System Description
The engine control module (ECM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor 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.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0300 Engine Misfire Detected
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0128, P0220, P0315, P0335, P0336, P0341, P0502, P0503, P1258 are not set. |
| • | The engine speed is between 425-6,200 RPM. |
| • | The ignition voltage is between 9-18 volts. |
| • | The engine coolant temperature (ECT) is between -7 and +130°C (+19 and +266°F). |
| • | The fuel level is more than 10 percent. |
| • | The throttle angle is steady within 1 percent. |
| • | The antilock brake system (ABS) and the traction control system (TCS) are 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 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
| • | Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration: |
| - | Thickness variation of the brake rotors--Refer to Symptoms - Hydraulic Brakes . |
| - | Excessive driveline vibration--Refer to Vibration Analysis - Road Testing . |
| - | Worn or damaged accessory drive belt--Refer to Symptoms - Engine Mechanical . |
| • | There may be more or less cylinders actually misfiring than indicated by the scan tool. |
| • | Spray water on the secondary ignition components using a spray bottle. Look and listen for arcing or misfiring. |
| • | If there are multiple misfires on only one bank, inspect the fuel injector and ignition coil, power and ground circuits for that bank. Refer to Engine Controls Schematics . |
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 | |||||||||||||
|
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 Diagnostic Aids | |||||||||||||
3 | Are any other DTCs set? | -- | Go to Step 4 | |||||||||||||
4 | Can any abnormal engine noise be heard? | -- | Go to Step 5 | |||||||||||||
5 | Does the scan tool indicate that the heated oxygen sensor (HO2S) bank 1 sensor 1 or HO2S bank 2 sensor 1 voltage parameters are below the specified value? | 200 mV | Go to DTC P0131 or P0151 | Go to Step 6 | ||||||||||||
6 | Does the scan tool indicate that the HO2S bank 1 sensor 1 or HO2S bank 2 sensor 1 voltage parameters are fixed above the specified value? | 900 mV | Go to DTC P0132 or P0152 | Go to Step 7 | ||||||||||||
7 | Inspect the following components:
Did you find and correct the condition? | -- | Go to Step 19 | 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 resistance within the specified value? | 188-312 ohms | Go to Step 18 | |||||||||||||
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 17 | Go to Step 15 | ||||||||||||
12 | Is the spark plug oil or coolant fouled? | -- | 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 19 | |||||||||||||
16 | Perform the fuel system diagnosis. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 19 | |||||||||||||
17 | Replace the faulty spark plug. Refer to Spark Plug Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- | ||||||||||||
18 | Replace the faulty spark plug wires. Refer to Spark Plug Wire Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- | ||||||||||||
19 | Was the customer concern the malfunction indicator lamp (MIL) flashing? | -- | Go to Step 20 | Go to Step 21 | ||||||||||||
20 |
Does the DTC run and pass? | 2,500 RPM | Go to Step 21 | Go to DTC P0420 or P0430 | ||||||||||||
21 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 22 | ||||||||||||
22 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
