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 misfire events.
• | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0117, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0315, P0335, P0336, P0341, P0342, P0343, P0502, P0503, P1114, P1115, P1121, P1122, and P1258 are not set. |
• | If the start-up engine coolant temperature (ECT) is less than -7°C (20°F), misfire detection is delayed until ECT is more than 21°C (70°F). If the start-up ECT is more than -7°C (20°F), misfire detection begins after a 5 second delay. |
• | The engine coolant temperature (ECT) is less than 130°C (266°F). |
• | The engine speed is between 425 and 5250 RPM. |
• | The system voltage is between 11 and 18 volts. |
• | The antilock brake system (ABS) and the traction control system are not active. |
• | The PCM is not in fuel shut-off, or decel fuel cut-off mode. |
• | The PCM is not receiving a rough road signal. |
• | The throttle position is steady within 15%. |
• | The A/C compressor clutch is steady. |
The powertrain control module (PCM) detects a deceleration in the crankshaft speed that is characteristic of either an emission type misfire or a catalyst-damaging type misfire.
• | 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. |
• | 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. |
The misfire index counts the number of misfires. The scan tool can monitor the misfire index. There is a current misfire counter and a history misfire counter for each cylinder. Use the current misfire counter in order to determine which cylinder is misfiring. Use the history misfire counter for misfires that are not currently present.
Many different conditions can cause an intermittent misfire. Inspect the following conditions:
• | Inspect the ignition control (IC) circuit for an intermittent short to ground. |
• | Ensure that the spark plug wires are securely attached to the spark plugs and the ignition coil. |
• | If the misfire occurs when the weather is damp, the condition could be due to worn spark plug wires. |
• | Test or inspect the fuel for the following conditions: |
- | Inspect for contaminated fuel. |
- | Inspect the fuel filter for a restriction. A restricted fuel filter can cause a misfire. |
• | Inspect for sticking intake or exhaust valves. |
• | Inspect the heated oxygen sensor (HO2S) for abnormal voltage readings. |
• | Inspect for a vacuum leak as a possible cause of the engine misfire. |
The numbers below refer to the step numbers on the diagnostic table.
This step determines if the engine is misfiring while operating on the gasoline fuel system.
If the Misfire Current Counters are incrementing, but the engine is NOT misfiring, this indicates a mechanical condition. For example, an accessory drive belt could cause this condition.
This step verifies that the Crankshaft Variation Learn Procedure is performed. A crankshaft variation that is not learned may cause the misfire counters to increment.
The spark should be consistent when you test the spark at the spark plug wires. The presence of few sparks then nothing indicates no spark.
A misfiring cylinder may cause more than one misfire counter to increment. Diagnose the fuel injector circuit of the cylinder that displays the highest level of misfire.
This step verifies that the catalytic convertors are operating correctly.
Step | Action | Values | Yes | No | ||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) | ||||||||||||||
2 |
Are there any other DTCs set? | -- | Go to Step 3 | |||||||||||||||
3 |
Are any of the Misfire Current Counters incrementing? | -- | Go to Step 7 | Go to Step 4 | ||||||||||||||
4 | Is the vehicle equipped with the Bi-Fuel option (KL6)? | -- | Go to Step 5 | Go to Step 6 | ||||||||||||||
Are any of the Misfire Current Counters incrementing? | -- | Go to DTC P0200 | Go to Step 6 | |||||||||||||||
6 |
Does the DTC fail this ignition cycle? | -- | Go to Step 7 | Go to Diagnostic Aids | ||||||||||||||
Is the engine misfiring? | -- | Go to Step 9 | Go to Step 8 | |||||||||||||||
Are any of the Misfire Current Counters incrementing? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical in the C/K Pickup Service Manual. | Go to Step 21 | |||||||||||||||
9 | Observe the Misfire Current Counters with a scan tool. Is there only one Misfire Current Counter incrementing? | -- | Go to Step 10 | Go to Step 16 | ||||||||||||||
Does the spark tester spark and is the spark consistent? | -- | Go to Step 12 | Go to Step 11 | |||||||||||||||
11 |
Is the resistance less than the specified value? | 625 ohms Per 30 cm (Per Foot) | Go to Electronic Ignition (EI) System Diagnosis in Engine Controls in the C/K Pickup Service Manual | Go to Step 18 | ||||||||||||||
12 |
Important: If the spark plug is gas, coolant, or oil fouled, determine the cause of the fouling. Refer to DTC P0172 or P0175 in Engine Controls in the C/K Pickup Service Manual for spark plugs that are gasoline fouled. Refer to Symptoms - Engine Mechanical in Engine Mechanical in the C/K Pickup Service Manual for spark plugs that are coolant or oil fouled. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 13 | ||||||||||||||
13 |
Did the misfire move with the spark plug? | -- | Go to Step 17 | Go to Step 14 | ||||||||||||||
Important:
Perform the Fuel Injector Coil Test. Refer to Fuel Injector Solenoid Coil Test . Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 15 | |||||||||||||||
15 | Perform the Fuel System Diagnosis. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 19 | Go to Symptoms - Engine Mechanical in Engine Mechanical in the C/K Pickup Service Manual. | ||||||||||||||
16 | Inspect or test for the following conditions:
Did you find and correct the condition? | -- | Go to Step 19 | Go to Symptoms - Engine Mechanical in Engine Mechanical in the C/K Pickup Service Manual. | ||||||||||||||
17 | Replace the spark plug. Refer to Spark Plug Replacement in Engine Controls in the C/K Pickup Service Manual. Did you complete the replacement? | -- | Go to Step 19 | -- | ||||||||||||||
18 | Replace the spark plug wire. Refer to Spark Plug Wire Replacement in Engine Controls in the C/K Pickup Service Manual. Did you complete the replacement? | -- | Go to Step 19 | -- | ||||||||||||||
19 | Was the customers concern that the was MIL flashing? | -- | Go to Step 20 | Go to Step 21 | ||||||||||||||
Does the DTC run and pass? | -- | Go to Step 21 | Go to DTC P0420 or P0430 in Engine Controls in the C/K Pickup Service Manual | |||||||||||||||
21 |
Does the DTC run and pass? | -- | Go to Step 22 | Go to Step 2 | ||||||||||||||
22 | With a scan tool, select Capture Info in order to observe the stored information. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK |