Circuit Description
The powertrain control module (PCM) monitors crankshaft and camshaft position to detect if the engine is misfiring. The PCM looks for a quick drop in crankshaft speed. This test is executed in blocks of 100 camshaft revolution tests. It may take between one to several test to store a DTC and illuminate the malfunction indicator lamp (MIL). Under light misfire conditions, it may also take more than one trip to set a DTC. Severe misfire will flash the MIL indicating that catalyst damage is possible.
Conditions for Setting the DTC
| • | Misfire total is greater than 1.75 percent. |
| • | Engine speed is between 469 RPM and 6500 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) has not changed more than 8 percent. |
| • | DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0133, P0134, P0171, P0172, P0200, P0300-P0304, P0325, P0335, P0341, P0342, P0441, P0502, P0503, P0506, P0507, P0562, P0563, P0601, P0742, P1133, P1171, and P1441 not set. |
Action Taken when the DTC Sets
Malfunction indicator lamp (MIL) illuminates after two consecutive driving cycles with the fault active if misfire is light. MIL will illuminate immediately if misfire is more severe and flash if misfire is severe enough to cause catalyst damage. Torque converter clutch (TCC) is disabled.
Conditions for Clearing the DTC
| • | The MIL will turn OFF after passing three consecutive diagnostic tests. |
| • | A history DTC will clear after 40 consecutive ignition cycles have occurred without a fault. |
| • | History and current DTCs can be cleared by using 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 wheel. Refer to Section 6A.
Verify electronic ignition control module (ICM) 11 pin harness connector terminal K, CKT 750 resistance is less than 0.5 ohms.
If DTC P0301 is intermittent, refer to Symptoms, Section 6E3-B.
Test Description
The numbers below refer to the step numbers on the diagnostic chart.
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If a DTC P0108 is present, verify no misfire is present by viewing the misfire counters. DTC P0108 may set as a result of misfire.
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A visual/physical inspection should include checking:
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This step determines if DTC P0304 is the result of a hard failure or an intermittent condition.
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If a plug boot is burned, the other plug on that ignition coil may still fire at idle. This step tests the system ability to produce at least 25,000 volts at each spark plug.
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If the misfire is not present it may be necessary to duplicate the conditions 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. If the misfire accumulators starts 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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Spark is available at the misfiring cylinder. At this point the misfire is being caused by a spark plug, a fuel injection problem or a basic engine problem. View Freeze Frame information to determine when the misfire was present when the DTC set.
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Replace any spare plugs that are worn, cracked or fouled. Refer to Section 6A if any plugs are fouled or damaged due to an engine mechanical failure.
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No spark, on one coil, may be caused by an open secondary circuit. Therefore, the coil's secondary resistance should be checked. Resistance readings above 20,000 ohms, but not infinite, will probably not cause a no start but may cause an engine miss under certain conditions.
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If no spark condition is cause by coil connections, a coil or a secondary boot assembly, the test light will blink. If the light blink. If the light does not blink, the fault is module connections or the module.
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Refer to Section 6E3-C4 for On Vehicle Service of the ignition system.
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Refer to Section 6E3-C4 for On Vehicle Service of the ignition system.
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Refer to Section 6E3-C4 for On Vehicle Service of the ignition system.
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Use injector test light J 34780-2 to test the harness wiring and for PCM control of the injectors.
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It is necessary to perform the Injector/Coil Balance Test Procedure on the misfiring cylinder only.
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Check for voltage from CKT 120.
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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 Section 6A.
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Determines if the injector driver circuit is shorted to ground or voltage or if the PCM is faulty.
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Since voltage is supplied to the injector on a single circuit before the injector harness, the fault could only be a poor connection or open in the injector harness. An open before the harness would result in a Crank But Won't Run complaint.
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Any circuitry, that is suspected as causing the complaint, should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wiring connections or physical damage to the wiring harness.
| • | Wiring for proper connections, pinches and cuts. |
| • | PCM grounds for being clean and tight. |
| • | Vacuum hoses for splits, kinks and proper connections as shown on the Vehicle Emission Information label. Check thoroughly for any type of leaks or restriction. |
| • | For air leaks at the throttle body mounting area and intake manifold sealing surfaces. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Was the On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | |
Refer to the Test Description for additional information. Are any component DTCs set? | -- | Go to DTC charts first | Go to Step 3 | |
Were any repairs necessary? | -- | Go to Step 6 | Go to Step 4 | |
Is the Misfire Current #4 counter incrementing? | -- | Go to Step 5 | Go to Step 6 | |
Does the spark tester spark? | -- | Go to Step 8 | Go to Step 10 | |
Road test the vehicle under various vehicle speeds, engine RPMs and engine loads while viewing the scan tool's current misfire counter screen for the related cylinder. Do any of the current misfire counters increment? | -- | Go to Step 5 | Go to Step 7 | |
7 | Was a repair made from the visual/physical inspection? | -- | Go to Diagnostic Aids | |
Is the Misfire Current #4 counter incrementing? | -- | Go to Step 18 | Go to Step 9 | |
Replace faulty spark plug. Is action complete? | -- | -- | ||
Is resistance less than the specified value? | 10K ohms | Go to Step 11 | Go to Step 12 | |
Does the test light blink? | -- | Go to Step 13 | Go to Step 14 | |
12 | Remove the ignition coil from the ignition coil housing and recheck the resistance between the secondary terminals of the ignition coil. Is resistance less than the specified values? | 10K ohms | Go to Step 15 | Go to Step 16 |
13 | Repair open or shorted ignition coil harness, boot ignition coil connection or replace ignition coil, ignition coil housing or boot assembly. Is action complete? | -- | -- | |
14 |
Were any repairs necessary? | -- | Go to Step 17 | |
Replace ignition coil springs for cylinders #1 and #4 coil. Is action complete? | -- | -- | ||
Replace cylinders #1 and #4 ignition coil. Is action complete? | -- | -- | ||
Replace the ICM. Is action complete? | -- | -- | ||
Does the injector test light blink? | -- | Go to Step 19 | Go to Step 20 | |
Perform the Injector Coil/Balance Test Procedure. Refer to Chart C-2A. Is the cylinder #4 injector OK? | -- | Go to Step 21 | Go to Step 22 | |
Did the test light illuminate? | -- | Go to Step 23 | Go to Step 24 | |
Check for a basic engine problem. Refer to Section 6A. Is action complete? | -- | -- | ||
22 | Replace faulty injector. Is action complete? | -- | -- | |
Did the test light remain OFF? | -- | Go to Step 25 | Go to Step 26 | |
Repair open ignition feed circuit between injector harness connector and injector connector. Is action complete? | -- | -- | ||
25 | Connect the test light to B+ and again probe the injector driver circuit terminal. Did the test light remain OFF? | -- | Go to Step 27 | Go to Step 28 |
26 | Repair short to voltage in cylinder #4 injector driver circuit. Is action complete? | -- | -- | |
27 | Inspect the PCM connector and connections. Are the connections OK? | -- | Go to Step 29 | Go to Step 30 |
28 | Repair short to ground in the cylinder #4 injector. Is action complete? | -- | -- | |
29 | Replace PCM. Is action complete? | -- | -- | |
Replace connector or connections. Is action complete? | -- | -- | ||
