System Description
The Powertrain Control Module (PCM) monitors both the crankshaft and the camshaft position in order to detect an engine misfire. A rapid decrease in the crankshaft speed indicates misfire. The PCM may require that several consecutive misfire conditions are detected before storing this DTC and before illuminating the MIL. Under light misfire conditions, the PCM may require more than one trip to set this DTC. Under a severe misfire, the PCM flashes the MIL. A flashing MIL indicates that there is a misfire that is capable of damaging the catalytic converter. The torque converter clutch (TCC) disables momentarily in order 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 469-5900 RPM. |
| • | The battery voltage is between 9-17 volts. |
| • | The engine coolant temperature (ECT) is between -7°C and +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 throttle position (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) illuminates if the fault is active within the same conditions for two out of eighty ignition cycles and a misfire is present. |
| OR |
| The MIL illuminates after two consecutive ignition cycles during in which the diagnostic runs with the fault active |
| OR |
| The MIL illuminates immediately and flashes if a misfire is severe enough to cause any catalyst damage. |
| • | In vehicles with automatic transmission only, the torque converter clutch (TCC) is disabled when a misfire is present. |
| • | The PCM records the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers. |
| • | A history DTC is stored. |
| • | The coolant fan turns ON. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after three consecutive ignition cycles during which the diagnostic runs without a fault present under the Freeze Frame conditions that existed when the DTC failed. |
| • | A history DTC clears after 40 consecutive warm up cycles without a fault. |
| • | Clear the MIL/DTCs with a scan tool. |
Diagnostic Aids
An intermittent can also be the result of a defective reluctor wheel. Remove the crankshaft sensor and inspect the reluctor wheel through the sensor mount hole. Check for porosity and examine 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 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 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. |
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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 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.
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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 | Values | 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 applicable DTC | ||
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 |
Was a repair necessary? | -- | ||
|
Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement . Replace the PCM. 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 Control Module Replacement in Engine Electrical. Is the action complete? | -- | -- | |
25 | Replace the ICM. Refer to Ignition Control Module Replacement in Engine Electrical. 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 applicable DTC | System OK |
