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 3-way catalytic converter damage. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for catalytic converter damage are present. If the misfire rate is 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 P0107, P0108, P0122, P0123, P0336, P0337, P0341, and P0342 are not set. |
| • | The engine speed is less than 4,500 RPM. |
| • | The fuel tank level is more than 20 percent. |
| • | No anti-jerk correction |
| • | No rough road detection |
| • | No crankshaft oscillation detection |
Conditions for Setting the DTC
The ECM detects a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed a predetermined value.
Action Taken When the DTC Sets
| • | The MIL will illuminate after 3 consecutive trips with a failure or the MIL will flash. |
| • | A history DTC is stored. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for 10 seconds. |
Diagnostic Aids
| • | A misfire DTC could be caused by an excessive vibration from sources other than the engine. Inspect for the following possible sources: |
| - | A tire or wheel that is out of round or out of balance |
| - | Variable thickness brake rotors |
| - | An unbalanced drive shaft |
| - | Certain rough road conditions |
| - | A damaged accessory drive component or belt |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Step | Action | Values | Yes | No | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | |||||||||||||||||
2 |
Important: The engine may only misfire when the engine is under a load. An engine load may be necessary to verify the condition.
Does DTC P0300 set? | -- | Go to Step 4 | Go to Step 3 | ||||||||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||||||||||
4 |
Important: Excessive vibration from other sources than the engine, or mechanical engine condition can cause a misfire DTC to set. For example, an accessory drive belt could cause this condition. Is the engine misfiring? | -- | Go to Step 5 | Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.2L | ||||||||||||||||
5 | Are DTCs P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0335, 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 - 1.2L | Go to Step 7 | ||||||||||||||||
7 |
Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 8 | ||||||||||||||||
8 |
Important: The companion cylinders are 1/4 and 2/3. Does the spark jump the tester gap for each cylinder? | -- | Go to Step 10 | Go to Step 9 | ||||||||||||||||
9 |
Is the spark plug wire resistance less than the specified value? | 1000 ohms per 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 coolant or oil fouled? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.2L | Go to Step 13 | ||||||||||||||||
13 | Is the spark plug gas fouled? | -- | Go to Step 16 | Go to Step 14 | ||||||||||||||||
14 | Does 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 - 1.2L | ||||||||||||||||
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 - 1.2L | ||||||||||||||||
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) was 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 | Are any DTCs displayed that have not been diagnosed? | -- | System OK |
