System Description
The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensors and from the camshaft position (CMP) sensor in order to determine if engine misfire is occurring. By monitoring the variations in the crankshaft rotational speed for each cylinder, the PCM is able to detect individual cylinder misfire events. A misfire rate that is high enough can cause damage to the 3-way catalytic converter. The malfunction indicator lamp (MIL) will flash if converter-damaging conditions are present.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0335, P0336, P0341, P0342, P0343, P0500, P0502, P0503, and P1258 are not set. |
| • | The engine speed is between 450-3,001 RPM. |
| • | The ignition voltage is between 10-18 volts. |
| • | The engine coolant temperature is between -7°C (19°F)-130°C (266°F). |
| • | The fuel level is more than 10 percent. |
| • | The throttle position (TP) sensor angle is steady within 1 percent. |
| • | The anti-lock brake system (ABS) system and the traction control system are not active. |
| • | The transmission is not changing gears. |
| • | The secondary air injection (AIR) diagnostic test is not in progress. |
| • | The A/C clutch is not changing states. |
| • | The PCM is not in fuel shut-off mode or decel fuel cut-off mode. |
| • | The ABS signals not exceeding the rough road thresholds. |
Conditions for Setting the DTC
| • | The PCM determines that an emissions-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
Important:
• Remove any debris from the PCM connector surfaces before servicing
the PCM. Inspect the PCM connector gaskets when you diagnose or replace the
PCM. Ensure that the gaskets are installed correctly. The gaskets
prevent contaminant intrusion into the PCM. • For any test that requires probing the PCM or component
harness connectors, use the J 35616
connector test adapter kit . Using this kit prevents
any damage to the harness connector terminals. Refer to
Using Connector Test Adapters
in Wiring Systems.
The following conditions may cause a misfire:
| • | Running the vehicle out of fuel causes sufficient misfire to set DTC P0300. A vehicle that is out of fuel may have DTC P0461 also set. |
| • | A restricted fuel filter can cause sufficient misfire to set DTC P0300. Refer to Fuel System Diagnosis . |
| • | 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 mis-firing, the scan tool may only display one cylinder mis-firing. This condition will not be apparent until you complete the repair. Also, if an ignition coil or module ground circuit is open for one side of the engine, the scan tool may only display 2 or 3 cylinders mis-firing. Inspect the ground circuit for the ignition coil or modules on the cylinder bank of the engine that has more than one cylinder mis-firing. |
| • | Excessive vibration from sources other than the engine could cause a misfire DTC. The following conditions are possible sources of vibration: |
| - | A variable thickness brake rotor |
| - | A drive shaft that is not balanced |
| - | Certain rough road conditions |
For an intermittent condition, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
A misfire may not be apparent at idle. The misfire may only occur above idle or under a load. Road-test the vehicle, and monitor the Misfire Current Counters.
If certain DTCs set at the same time or after DTC P0300 sets, the Misfire Current Counters will not increment . Refer to conditions for running DTC P0300 for the applicable DTC list.
If more than one cylinder is misfiring, the Misfire Current Counters may increment for only one cylinder. For example, cylinder 1 and cylinder 8 are both misfiring, but only Cylinder 8 increments on the Misfire Current Counter.
If one injector fuse is open, only 2 or 3 Misfire Current Counters may increment for the corresponding side of the engine.
Wetting the secondary ignition system with water from a spray bottle may help to locate the damaged or deteriorated components. When you apply the water, look and listen for arcing or misfiring.
If the Misfire Current Counters are incrementing and there is no apparent misfire, an erratic CKP sensor signal could be the cause. If you suspect that this condition exists, perform the diagnostic test for DTC P0335 first.
If a misfire is present and you suspect a fuel control condition, force the fuel system into Open Loop using the scan tool, and allow the engine to run for a few minutes. If this procedure eliminates the misfire, refer to any fuel control related DTCs which are set. If no other DTCs are set, refer to the Engine Scan Tool Data List.
-
The cylinder with the more significant misfire may cause another cylinder's counter to increment by only a small amount.
-
If the engine misfire moves with the spark plug, this is good indication that you should replace the spark plug.
-
If you cannot locate a fuel system condition, refer to Engine Mechanical - 5.7L. An engine mechanical condition can cause a spark plug to gas foul. Inspect for loose rockers, and inspect for collapsed lifters or for worn camshaft lobes.
-
If the customer's concern is that the MIL is 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:
Use the scan tool in order to monitor all the Misfire Current Counters on the misfire data list. There are 8 counters, with one counter per cylinder. 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 items:
Did any of the above tests isolate a condition requiring a repair? | -- | Go to Step 17 | Go to Step 6 | ||||||||||||||||||||||||||
6 |
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 Procedure does not isolate the condition, refer to Base Engine Misfire without Internal Engine Noises in Engine Mechanical-5.7L.
Did the misfire move with the spark plug? | -- | Go to Step 15 | ||||||||||||||||||||||||||||
11 | Are the spark plugs oil or coolant fouled? | -- | Go to Base Engine Misfire with Coolant Consumption or Base Engine Misfire with Excessive Oil Consumption in Engine Mechanical-5.7L | Go to Step 12 | ||||||||||||||||||||||||||
|
Important: If the Fuel System is OK, refer to Base Engine Misfire without Internal Engine Noises in Engine Mechanical-5.7L. Are the spark plugs gas-fouled? | -- | Go to Fuel System Diagnosis | Go to Step 13 | |||||||||||||||||||||||||||
13 |
Important: If the Injector Coil Test Procedure does not isolate the condition, refer to Base Engine Misfire without Internal Engine Noises in Engine Mechanical-5.7L. Do the spark plugs show any signs of being cracked, worn, or improperly gapped? | -- | Go to Step 14 | |||||||||||||||||||||||||||
14 |
Is the action complete? | -- | 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 | -- | ||||||||||||||||||||||||||
Was the customer's concern that the MIL was flashing? | -- | Go to DTC P0420 or P0430 | 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 |
