical portion of the service manual if any plugs are fouled or damaged due to an engine mechanical failure.
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Since the voltage is supplied to the injector on a single circuit before the injector harness, the malfunction could only be a poor connection or an open in the injector harness. An open before the harness would result in a Cranks But Does Not Run complaint.
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A basic engine problem that affects only a single cylinder is possible at this point (i.e. valve train, compression, etc.).
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
Refer to the Test Description for additional information. Are any component DTCs set? | -- | Go to DTC Tables first | ||
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/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? | 1,000ohms/inch | ||
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. Are the connections OK? | -- | ||
19 |
Was a repair necessary? | -- | ||
Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
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. Is the action complete? | -- | -- | ||
23 | Replace the spark plug cable. Refer to Spark Plug Wire Harness Replacement in Engine Electrical. Is the action complete? | -- | -- | |
24 | Replace the defective ignition coil. Refer to Ignition Coil and Ignition Coil Module Replacement . Is the action complete? | -- | -- | |
25 | Replace the ICM. Refer to Ignition Coil and Ignition Coil Module Replacement . Is the action complete? | -- | -- | |
26 |
Was a repair necessary? | -- | ||
Repair the open ignition positive voltage circuit for the fuel injector. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | ||
Check for a basic engine problem, refer to Base Engine Misfire Diagnosis in Engine Mechanical. Is the action complete? | -- | -- | ||
29 | Replace the malfunctioning fuel injector. Refer to Fuel Injector Replacement . Is the action complete? | -- | -- | |
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? | -- | Go to the applicable DTC table | System OK |
