System Description
The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic converter (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0128, P0335, P0336, P0341, P0342, P0343, P0500, P0502, P1114, P1115, P1120, P1220, P1258, or P1336 are not set. |
| • | The engine speed is between 450-5,000 RPM. |
| • | The ignition voltage is between 10-18 volts. |
| • | The engine coolant temperature (ECT) is between -7 to +130°C (19-266°F). |
| • | The fuel level is more than 10 percent. |
| • | The throttle position (TP) sensor angle is steady within 1 percent. |
| • | The antilock brake system (ABS) and traction control systems are not active. |
| • | The transmission is not changing gears. |
| • | The A/C clutch is not changing states. |
| • | The PCM is not in fuel shut-off or decel fuel cut-off mode. |
| • | The ABS signal is not exceeding rough road thresholds. |
Conditions for Setting the DTC
| • | The PCM determines that an emission type misfire is present. |
| • | The PCM determines that a catalyst damaging misfire is present. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
| • | Running the vehicle out of fuel causes sufficient misfire to set DTC P0300. A vehicle that is out of fuel may have fuel level DTCs also set. |
| • | Water contamination in the fuel system can cause a single cylinder to misfire as well as cause a random misfire. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| • | A restricted fuel filter can cause sufficient misfire to set DTC P0300. Refer to Fuel System Diagnosis . |
| • | Excessive vibration from sources other than the engine could cause a misfire DTC. The following are possible sources of vibration: |
| - | Variable thickness brake rotor |
| - | Drive shaft not balanced |
| - | Certain rough road conditions |
| • | Observe if more than one cylinder is misfiring, the scan tool may only display one cylinder misfiring. This will not be apparent until the repair is completed. If an ignition coil ground circuit is open for one side of the engine, the scan tool may only display 2 or 3 cylinders misfiring. Inspect the ground circuit for the ignition coil on the cylinder bank of the engine that has more then one cylinder misfiring. |
| • | Perform the following procedures to diagnosis conditions that may be causing the misfire counter to increment: |
| - | Wetting down the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply the water. |
| - | If the Misfire Current counters are incrementing and there is no apparent misfire, an erratic CKP sensor signal could be the cause. Perform the diagnostic table for DTC P0335 first if this condition is suspected. |
| - | If a misfire is present and you suspect a fuel control problem, force the fuel system into Open Loop using the scan tool and allow the engine to run for a few minutes. If this eliminates the misfire, refer to any fuel control related DTCs which are set. If no other DTCs are set, refer to Scan Tool Data List . |
| - | A misfire may not be apparent at idle. The misfire may only occur above idle under a load. Road test the vehicle and monitor the misfire current counters. |
| - | If more than one cylinder is misfiring, the misfire current counters may only increment for one cylinder. Example: Cylinders 1 and 8 are both misfiring, yet only cylinder 8 increments on the misfire current counter. |
| - | If one of the injector fuses is open, only 2 or 3 misfire current counters may increment for the corresponding side of the engine. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step diagnoses the conditions that are causing the misfire counter to increment.
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The cylinder with the more significant misfire may cause another cylinder counter to increment only by a small amount.
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If the engine misfire moves with the spark plug, this is good indication that you should replace the spark plug.
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An engine mechanical problem can cause a spark plug to gas foul. Inspect for loose rockers, collapsed lifters, or worn camshaft lobes.
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If the customer concern is the MIL flashing, this indicates that a Catalyst Misfire has occurred. Drive the vehicle in the conditions to run the catalyst diagnostic.
Step | Action | Values | Yes | No | ||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||||||||||||
|
Important:
Are any of the Misfire Current counters incrementing? | -- | Go to Step 4 | Go to Step 3 | |||||||||||||||||||||||
3 |
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||||||||||||||||
Is only one misfire counter incrementing? | -- | Go to Step 6 | Go to Step 5 | |||||||||||||||||||||||
5 | Inspect the following components:
Did any of the above tests isolate a condition requiring a repair? | -- | Go to Step 17 | Go to Step 6 | ||||||||||||||||||||||
6 |
Important: Before disconnecting the injector harness, refer to Fuel Injection Fuel Rail Assembly Replacement . There is a special procedure for disconnecting the fuel injector harness connectors. Is the Injector Test Lamp flashing? | -- | Go to Step 7 | Go to DTC P0200 | ||||||||||||||||||||||
7 |
Does the spark jump the tester gap and is the spark consistent? | -- | Go to Step 9 | Go to Step 8 | ||||||||||||||||||||||
8 |
Is the ignition wire resistance less than the specified resistance? | 700 ohms | Go to Step 16 | |||||||||||||||||||||||
9 |
Does the spark plug appear to be OK? | -- | Go to Step 10 | Go to Step 11 | ||||||||||||||||||||||
Important: If the injector coil test appears to be OK, refer to the appropriate base engine misfire diagnostic procedures. Did the misfire move with the spark plug? | -- | Go to Step 15 | ||||||||||||||||||||||||
11 | Are the spark plugs oil or coolant fouled? | -- | Go to Step 12 | |||||||||||||||||||||||
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Important: If the fuel system appears to be OK, refer to the appropriate base engine misfire diagnostic procedures. Are the spark plugs gas fouled? | -- | Go to Fuel System Diagnosis | Go to Step 13 | |||||||||||||||||||||||
13 |
Important: If the injector coil test appears to be OK, refer to appropriate base engine misfire diagnostic procedures. Do the spark plugs show any signs of being cracked, worn, or improperly gapped? | -- | Go to Step 14 | |||||||||||||||||||||||
14 | Replace or re-gap spark plugs. Refer to Spark Plug Replacement . If an improper gap is found, be sure to re-gap spark plugs using a wire type gage. Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||||||||||||
15 | Replace the faulty spark plugs. Refer to Spark Plug Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||||||||||||
16 | Replace the faulty ignition wires. Refer to Spark Plug Wire Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||||||||||||
If the customers concern that the MIL was flashing, were DTC P0420 or DTC P0430 set? | -- | Go to Step 18 | ||||||||||||||||||||||||
18 |
Does the DTC run and pass? | -- | Go to Step 19 | Go to Step 2 | ||||||||||||||||||||||
19 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK |
