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 P0016, P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0128, P0315, P0335, P0336, P0341, P0502, P0503, P1114, P1115, P1121, are not set. |
| • | The engine speed is between 450-5,000 RPM. |
| • | The ignition voltage is between 10-18 volts. |
| • | The engine coolant temperature (ECT) is between -7 and +130°C (+19 to +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 are not active. |
| • | The transmission is not changing gears. |
| • | The A/C clutch is not changing states. |
| • | The PCM is not in fuel shut-off or decel fuel cut-off mode. |
| • | The PCM is not receiving a rough road signal. |
| • | This diagnostic 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
| • | Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration: |
| - | Variable thickness brake rotors--Refer to Symptoms - Hydraulic Brakes in Hydraulic Brakes. |
| - | Drive shaft not balanced--Refer to Vibration Analysis - Driveline in Vibration Diagnosis and Correction. |
| - | Worn or damaged accessory drive belt--Refer to Symptoms - Engine Mechanical in 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. |
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 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||||||||
|
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 Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | Go to Step 4 | ||||||||||||
4 | Can any abnormal engine noise be heard? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical | 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 20 | Go to Step 8 | ||||||||||||
8 |
Does the spark jump the tester gap, and is the spark consistent? | -- | 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 15 | Go to Step 20 | ||||||||||||
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 19 | Go to Step 16 | ||||||||||||
12 | Are the spark plugs oil or coolant fouled? | -- | Go to Symptoms - Engine Mechanical in Engine Mechanical | Go to Step 13 | ||||||||||||
13 | Are the spark plugs gas fouled? | -- | Go to Step 17 | Go to Step 14 | ||||||||||||
14 | Do the spark plugs show any signs of being cracked, worn, or improperly gapped? | -- | Go to Step 18 | Go to Step 16 | ||||||||||||
15 | Inspect the distributor cap and repair or replace as necessary. Refer to Distributor Inspection . Did you complete the action? | -- | Go to Step 21 | -- | ||||||||||||
16 | Perform the fuel injector coil test. Refer to Fuel Injector Solenoid Coil Test . Did you find and correct the condition? | -- | Go to Step 21 | Go to Symptoms - Engine Mechanical in Engine Mechanical | ||||||||||||
17 | Perform the fuel system diagnosis. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 21 | Go to Symptoms - Engine Mechanical in Engine Mechanical | ||||||||||||
18 | Replace or gap the spark plug. Refer to Spark Plug Replacement . Did you complete the action? | -- | Go to Step 21 | -- | ||||||||||||
19 | Replace the faulty spark plug. Refer to Spark Plug Replacement . Did you complete the replacement? | -- | Go to Step 21 | -- | ||||||||||||
20 | Replace the faulty spark plug wire. Refer to Spark Plug Wire Replacement . Did you complete the replacement? | -- | Go to Step 21 | -- | ||||||||||||
21 | Was the customer concern the malfunction indicator lamp (MIL) flashing? | -- | Go to Step 22 | Go to Step 23 | ||||||||||||
22 |
Does the DTC run and pass? | 2,500 RPM | Go to Step 23 | Go to DTC P0420 or P0430 | ||||||||||||
23 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 24 | ||||||||||||
24 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
