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, this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0300 Engine Misfire Detected
Conditions for Running the DTC
| • | DTCs P0106, P0107, P0108, P0117, P0118, P0122, P0123, P0317, P0336, P0337, P0341, P0342, and P0502 are not set. |
| • | The engine is operating for more than 10 seconds. |
| • | The camshaft position sensor is sychronized with the crankshaft. |
| • | The engine speed is between 600-6,500 RPM and steady. |
| • | The ignition 1 voltage is between 11-16 volts. |
| • | The engine coolant temperature (ECT) is between -7°C and +120°C (+19°F and +248°F). |
| • | The fuel level is more than 15 percent. |
| • | The throttle angle is steady within 3 percent. |
| • | The throttle angle is less than 3 percent when the vehicle speed is more than 10 km/h (6 mph) |
| • | The antilock brake system (ABS) and the traction control system (TCS), if equipped, is not active. |
| • | The torque management is not active. |
| • | The transmission is not changing gears. |
| • | The A/C clutch is not changing states. |
| • | The ECM is not in fuel shut-off or decel fuel cut-off mode. |
| • | The ECM is not receiving a rough road signal. |
| • | DTC P0300 runs continuously when the above conditions are met. |
Conditions for Setting the DTC
The ECM detects a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed a predetermined value.
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 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
Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration:
| • | A tire or wheel that is out of round or out of balance |
| • | Variable thickness brake rotors |
| • | A unbalanced or damaged driveline condition |
| • | Certain rough road conditions |
| • | Worn or damaged accessory drive component or 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 | |||||||||||||||||
|
Important: A misfire may only occur when the engine is under a load. An engine load may be necessary to verify the condition.
Are any of the Misfire Current Cylinder counters incrementing? | -- | Go to Step 4 | Go to Step 3 | |||||||||||||||||
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | |||||||||||||||||
Is the engine misfiring? | -- | Go to Step 5 | ||||||||||||||||||
5 | Are DTCs P0201, P0202, P0203, P0204, P0317, P0336, P0337, P0341, P0342, P0351, or P0352 set? | -- | Go to Step 6 | |||||||||||||||||
6 | Is there an abnormal engine noise? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.8L (L79) | Go to Step 7 | ||||||||||||||||
7 | Is there more than one cylinder specific misfire DTC set? | -- | Go to Step 8 | Go to DTC P0301-P0304 | ||||||||||||||||
8 | Are there any heated oxygen sensor (HO2S) DTCs Set? | -- | Go to Step 9 | |||||||||||||||||
9 | Inspect the following components:
Did you find and correct the condition? | -- | Go to Step 10 | Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.8L (L79) | ||||||||||||||||
10 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 11 | ||||||||||||||||
11 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
