For 1990-2009 cars

### Description

The engine control module (ECM) 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 ECM is able to detect individual misfire events. A misfire rate that is high enough can cause 3-way catalytic converter damage. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for catalytic converter damage are preset. DTCs P0301-P0306 correspond to cylinders 1-6. If the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder sets.

### DTC Descriptors

This diagnostic procedure supports the following DTCs:

#### Conditions 1

• | DTCs P0121, P0122, P0123, P0221, P0222, P0223, P0335, P0336, or P0338 are not set.

• | The engine speed is between 420-7,000 RPM and steady.

• | The delivered torque signal is more than 12 percent at idle.

• | The delivered torque signal is between 10.5-29.3 percent with the transmission in drive.

• | The intake air temperature (IAT) is more than 30°C (-22°F).

• | The fuel level is more than 11.6 percent, or the fuel level is less than 11.6 percent and misfire MIL is turned ON.

• | Or fuel level scan tool DTC P0461, P0462, P0463, P2067, P2066 or P2068 have been set.

• | The antilock brake system/traction control system (ABS/TCS) is not active.

• | The ECM is not receiving a rough road signal.

• | The fuel cut-off is not active, including the traction control, the deceleration, the high vehicle speed, and the high engine speed.

• | The change in engine speed per second is less than 200-362 RPM.

• | The change in volumetric efficiency per round is less than 225-1,350 percent.

• | After start the engine, there is cylinder ignition at least 6 times.

• | The clutch pedal press/release change has a problem.

• | The ECM detects that the fuel leaks test procedure has closed.

• | The engine reverse control system is inactive.

• | DTC P0300 runs continuously when the above conditions exist for at least 1,000 engine revolutions.

• | When a misfire rate high enough causes 3-way catalytic converter damage, the above conditions are met except for the follow:

• | The first test interval delays to 1,000 engine revolutions.

• | The engine coolant temperature is less than 47°C (116.6°F).

• | The fuel level is more than 11.6 percent.

• | Or fuel level is less than 11.6 percent, the malfunction indicator lamp flashes not for the first time.

• | DTC P0300 runs continuously when the above conditions exist for at least 1,000 engine revolutions.

### Conditions for Setting the DTC

• | The ECM detects a crankshaft rotation speed variation indicating a misfire rate of 1.82 percent, which is sufficient to cause emissions levels to exceed mandated standards.

| OR

• | The ECM detects a crankshaft rotation speed variation indicating a misfire rate of 1.81-5 percent, which is sufficient to cause 3-way catalytic converter damage.

• | The condition exists for more than 4 seconds.

### 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 4 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

• | A misfire DTC could be caused by an excessive vibration from sources other than the engine. Check for the following possible sources:

- | A tire or wheel that is out of round or out of balance

- | Variable thickness brake rotor or drum

- | Drive shaft not balanced

- | Certain rough road conditions

- | Damaged accessory drive belt

• | For an intermittent condition, refer to Intermittent Conditions .

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Were you sent here from DTC P0300? | Go to Step 3 | Go to DTC P0300
3 |

1. Turn OFF the ignition.
2. Remove the ignition coil of the misfiring cylinder, but leave the electrical connector connected. Refer to the appropriate procedure:

• | Ignition Coil Replacement - Bank 1

• | Ignition Coil Replacement - Bank 2

3. Inspect the ignition coil boot for the following conditions:

• | Holes

• | Tears

• | Carbon tracking

• | Oil contamination or water intrusion

Did you find a condition with the ignition coil boot?

Go to Step 12

Go to Step 4

4 |

Important: The fuel pump fuse is located under the right rear seat. The carpet must be lifted up to access the rear fuse block.

1. Remove the fuel pump fuse from the right rear fuse block.
2. Install the J 26792 Spark Tester to the ignition coil boot and a good ground.
3. Crank the engine while observing the J 26792 .

Does the spark tester spark and is the spark consistent?

Go to Step 5

Go to Electronic Ignition (EI) System Diagnosis

5 |

1. Turn OFF the ignition.
2. Remove the spark plug from the cylinder that indicated a misfire.
3. Inspect the spark plug. Refer to Spark Plug Inspection .

Does the spark plug appear to be OK?

Go to Step 9

Go to Step 6

6 | Is the spark plug oil or coolant fouled? | Go to Symptoms - Engine Mechanical | Go to Step 7
7 | Is the spark plug gas fouled? | Go to Step 10 | Go to Step 8
8 | Does the spark plug show any signs of being cracked, worn, or incorrectly gap? | Go to Step 11 | Go to Step 9
9 |

1. Swap the suspected spark plug with another cylinder that is operating correctly.
2. Start the engine.
3. Operate the engine within the conditions that the misfire occurred.
4. Monitor the Misfire current counters with a scan tool.

Did the misfire move with the spark plug?

Go to Step 11

Go to Step 10

10 | Important:

• | Make sure all the fuel injectors operate. High resistance in a fuel injector circuit causes the fuel injector to be inoperative without setting a fuel injector DTC.

• | Return to this diagnostic after you complete the Fuel Injector Coil Test.

Perform the fuel injector coil test. Refer to Fuel Injector Solenoid Coil Test .

Did you find and correct the condition?

Go to Step 13

Go to Symptoms - Engine Mechanical

11 | Replace the spark plug. Refer to Spark Plug Replacement . Did you complete the replacement? | Go to Step 13 | --
12 | Replace the ignition coil. Refer to Ignition Coil Replacement - Bank 1 and Ignition Coil Replacement - Bank 2 . Did you complete the replacement? | Go to Step 13 | --
13 | Was the customer's concern that the malfunction indicator lamp (MIL) is flashing? | Go to DTC P0420 or P0430 | Go to Step 14
14 |

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 15

15 | 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 | System OK