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 three-way catalytic converter (TWC). The malfunction indicator lamp (MIL) will flash if converter damage conditions are present.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0125, P0335, P0336, P0341, P0342, P0343, P0500, P0502, P0503, P1120, P1220, P1221, or P1258 are not set. |
| • | The engine speed is between 425-3000 RPM. |
| • | The ignition voltage is between 10-18 volts. |
| • | The engine coolant temperature (ECT) is between -7°C-130°C (+19°F-266°F). |
| • | The fuel level is more than 10 percent. |
| • | The throttle angle is steady within 1 percent. |
| • | The anti-lock break system (ABS) and the traction control 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 in a steady state. |
| • | The engine is not in fuel shut-off or in decel fuel cut-off. |
| • | The antilock brake system (ABS) signals are not exceeding the 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
Important:
• Before you service the PCM and the throttle actuator control (TAC),
remove any debris from the module connector surfaces. Inspect the module connector
gaskets when you diagnose or replace the modules. Ensure that the gaskets
are correctly installed. The gaskets prevent contaminate intrusion
into the modules. • For any test that requires probing the PCM or probing
a component harness connector, use theJ 35616
connector test adapter kit . Using this kit prevents
damage to the harness and component terminals. Refer to
Using Connector Test Adapters
in Wiring Systems.
| • | Running the vehicle out of fuel causes sufficient misfire to set DTC P0300. A vehicle that is out of fuel may have DTC P0461 and DTC P1431 also set. |
| • | A restricted fuel filter can cause sufficient misfire to set DTC P0300. Refer to Fuel System Diagnosis . |
| • | A misfire that only occurs during certain conditions may be difficult to locate. Observe the Freeze Frame and the Failure Records in order to determine when the DTC set. |
| • | Excessive vibration from sources other than the engine could cause a misfire DTC. Possible sources of vibration are listed below: |
| - | Variable thickness in the brake rotor |
| - | An unbalanced propeller shaft |
| - | Certain rough road conditions |
| • | If more than 1 cylinder is misfiring, the scan tool may only display 1 misfiring cylinder. This condition is not apparent until the repair is completed. Also, if an ignition coil or module ground circuit is open for 1 side of the engine, the scan tool may only display 2 or 3 misfiring cylinders. Inspect the ground circuit for the ignition coil and for the modules on the cylinder bank of the engine that has more than one misfiring cylinder. |
| • | A misfire may not be apparent at idle. The misfire may only occur above idle during a load. Road-test the vehicle, and monitor the misfire current counters. |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The Misfire Current Counters will not increment if certain DTCs set at the same time or after DTC P0300 sets.
If more than 1 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 of the injector fuses is open, only 2 or 3 Misfire Current Counters may increment for the corresponding side of the engine.
Wetting down the secondary ignition system with water from a spray bottle may help to locate damaged or deteriorated components. When you apply the water, look and listen for arcing or for misfiring.
If the Misfire Current Counters are incrementing and there is no apparent misfire, an erratic crankshaft position (CKP) sensor signal could be the cause. Perform the diagnostic that are listed on the table for DTC P0335 first if you suspect this condition.
If a misfire is present and you suspect a fuel control concern, 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 a small amount.
-
If the engine misfire moves with the spark plug, this is good indication that you should replace the spark plug.
-
An engine mechanical condition can cause a spark plug to gas foul. Inspect for loose rockers, for collapsed lifters, or for worn camshaft lobes.
-
If 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 Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||||||||||
|
Important: If any DTCs other than P0135 and P0155 are set, refer to those DTCs before proceeding with this diagnostic.
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 for the following conditions:
Did any of the above inspections 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 | |||||||||||||||||||||
8 |
Is the ignition wire resistance less than the specified resistance? | 700 ohms | Go to Step 16 | |||||||||||||||||||||
9 |
Does the spark plug appear 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.
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 without Internal Engine Noises in Engine Mechanical | Go to Step 12 | ||||||||||||||||||||
|
Important: If the Fuel System Diagnosis does not isolate the condition, refer to Base Engine Misfire without Internal Engine Noises in Engine Mechanical. 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. 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. If you find an improper gap, use a wire-type gauge in order to re-gap spark plugs. Refer to Spark Plug Replacement . 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 | -- | ||||||||||||||||||||
Was the MIL 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 |
