Circuit 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 Descriptors
This diagnostic procedure supports the following DTC.
DTC P0300 Engine Misfire Detected
Conditions for Running the DTC
| • | DTC P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0125, P0128, P0335, P0336, P0341, P0342, P0343, P0500, P0502, P0503, P1114, P1115, P1120, and P1220 are not set. |
| • | The engine speed is between 400-5,600 RPM. |
| • | The ignition voltage is between 11-18 volts. |
| • | The engine coolant temperature (ECT) is between -7 and +130°C (19-266°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. |
| • | DTC P0300 runs continuously once 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 Symptoms - Propeller Shaft in Propeller Shaft. |
| - | Worn or damaged accessory drive belt--Refer to Base Engine Misfire without Internal Engine Noises 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. |
| • | 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 numbers below refer to the step numbers on the diagnostic table.
-
If the actual CKP variation values are not within the learned values, the misfire counters may increment.
-
DTC P0135 or P0155 can be set because of a misfire.
Step | Action | Values | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | 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 current misfire counters incrementing? | -- | Go to Step 3 | Go to Diagnostic Aids | |||||||||||||
Are any DTCs other than P0300, P0135 or P0155 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 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? | 700 ohms | 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 | Are the spark plugs oil or coolant fouled? | -- | Go to Step 13 | |||||||||||||
13 | Are the spark plugs gas fouled? | -- | Go to Step 16 | Go to Step 14 | ||||||||||||
14 | Do the spark plugs 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 | |||||||||||||
16 | Perform the fuel system diagnosis. Refer to Fuel System Diagnosis . Did you find and correct the condition? | -- | Go to Step 20 | |||||||||||||
17 | Replace or gap the spark plug. Refer to Spark Plug Replacement . If an improper gap is found, be sure to gap the spark plugs using a wire type gage. Did you complete the replacement? | -- | Go to Step 20 | -- | ||||||||||||
18 | Replace the faulty spark plug. Refer to Spark Plug Replacement . Did you complete the replacement? | -- | Go to Step 20 | -- | ||||||||||||
19 | Replace the faulty spark plug wire. Refer to Spark Plug Wire Replacement . Did you complete the replacement? | -- | Go to Step 20 | -- | ||||||||||||
20 | Was the customer concern the MIL flashing? | -- | Go to Step 21 | Go to Step 22 | ||||||||||||
21 |
Does the DTC run and pass? | 2,500 RPM | Go to Step 22 | Go to DTC P0420 or P0430 | ||||||||||||
22 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 23 | ||||||||||||
23 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
