Circuit Description
Each cylinder is monitored individually for a misfire condition and can set a cylinder specific diagnostic trouble code (DTC). The powertrain control module (PCM) uses the crankshaft position (CKP) sensor and camshaft position (CMP) sensors to determine engine misfire. The CKP sensor and the CMP sensors monitor their respective components and evaluate changes in the crankshaft rotational speed for each cylinder. Irregular changes in the crankshaft rotational speed indicate a possible misfire. The malfunction indicator lamp (MIL) illuminates when the misfire rate equals or exceeds a pre-determined count. A misfire rate that is high enough can cause the catalytic converter to overheat under certain driving conditions. The MIL will flash ON and OFF when the conditions for catalytic converter overheating are present.
DTC Descriptors
This diagnostic procedure supports the following DTCs.
| • | DTC P0301 Cylinder 1 Misfire Detected |
| • | DTC P0302 Cylinder 2 Misfire Detected |
| • | DTC P0303 Cylinder 3 Misfire Detected |
| • | DTC P0304 Cylinder 4 Misfire Detected |
| • | DTC P0305 Cylinder 5 Misfire Detected |
| • | DTC P0306 Cylinder 6 Misfire Detected |
Conditions for Running the DTC
| • | DTC P0107, DTC P0108, DTC P0112, DTC P0113, DTC P0117, DTC P0118, DTC P0122, DTC P0123, DTC P0222, DTC P0223, DTC P0335, DTC P0336, DTC P1121, DTC P1122, DTC P1128, DTC P1129, DTC P2227, DTC P2228, and DTC P2229 are not set. |
| • | The engine speed is between 500-6,500 RPM. |
| • | The engine coolant temperature (ECT) is more than -10°C (14°F) at start-up. |
| • | The intake air temperature (IAT) sensor 2 is more than -10°C (14°F) at start-up. |
| • | The manifold absolute pressure (MAP) is within a specified range for a calculated engine load. |
| • | DTC P0301-P0306 runs continuously once the above conditions are met. |
Condition 1 for Setting the DTC
The PCM detects 30-100 misfires every 200 engine revolutions depending on engine speed and engine load.
Condition 2 for Setting the DTC
The PCM detects 70 misfires every 1,000 engine revolutions.
Action Taken When the DTC Sets
Condition 1
| • | The PCM flashes the malfunction indicator lamp (MIL) the first time the diagnostic fails indicating that catalytic converter damage can occur. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame data. |
Condition 2
| • | The PCM illuminates the MIL the second time the diagnostic fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame data. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present. |
| • | The DTC will clear if there is no misfire detected when the vehicle is operated in the same condition that the misfire was originally set. |
| • | A DTC can be cleared by using the scan tool Clear DTC Information function. |
Diagnostic Aids
Check for any of the following conditions:
| • | If any DTCs other than misfire P0300-P0306 are set, diagnose those DTCs first. |
| • | An intermittent ignition system malfunction may cause DTC P0301-P0306 to set. Check ignition system performance with an engine oscilloscope. |
| • | Review the misfire counters located in the Engine Data list of the scan tool while the engine is running. Misfire activity can be monitored with the scan tool in the Misfire Current Cyl # data list parameter of the appropriate cylinder. Use this information in order to determine if the fault is present or an intermittent malfunction. |
| • | An intermittent can also be the result of a defective CKP sensor signal rotor. Inspect the CKP signal rotor for nicks, dents, missing teeth, and foreign material. |
| • | Check for engine overheating. Refer to Engine Overheating in Engine Cooling. |
An intermittent malfunction may be caused by a fault in the electrical circuits of the ignition system or fuel system of the misfiring cylinder. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .
Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.
The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||||||||||
2 | Were you sent here from DTC P0300? | -- | Go to Step 3 | Go to DTC P0300 | ||||||||
3 |
Did you find a condition with the ignition coil boot? | -- | Go to Step 12 | Go to Step 4 | ||||||||
4 |
Does the spark tester spark and is the spark consistent? | -- | Go to Step 5 | |||||||||
5 |
Does the spark plug appear to be OK? | -- | Go to Step 9 | Go to Step 6 | ||||||||
6 | Is the spark plug oil or coolant fouled? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical - 3.5L (L66) | Go to Step 7 | ||||||||
7 | Is the spark plug gas fouled? | -- | Go to Step 10 | Go to Step 8 | ||||||||
8 | Does the spark plug show any signs of being cracked, worn, or incorrectly gap? | -- | Go to Step 11 | Go to Step 9 | ||||||||
9 |
Did the misfire move with the spark plug? | -- | Go to Step 11 | Go to Step 10 | ||||||||
10 |
Important:
Perform the fuel injector coil test. Refer to Fuel Injector Solenoid Coil Test . Did you find and correct the condition? | -- | Go to Step 13 | Go to Symptoms - Engine Mechanical in Engine Mechanical - 3.5L (L66) | ||||||||
11 | Replace the spark plug. Refer to Spark Plug Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||
12 | Replace the ignition coil. Refer to the appropriate procedure: Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||
13 | Was the customer's concern that the MIL is flashing? | -- | Go to DTC P0420 or P0430 | Go to Step 14 | ||||||||
14 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 | ||||||||
15 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||
