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 tests 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 P0300 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 P0300 is the result of a hard failure or an intermittent condition.
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If all the accumulators are relatively equal, then the misfire is being caused by something that affects the entire engine. If they are not, then the misfire is being caused by something that is specific to two or more cylinders.
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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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Check fuel for water, alcohol, etc.
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A basic engine problem that effects all cylinders is the only possibility at this point. (i.e. cam timing, throttle body leak, restricted air flow, etc.) Refer to Section 6A.
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After repairs, verify no misfire by duplicating the conditions within Freeze Frame Data while watching the misfire counters.
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Tests the harness wiring and for PCM control of the injectors using injector test light J 34780-2.
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Check for voltage at the ignition feed circuit.
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This step check for ignition control (IC) frequency output from the PCM. Refer to PCM Terminal End View in front of this section for breakout box pin locations.
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If the driver circuit is shorted to ground, the light will be ON steady. If the driver circuit is shorted to voltage or open, the light will be OFF.
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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 Cranks But Will Not Run complaint.
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If the resistance is high, then the IC circuit is high.
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Determines if the circuit is shorted to ground
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Checks to see if voltage is present on IC circuits 1 or 2. If they are OK, PCM connections or PCM is faulty.
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Determine if the short to ground is in the IC circuits or the ICM.
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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.
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If a plug boot is burned, the other plug on that ignition coil may still fire at idle. This step test the system's ability to produce at least 25,000 volts at each spark plug.
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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.
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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 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.
| • | 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 4 | ||
Are any Misfire Current counters incrementing? | -- | Go to Step 5 | Go to Step 6 | |
Are all counters equal (within a percentage of each other)? | -- | Go to Step 7 | Go to Step 11 | |
Road test the vehicle under various vehicle speeds, engine RPMs and engine loads while viewing the scan tool's current misfire counters screen for cylinders #1, #2, #3, and #4. Do any of the current misfire counters increment? | -- | Go to Step 5 | Go to Diagnostic Aids | |
7 |
Is the fuel pressure within the specified value? | 284-325 kPa (41-47 psi) | Go to Step 8 | Go to Chart A-7 |
Check fuel for contamination. Is the fuel OK (uncontaminated)? | -- | Go to Step 9 | Go to Step 10 | |
Check for basic engine problem. Refer to Section 6A. Is action complete? | -- | -- | ||
Replace contaminated fuel. Is action complete? | -- | -- | ||
Does the injector test light blink? | -- | Go to Step 12 | Go to Step 13 | |
12 | Perform the Injector Coil/Balance Test Procedure. Refer to Chart C-2A. Are the injectors OK? | -- | Go to Step 14 | Go to Step 15 |
Did the test light illuminate? | -- | Go to Step 16 | Go to Step 18 | |
Are the frequency readings within the specified values? | 1-10 Hz | Go to Step 20 | Go to Step 22 | |
15 | Replace any faulty injectors. Is action complete? | -- | -- | |
Check the affected injector driver circuits for an open or short to ground or voltage. Was a problem found? | -- | Go to Step 17 | Go to Step 19 | |
17 | Repair open or shorted injector driver circuits. Is action complete? | -- | -- | |
Repair open ignition feed circuit between injector harness connector and injector connector. Is action complete? | -- | -- | ||
19 | Replace PCM. Is action complete? | -- | -- | |
Is the resistance between the specified values? | 0.6-2.6K ohms | Go to Step 30 | Go to Step 21 | |
21 | Repair open ignition control circuit. Is action complete? | -- | -- | |
Is the resistance more than the specified values? | 5K ohms | Go to Step 23 | Go to Step 24 | |
Is voltage within the specified value? | 0 V | Go to Step 25 | Go to Step 26 | |
Is the resistance infinite? | -- | Go to Step 27 | Go to Step 28 | |
25 | Inspect the PCM connector and connections. Are the connections OK? | -- | Go to Step 19 | Go to Step 29 |
26 | Repair short to voltage in the affected ignition control circuit. Is action complete? | -- | -- | |
27 | Replace the ICM. Is action complete? | -- | -- | |
28 | Repair short to ground in the affected ignition control circuit. Is action complete? | -- | -- | |
Repair connector or connections. Is action complete? | -- | -- | ||
Does spark tester spark? | -- | Go to Step 31 | Go to Step 32 | |
Replace any faulty spark plugs. Is action complete? | -- | -- | ||
Is resistance less than the specified value? | 10K ohms | Go to Step 33 | Go to Step 34 | |
Does the test light blink? | -- | Go to Step 35 | Go to Step 36 | |
34 | Remove the ignition coil from the ignition coil housing and recheck the resistance between the secondary terminals of the ignition coils. Is the resistance less than the specified value? | 10K ohms | Go to Step 37 | Go to Step 38 |
35 | Remove the ignition coil from the ignition coil harness, poor ignition coil connection or replace ignition coil, ignition coil housing or boot assembly. Is action complete? | -- | -- | |
36 | Visually inspect the ICM 11 harness connector to see if the connections are clean and tight and repair if necessary. Were any repairs necessary? | -- | Go to Step 27 | |
Replace the ignition coil springs. Is action complete? | -- | -- | ||
Replace faulty ignition coil. Is action complete? | -- | -- | ||
