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 Setting the DTC
| • | The misfire total is greater than 12 counts. |
| • | The engine speed is between 469 RPM and 6406 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 15 seconds. |
| • | The Throttle Position (TP) hasn't changed more than 8% in 1 second. |
| • | DTCs P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0401, P0404, P0405, P0502, P0503, P0601, P0742, P1133, and P1404 not set. |
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.
Test Description
Number(s) below refer to the step number(s) 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. |
| • | For air leaks at the throttle body mounting area and intake manifold sealing surfaces. |
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This step determines if DTC P0304 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 misfire is present. A history misfire counter will store the number of the 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 light J 34780-2 to test the harness wiring and for PCM control of the injectors.
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Perform the Injector Coil Test Procedure 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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Before replacing the PCM, check the terminals for improper mating, broken locks, or physical damage to the wiring harness. Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be performed. Refer to the latest Techline information for PCM reprogramming and also refer to the Powertrain Control Module (PCM) for the Crankshaft Position System Variation Procedure.
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Replace any spark plugs that are worn, cracked or fouled. Refer to the 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 cylinder #4 is possible at this point (i.e. valve train, compression, etc.). Refer to the Engine Mechanical portion of the service manual.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
Refer to Test Description for additional information. Are any component DTCs set? | -- | Go to DTC Table first | ||
Were any repairs necessary? | -- | |||
Is the Misfire Current #4 counter incrementing? | -- | |||
5 |
Does the spark tester spark? | -- | ||
Is the Misfire Current #4 counter incrementing? | -- | |||
7 | Was a repair made from the visual/physical inspection? | -- | Go to Diagnostic Aids | |
8 |
Is the Misfire Current #4 counter incrementing? | -- | ||
9 |
Is the spark plug cable resistance less than the specified value? | 30000 ohms | ||
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 injector test light blink? | -- | |||
Perform the Injector Coil Test Procedure , refer to Fuel Injector Solenoid Coil Test . Is cylinder #4 injector OK? | -- | |||
15 |
Did the test light illuminate? | -- | ||
Did the test light remain OFF? | -- | |||
17 | Connect the test light to B+ and again probe the fuel injector control circuit terminal. Did the test light remain OFF? | -- | ||
18 | Inspect the injector control electrical connector and the PCM electrical connector and connections for an open circuit. Are the connections OK? | -- | ||
19 | Repair the short to ground in cylinder #4 fuel injector control circuit. Is the action complete? | -- | -- | |
Replace the PCM. Is the action complete? | -- | -- | ||
21 | Repair the connector or connections. Is the action complete? | -- | -- | |
Replace the malfunctioning spark plug. Is the action complete? | -- | -- | ||
23 | Replace the spark plug cable. Is the action complete? | -- | -- | |
24 | Replace the cylinder #1 and #4 ignition coil. Is the action complete? | -- | -- | |
25 | Replace the ICM. Is the action complete? | -- | -- | |
26 | Repair the short to voltage in cylinder #4 fuel injector control circuit. Is the action complete? | -- | -- | |
Repair the open ignition feed circuit between the fuel injector harness electrical connector and the fuel injector connector. Is the action complete? | -- | -- | ||
Check for a basic engine problem, refer to the Engine Mechanical portion of the service manual. Is the action complete? | -- | -- | ||
29 | Replace the malfunctioning fuel injector. 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 applicable DTC Table | System OK |
