The engine control module (ECM) uses information from the crankshaft position (CKP) sensor and the ignition control (IC) module 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 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 ECM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.
This diagnostic procedure supports the following DTC:
DTC P0300 Engine Misfire Detected
• | DTCs P0068, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0171, P0172, P0220, P0315, P0326, P0327, P0336, P0502, P0507, P0601, P0602, P0604, P0606, P0641, P0651, P0700, P1133, P1134, P1516, P1621, P1680, P1681, P2101, P2120, P2125, P2135, P2138, P2176 are not set. |
• | The engine speed is between 450-6,400 RPM (M/T). |
• | The engine speed is between 450-6,100 RPM (auto). |
• | The ignition voltage is between 9-18 volts. |
• | The engine coolant temperature (ECT) is between -7 and +123°C (+20 and +254°F). |
• | The engine has been running for more that 5 seconds. |
• | The fuel level is more than 10 percent. |
• | DTC P0300 runs continuously when the above conditions are met. |
The ECM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.
• | 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. |
• | 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. |
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 | |||||||||||
Important: You must perform the crankshaft position (CKP) system variation learn procedure before proceeding with this diagnostic table. Refer to Crankshaft Position System Variation Learn .
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 | Inspect the following components:
Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 6 | ||||||||||
6 |
Important: Not grounding the IC module housing may cause an erratic spark. Does the spark tester spark on all cylinders? | -- | Go to Step 7 | |||||||||||
7 |
Does the spark plug appear to be OK? | -- | Go to Step 8 | Go to Step 9 | ||||||||||
8 |
Did the misfire move with the spark plug? | -- | Go to Step 15 | Go to Step 12 | ||||||||||
9 | Is the spark plug oil or coolant fouled? | -- | Go to Step 10 | |||||||||||
10 | Is the spark plug gas fouled? | -- | Go to Step 13 | Go to Step 11 | ||||||||||
11 | Did the spark plug show any signs of being cracked, worn, or improperly gapped? | -- | Go to Step 14 | Go to Step 12 | ||||||||||
12 | Perform the fuel injector coil test. Refer to Fuel Injector Diagnosis . Did you find and correct the condition? | -- | Go to Step 19 | |||||||||||
13 | Perform the fuel system diagnosis. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 16 | |||||||||||
14 | Replace or gap the spark plug. Refer to Spark Plug Replacement . Did you complete the action? | -- | Go to Step 16 | -- | ||||||||||
15 | Replace the faulty spark plug. Refer to Spark Plug Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||||||
16 | Was the customer's concern the malfunction indicator lamp (MIL) flashing? | -- | Go to Step 17 | Go to Step 18 | ||||||||||
17 |
Does the DTC run and pass? | 2,500 RPM | Go to Step 18 | Go to DTC P0420 | ||||||||||
18 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 19 | ||||||||||
19 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |