System Description
The engine control module (ECM) 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 ECM is able to detect individual misfire events. A misfire rate that is high enough can cause overheating and damage to the 3-way catalytic converter (TWC) under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC damage are present. If the ECM detects a misfire rate sufficient to cause emission levels to exceed a predetermined value, and the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder sets.
DTC Descriptor
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 |
Conditions for Setting the DTC
| • | DTCs P0106, P0107, P0108, P0117, P0118, P0122, P0123, P0336, P0337, P0341, P0342, and P0502 are not set. |
| • | The emission threshold is 3 percent. |
| • | Twenty engine cycles have occurred since cranking has started. |
| • | The A/C compressor clutch has not just engaged or disengaged. |
| • | The engine load and engine speed are in a detectable region and are at or above 0 torque. |
| • | The camshaft position (CMP) sensor is in synchronization. |
| • | The exhaust gas recirculation (EGR) flow diagnostic is not in progress. |
| • | The fuel level is greater than 12 percent of the rated tank capacity. |
| • | The decel fuel cutoff (DFCO) is not active. |
| • | The throttle position change is less than 3 percent per 125 milliseconds. |
| • | The vehicle has not encountered an abusive engine speed of 7,000 RPM. |
| • | The crankshaft speed patterns are normal. |
| • | The throttle position is less than 3 percent when the vehicle speed is greater than 10 km/h (6 mph). |
| • | The vehicle voltage is between 11-16 volts. |
| • | The engine coolant temperature (ECT) is between -7°C to +120°C (+19°F to +248°F). |
| • | There is the correct ratio between the crankshaft position (CKP) sensor pulses and the CMP sensor pulses. |
Conditions for Setting the DTC
The ECM detects a crankshaft rotation speed variation indicating a single cylinder misfire rate sufficient to cause emissions levels to exceed mandated standards.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 4 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
| • | 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 |
| - | Certain rough road conditions |
| - | Damaged accessory drive belt |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | 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 |
Important: If the spark tester sparks once or twice and then quits, this is considered no spark. Does the J 26792 spark and is the spark consistent? | -- | Go to Step 4 | Go to Step 5 | ||||
4 |
Does the spark plug appear to be OK? | -- | Go to Step 9 | Go to Step 6 | ||||
Is the spark plug wire resistance less than the specified value, but more than zero? | 1,000 ohms per 30 cm (per ft) | Go to Step 12 | ||||||
6 | Is the spark plug oil or coolant fouled? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.8L (L79) | 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 gapped? | -- | 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 - 1.8L (L79) | ||||
11 | Replace the spark plug. Refer to Spark Plug Replacement Did you complete the replacement? | -- | Go to Step 13 | -- | ||||
12 |
Important: An open or failed spark plug wire could cause damage to the ignition coil. Verify that the ignition coil can fire the J 26792 for the affected cylinder after the spark plug wire is replaced. Replace the spark plug wire. Refer to Spark Plug Wire Replacement Did you complete the replacement? | -- | Go to Step 13 | -- | ||||
13 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 14 | ||||
14 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
