Circuit Description
The crankshaft position (CKP) sensor sends pulses to the engine control module (ECM) as the reluctor wheel teeth rotate past the sensor. Besides using these pulses in order to synchronize the ignition and fuel injector operation, the ECM also times the interval between each pulse and compares each new time interval with the previous one in order to determine when an excessive change in the crankshaft speed has occurred. A misfire causes an unexpected change in the crankshaft speed. A certain amount of acceleration and deceleration is expected between each firing stroke, but if the crankshaft speed changes are more than an expected amount, the ECM will interpret this as a misfire. The ECM continuously calculates the crankshaft position from the CKP sensor signals. This information is used in order to determine which cylinder is misfiring so that the ECM can increment the appropriate misfire counter and set the appropriate diagnostic trouble code (DTC), if necessary. DTCs P0301 through P0306 correspond to cylinders 1 through 6. If the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder will set. If the misfire is random and on multiple cylinders, DTC P0300 will set.
Conditions for Running the DTC
| • | DTCs P0100, P0115, P0116, P0335, P1120, or P1220 are not set. |
| • | The engine speed is between 520-6,520 RPM. |
| • | The torque management is not active. |
| • | The anti-lock brake/traction control (ABS/TC) system is not active. |
| • | Rough road is not detected. |
| • | The fuel cut-off is not active, including the traction control, the deceleration, the high speed/RPM . |
| • | The engine has been running for longer than 5 seconds. |
| • | The intake air temperature (IAT) is more than -8°C (+17°F). |
| • | The evaporative emission (EVAP) diagnosis is not active. |
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 ECM turns OFF the MIL after three consecutive drive trips that the diagnostic runs and does not fail within the same conditions that the DTC last failed. |
| • | A History DTC clears after forty consecutive warm-up cycles if no failures report by this diagnostic or any other emission related diagnostic. |
| • | The DTC can be cleared with a scan tool |
Diagnostic Aids
A misfire DTC could be caused by an excessive vibration from sources other than the engine. Check for the following possible sources:
| • | Tire or wheel out of round or balance |
| • | Variable thickness brake rotor or drum |
| • | Drive shaft not balanced |
| • | Certain rough road conditions |
| • | Damaged accessory drive belt |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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DTCs that may cause a misfire DTC to set may include those for injector control circuits, oxygen sensors, the EVAP system, or fuel trim.
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This test is to determine if there is a problem in the heated oxygen sensor (HO2S) or wiring that is causing the ECM to alter the fuel trim. When the sensors are disconnected, the fuel system should go into Open Loop. If the misfire counters stop incrementing, perform the HO2S diagnosis for banks 1 and 2, sensor 1.
Step | Action | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | |||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |||||||||
Check for other DTCs that may cause a misfire. Did you find any other DTCs? | Go to Step 3 | ||||||||||
3 |
Is the Misfire Current Counter incrementing? | Go to Step 4 | Go to Diagnostic Aids | ||||||||
4 | Visually/physically inspect the following items:
Did you find and correct the condition? | Go to Step 8 | Go to Step 5 | ||||||||
5 |
Did you find and correct the condition? | Go to Step 8 | Go to Step 6 | ||||||||
6 |
Did you find and correct the condition? | Go to Step 8 | Go to Step 7 | ||||||||
Is the Misfire Current Counter incrementing? | Go to Engine Compression Test in Engine Mechanical 3.0L (L81) | Go to DTC P0130 or P0150 | |||||||||
8 |
Does the DTC run and pass? | Go to Step 9 | Go to Step 2 | ||||||||
9 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | System OK | |||||||||
