System Description
The powertrain control module (PCM) 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 PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic converter (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0300 Engine Misfire Detected
Conditions for Running the DTC
| • | DTCs P0107, P0112, P0113, P0117, P0118, P0120, P0121, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0220, P0336, P0502, P0506, P0507, P0601, P1133, P1621, P2135 are not set. |
| • | The engine speed is between 469-6,400 RPM. |
| • | The ignition voltage is between 9-17 volts. |
| • | The engine coolant temperature (ECT) is between -7°C and +123°C (20-254°F). |
| • | The engine has been running for more than 5 seconds. |
| • | The throttle position (TP) has not increased more than 8 percent in 1 second. |
| • | The TP has not decreased more than 1.5 percent in 1 second. |
| • | DTC P0300 runs continuously when the above conditions are met. |
Conditions for Setting the DTC
The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.
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 3 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
You must perform the CKP system variation learn procedure before proceeding with the diagnostic table. Refer to Crankshaft Position System Variation Learn .
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||||
Are any of the Misfire Current counters incrementing? | -- | Go to Step 3 | Go to Intermittent Conditions | |||||||||||
3 | Are any other DTCs set? | -- | Go to Step 4 | |||||||||||
4 | Can any abnormal engine noise be heard? | -- | Go to Step 5 | |||||||||||
5 |
Is the indicated value more than the typical value? | -- | Go to DTC P0108 | Go to Step 6 | ||||||||||
6 | Inspect the following components:
Did you find and correct the condition? | -- | Go to Step 20 | Go to Step 7 | ||||||||||
7 |
Does the spark tester spark? | -- | Go to Step 9 | Go to Step 8 | ||||||||||
8 | Inspect the affected cylinder spark plug boot for a missing or damaged ignition coil spring. Did you find and correct the condition? | -- | Go to Step 16 | |||||||||||
9 |
Does the spark plug appear to be OK? | -- | Go to Step 10 | Go to Step 11 | ||||||||||
10 |
Did the misfire move with the spark plug? | -- | Go to Step 17 | Go to Step 14 | ||||||||||
11 | Is the spark plug oil or coolant fouled? | -- | Go to Step 12 | |||||||||||
12 | Is the spark plug gas fouled? | -- | Go to Step 15 | Go to Step 13 | ||||||||||
13 | Did the spark plug show any signs of being cracked, worn, or improperly gapped? | -- | Go to Step 16 | Go to Step 14 | ||||||||||
14 | Perform the fuel injector coil test. Refer to Fuel Injector Diagnosis . Did you find and correct the condition? | -- | Go to Step 18 | |||||||||||
15 | Perform the fuel system diagnosis. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 18 | |||||||||||
16 | Replace or gap the spark plug. Refer to Spark Plug Replacement . Did you complete the action? | -- | Go to Step 18 | -- | ||||||||||
17 | Replace the faulty spark plug. Refer to Spark Plug Replacement . Did you complete the replacement? | -- | Go to Step 18 | -- | ||||||||||
18 | Was the customer concern the MIL flashing? | -- | Go to Step 19 | Go to Step 20 | ||||||||||
19 |
Does the DTC run and pass? | 2,500 RPM | Go to Step 20 | Go to DTC P0420 | ||||||||||
20 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 21 | ||||||||||
21 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
