Refer to
Ignition Controls
for wiring view.
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 Setting the DTC
| • | Misfire total is greater than 12 counts. |
| • | Engine speed is between 469 RPM (automatic trans.) or 750 RPM (manual trans.) and 3400 RPM |
| • | Battery voltage is between 9 volts and 17 volts. |
| • | Engine Coolant Temperature (ECT) is between -7° C (20° F) and 123° C (254° F). |
| • | Engine has been running more than 15 seconds. |
| • | Throttle Position (TP) hasn't changed more than 8 % in 1 second. |
| • | DTC(s) P0106, P0107, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0401, P0502, P0503, P0601, P0742, P1133, and P1406 not set. |
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 disablesd 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 crankshaft sensor and inspect reluctor wheel through sensor mount hole. Check for porosity and condition of the reluctor wheel.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
-
The Powertrain OBD System Check prompts the Technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. This information on the scan tool can be referred to later.
-
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/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. |
-
This step determines if DTC P0304 is the result of a hard failure 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 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 secondary resistance of the coil should be checked.
-
Use injector test light J 34780-2 to test the harness wiring and for PCM control of the injectors.
-
Perform the Injector Coil Test Procedure on the misfiring cylinder only.
-
Determines if the injector driver circuit is shorted to ground or voltage or if the PCM is faulty.
-
Before replacing the PCM, check terminals for improper mating, broken locks, or physical damage to the wiring harness. Replacement PCMs must be reprogrammed. Refer to the latest Techline information for programming procedures.
-
Replace any spark plugs that are worn, cracked or fouled. Refer to Section 6A if any plugs are fouled or damaged due to an engine mechanical failure.
-
Since the voltage is supplied to the injector on a single circuit before the injector harness, the malfunctioning could only be caused from a poor connection or open in the injector harness. An open before the harness would result in a Cranks But Will Not Run complaint.
-
A basic engine problem that affects only cylinder #4 is possible at this point (i.e. valve train, compression, etc.). Refer to Section 6A.
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? | -- | |||
With engine running, Install a scan tool. 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? | 5-8k 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 driver circuit terminal. Did the test light remain OFF? | -- | ||
18 | Inspect the PCM connector and connections. Are the connections OK? | -- | ||
19 | Repair the short to ground in cylinder #4 fuel injector driver 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 cylinders #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 driver circuit. Is the action complete? | -- | -- | |
Repair the open ignition feed circuit between the fuel injector harness connector and the fuel injector connector. Is the action complete? | -- | -- | ||
Check for a basic engine problem, refer to Section 6A. Is the action complete? | -- | -- | ||
29 | Replace the faulty 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 |
