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, DTC P0300 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, P0315, P0336, P0337, P0341, P0342, and P0502 are not set. |
| • | 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 4 percent. |
| • | 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 third 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 | Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.4L (DOHC) | |||||||||||||
5 | Are DTCs P0201, P0202, P0203, P0204, P0315, P0336, P0337, P0351, or P0352 set? | -- | Go to Step 6 | |||||||||||||
6 | Is there an abnormal engine noise? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.4L (DOHC) | Go to Step 7 | ||||||||||||
7 | Inspect the following components:
Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 8 | ||||||||||||
8 |
Important: An erratic or inconsistent spark is considered a no spark. Does the spark jump the tester gap? | Go to Step 10 | Go to Step 9 | |||||||||||||
9 |
Is the spark plug wire resistance less than the specified value? | 1,000 ohms per 30 cm (per ft) | Go to Step 19 | |||||||||||||
10 |
Does the spark plug appear to be OK? | -- | Go to Step 11 | Go to Step 12 | ||||||||||||
11 |
Did the misfire move with the spark plug? | -- | Go to Step 18 | Go to Step 15 | ||||||||||||
12 | Is the spark plug oil or coolant fouled? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.4L (DOHC) | Go to Step 13 | ||||||||||||
13 | Is the spark plug gas fouled? | -- | Go to Step 16 | Go to Step 14 | ||||||||||||
14 | Did the spark plug show any signs of being cracked, worn, or improperly gapped? | -- | Go to Step 17 | Go to Step 15 | ||||||||||||
15 | Perform the fuel injector coil test. Refer to Fuel Injector Solenoid Coil Test . Did you find and correct the condition? | -- | Go to Step 20 | Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.4L (DOHC) | ||||||||||||
16 | Perform the fuel system diagnosis. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 20 | Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.4L (DOHC) | ||||||||||||
17 | Replace or gap the spark plug. Refer to Spark Plug Replacement . Did you complete the action? | -- | Go to Step 20 | -- | ||||||||||||
18 | Replace the spark plug. Refer to Spark Plug Replacement . Did you complete the replacement? | -- | Go to Step 20 | -- | ||||||||||||
19 | Replace the spark plug wires. Refer to Spark Plug Wire Replacement . Did you complete the replacement? | -- | Go to Step 20 | -- | ||||||||||||
20 | Was the customer concern the malfunction indicator lamp (MIL) flashing? | -- | Go to Step 21 | Go to Step 22 | ||||||||||||
21 | Operate the vehicle within the Conditions for Running the DTC P0420 as specified in the supporting text. Refer to DTC P0420 . Did the DTC run and pass? | Go to Step 22 | Go to DTC P0420 | |||||||||||||
22 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 23 | ||||||||||||
23 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
