GM Service Manual Online
For 1990-2009 cars only

System 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 overheating and damage to the 3-way catalytic converter (TWC) under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC damage are present. If the ECM detects a misfire rate sufficient to cause emission levels to exceed a predetermined value, DTC P0300 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0300 Engine Misfire Detected

Conditions for Running the DTC

    • DTCs P0106, P0107, P0108, P0117, P0118, P0122, P0123, P0315, P0336, P0337, P0341, P0342, and P0502 are not set.
    • The engine speed is between 600-6,500 RPM and steady.
    • The ignition 1 voltage is between 11-16 volts.
    • The engine coolant temperature (ECT) is between -7°C and 120°C (19°F and 248°F).
    • The fuel level is more than 15 percent.
    • The throttle angle is steady within 4 percent.
    • The antilock brake system (ABS) and the traction control system (TCS), if equipped, is not active.
    • The torque management is 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 detects a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed a predetermined value.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) on the third 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

Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration:

    • A tire or wheel that is out of round or out of balance
    • Variable thickness brake rotors
    • A unbalanced or damaged driveline condition
    • Certain rough road conditions
    • Worn or damaged accessory drive component or belt

For an intermittent condition, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step determines if there is a current misfire condition. The scan tool will display increasing counts in the Total Misfire Current Counter parameter if a misfire is occurring.

  1. If the Total Misfire Current Counter parameter is incrementing, but the engine is NOT misfiring, this could be caused by an excessive vibration from other sources than the engine.

  1. If the actual CKP variation values are not within the learned values, the Total Misfire Current Counter parameter may increment.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Important: A misfire may only occur when the engine is under a load. An engine load may be necessary to verify the condition.

  1. Turn ON the ignition, with the engine OFF.
  2. Clear the DTCs with a scan tool.
  3. Start the engine.
  4. Monitor the Misfire Current Cylinder counter parameters with a scan tool.

Are any of the Misfire Current Cylinder counters incrementing?

--

Go to Step 4

Go to Step 3

3

  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn the ignition OFF 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 4

Go to Diagnostic Aids

4

Is the engine misfiring?

--

Go to Step 5

Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.4L (DOHC)

5

Are DTCs P0201, P0202, P0203, P0204, P0315, P0336, P0337, P0351, or P0352 set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 6

6

Is there an abnormal engine noise?

--

Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.4L (DOHC)

Go to Step 7

7

Inspect the following components:

    • The vacuum hoses and seals for splits, restrictions, and improper connections.
    • The intake manifold for vacuum leaks
    • The crankcase ventilation system for vacuum leaks.
    • The engine control module (ECM) grounds for corrosion and loose connections.
    • The exhaust system for restrictions--Refer to Restricted Exhaust in Engine Exhaust.
    • The fuel for contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 8

8

    Important: An erratic or inconsistent spark is considered a no spark.

  1. Turn OFF the ignition.
  2. Disconnect the spark plug wire from the spark plug that corresponds to the Misfire Current Cylinder counter parameters that were incrementing. Refer to Spark Plug Wire Replacement .
  3. Install the J 26792 Spark Tester to the boot of the spark plug and a good ground.
  4. Start the engine.

Does the spark jump the tester gap?

 

Go to Step 10

Go to Step 9

9

  1. Remove the spark plug wire for the affected cylinders. Refer to Spark Plug Wire Replacement .
  2. Inspect the spark plug wire. Refer to Spark Plug Inspection .
  3. Measure the resistance of the spark plug wire with a DMM.

Is the spark plug wire resistance less than the specified value?

1,000 ohms per 30 cm (per ft)

Go to Electronic Ignition (EI) System Diagnosis

Go to Step 19

10

  1. Remove the spark plug from the cylinders that indicated a misfire. Refer to Spark Plug Replacement .
  2. Inspect the spark plug. Refer to Spark Plug Inspection .

Does the spark plug appear to be OK?

--

Go to Step 11

Go to Step 12

11

  1. Exchange the suspected spark plug with another cylinder that is operating correctly. Refer to Spark Plug Wire Replacement .
  2. Operate the vehicle under the same conditions that the misfire occurred.

Did the misfire move with the spark plug?

--

Go to Step 18

Go to Step 15

12

Is the spark plug oil or coolant fouled?

--

Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.4L (DOHC)

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 20

Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.4L (DOHC)

16

Perform the fuel system diagnosis. Refer to Fuel System Diagnosis .

Did you find and correct the condition?

--

Go to Step 20

Go to Symptoms - Engine Mechanical in Engine Mechanical - 1.4L (DOHC)

17

Replace or gap the spark plug. Refer to Spark Plug Replacement .

Did you complete the action?

--

Go to Step 20

--

18

Replace the spark plug. Refer to Spark Plug Replacement .

Did you complete the replacement?

--

Go to Step 20

--

19

Replace the spark plug wires. Refer to Spark Plug Wire Replacement .

Did you complete the replacement?

--

Go to Step 20

--

20

Was the customer concern the malfunction indicator lamp (MIL) flashing?

--

Go to Step 21

Go to Step 22

21

Operate the vehicle within the Conditions for Running the DTC P0420 as specified in the supporting text. Refer to DTC P0420 .

Did the DTC run and pass?

 

Go to Step 22

Go to DTC P0420

22

  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 23

23

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK