GM Service Manual Online
For 1990-2009 cars only

Object Number: 211171  Size: LF
Engine Controls Components
Cell 20: Ignition Controls
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

System Description

The Powertrain Control Module (PCM) monitors both the crankshaft and camshaft position in order to detect engine misfire. The PCM looks for the rapid decrease in crankshaft speed associated with engine misfire once every 100 camshaft revolutions. The PCM may require that several consecutive misfire conditions are detected before storing this DTC and illuminating the MIL. Under light misfire conditions, the PCM may require more than one trip to set this DTC. Under severe misfire, the PCM flashes the MIL. A flashing MIL signals that a misfire capable of damaging the catalytic converter is detected. The Torque Converter Clutch is disabled momentarily to determine if the misfire was due to a rough road condition (automatic transmission only).

Conditions for Running the DTC

    • DTCs P0105, P0107, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0325, P0335, P0341, P0342, P0502, P0503, P0506, P0507, P0601, P0740, P0742, P1133, and P1621 are not set.
    • The engine speed is between 469-5900 RPM.
    • The battery voltage is between 9-17 volts.
    • The engine coolant temperature (ECT) is between -7°C and +123°C (20°-254°F).
    • The engine has been running more than 5 seconds.
    • The throttle position (TP) has not increased more than 8 percent in 1 second.
    • The throttle position (TP) has not decreased more than 1.5 percent in 1 second.

Conditions for Setting the DTC

The misfire total is more than 8 counts.

Action Taken When the DTC Sets

The Malfunction Indicator Lamp (MIL) will illuminate if the fault is active within the same conditions for two out of eighty ignition cycles when there is misfire.

OR

The MIL will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.

OR

    • The MIL will illuminate immediately and flash if a misfire is severe enough to cause catalyst damage.
    • The Torque Converter Clutch (TCC) will disable whenever a misfire is being detected with or without a misfire DTC set (automatic transmission only).
    • The PCM will record the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers will store this information.
    • A history DTC is stored.

Conditions for Clearing the MIL/DTC

    • The MIL will turn off after 3 consecutive ignition cycles in which the diagnostic runs without a fault within the freeze frame conditions that the DTC failed.
    • A history DTC will clear after 40 consecutive warm up cycles without a fault.
    • A scan tool can clear the DTCs.

Diagnostic Aids

An intermittent DTC can also be the result of a defective reluctor wheel. Remove the crankshaft sensor and inspect the reluctor wheel through the crankshaft sensor mount hole. Check the porosity and the condition of the reluctor wheel.

Whenever the DTC is an intermittent, refer to the Driveability Symptom Tables.

Perform the fuel Injector Balance Test. Refer to Fuel Injector Balance Test .

Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

  1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored in the scan tool for later reference.

  2. Whenever a DTC P0108 is present, verify that no misfire is present by viewing the misfire counters. DTC P0108 may set as a result of a misfire.

  3. A visual/physical inspection should include checking the following conditions:

  4. • The wiring for proper connections, pinches and cuts.
    • Clean and tight PCM grounds.
    • The vacuum hoses for splits, kinks and proper connections as shown on the Vehicle Emission Information label. Check thoroughly for any type of leak or restriction.
  1. This step determines if the Misfire DTC is the result of a hard malfunction or an intermittent condition

  2. When the misfire is not present, operate the vehicle to the conditions found in the Freeze Frame Data in order to detect misfire. Depending on the engine load, the conditions may have to be maintained for up to 20 seconds. Whenever the misfire accumulators start to increment, then the misfire is present. A history misfire counter will store the number of misfires that have occurred until the DTC is cleared. The current counter must count a total of at least 195 misfires before writing to the history counter.

  3. No spark on one coil may be caused by an open secondary circuit. Therefore, the coils secondary resistance should be checked.

  4. Use the injector test lamp to test the harness wiring and for PCM control of the injectors.

  5. Perform the Fuel Inj Coil Test on the misfiring cylinder only.

  6. Determines if the injector driver circuit is shorted to ground, voltage or if the PCM is malfunctioning.

  7. Replacement PCMs must be programmed and the crankshaft position system variation procedure must be performed. Refer to the latest Techline information for PCM programming.

  8. Replace any spark plugs that are worn, cracked or fouled. Refer to Engine Mechanical portion of the service manual if any plugs are fouled or damaged due to an engine mechanical failure.

  9. Since the voltage is supplied to the injector on a single circuit before the injector harness, the malfunction could only be a poor connection or an open in the injector harness. An open before the harness would result in a Cranks But Does Not Run complaint.

  10. A basic engine problem that affects only a single cylinder is possible at this point (i.e. valve train, compression, etc.).

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Refer to the Test Description for additional information.

Are any component DTCs set?

--

Go to DTC Tables first

Go to Step 3

3

  1. Perform a visual/physical inspection.
  2. Make any necessary repairs.

Were any repairs necessary?

--

Go to Step 6

Go to Step 4

4

With the engine idling, install a scan tool.

Is the misfire current counter incrementing on the cylinder that had a misfire DTC?

--

Go to Step 5

Go to Step 6

5

  1. Turn the engine OFF
  2. Disconnect the fuel injector harness connectors.
  3. Install the J 26792 spark tester on the spark plug cable for the cylinder that indicated a misfire.
  4. Remove the spark plug cable from the cylinder on the same ignition coil housing and install a jumper wire from the spark plug connector of the ignition coil housing to ground.
  5. Crank the engine with the remaining spark plugs cables still connected.

Does the spark tester spark?

--

Go to Step 8

Go to Step 9

6

  1. Turn the ignition ON leaving the engine OFF.
  2. Review the Freeze Frame data and note parameters.
  3. Operate vehicle within the Freeze Frame conditions and conditions for setting the DTC as noted.

Is the misfire current counter incrementing on the cylinder that indicated a misfire?

--

Go to Step 5

Go to Step 7

7

Was a repair made from the visual/physical inspection?

--

Go to Step 30

Go to Diagnostic Aids

8

  1. Remove the spark plug from the mifiring cylinder.
  2. Change the spark plug with a spark plug from a known good cylinder.
  3. Reconnect the fuel injector harness connector.
  4. Run the vehicle within the misfire conditions as noted from the Freeze Frame data.

Is the misfire current counter incrementing on the cylinder that indicated a misfire?

--

Go to Step 13

Go to Step 22

9

  1. Remove the spark plug cable from the misfiring cylinder.
  2. Use a J 39200 DMM in order to measure the resistance of the spark plug cable.

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

1,000ohms/inch

Go to Step 10

Go to Step 23

10

  1. Remove the ignition coil from the cylinder that did not fire.
  2. Use a J 39200 DMM in order to measure the ignition coils secondary resistance.

Is the resistance within the specified range?

5-8 K ohms

Go to Step 11

Go to Step 24

11

  1. Replace the ignition coil with a known good one.
  2. Crank the engine and check for spark.

Did spark occur on the spark tester?

--

Go to Step 24

Go to Step 12

12

  1. Visually inspect the ICM 6 pin harness connector to see if the connections are clean and tight.
  2. Make any necessary repairs. Refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Were any repairs necessary?

--

Go to Step 30

Go to Step 25

13

  1. Turn the engine OFF.
  2. Disconnect the 4 fuel injector harness connectors from the injectors.
  3. Install an injector test lamp on the injector harness connector for the misfirng cylinder.
  4. Crank the engine and note the lamp.

Does the fuel injector test lamp blink?

--

Go to Step 14

Go to Step 15

14

Perform the Injector Coil/Balance Test Procedure . Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) .

Is the fuel injector OK for the cylinder that had indicated a misfire?

--

Go to Step 28

Go to Step 29

15

  1. Disconnect the fuel injector test lamp.
  2. Connect a test lamp to ground, probe the misfiring cylinder fuel injector harness connector ignition positive voltage terminal.
  3. Crank the engine.

Did the test lamp illuminate?

--

Go to Step 16

Go to Step 27

16

  1. Connect a test lamp to ground.
  2. Disconnect the fuel injector harness connectors.
  3. Turn ON the ignition leaving the engine OFF.
  4. Probe the fuel injector harness connector control circuit terminal for the cylinder that indicated a misfire.

Did the test lamp remain OFF?

--

Go to Step 17

Go to Step 26

17

  1. Connect the test lamp to B+.
  2. Probe the fuel injector control circuit terminal.

Did the test lamp remain OFF?

--

Go to Step 18

Go to Step 19

18

Inspect the fuel injector harness connector and the PCM harness connectors and connections for an open circuit.

Are the connections OK?

--

Go to Step 20

Go to Step 21

19

  1. Check for a short to ground in the fuel injector control circuit for the cylinder that indicated a misfire.
  2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 30

Go to Step 20

20

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 30

--

21

Repair the connector or connections. Refer to Connector Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 30

--

22

Replace the malfunctioning spark plug. Refer to Spark Plug Replacement in Engine Electrical.

Is the action complete?

--

Go to Step 30

--

23

Replace the spark plug cable. Refer to Spark Plug Wire Harness Replacement in Engine Electrical.

Is the action complete?

--

Go to Step 30

--

24

Replace the defective ignition coil. Refer to Ignition Coil and Ignition Coil Module Replacement .

Is the action complete?

--

Go to Step 30

--

25

Replace the ICM. Refer to Ignition Coil and Ignition Coil Module Replacement .

Is the action complete?

--

Go to Step 30

--

26

  1. Check for a short to voltage in the misfiring cylinder fuel injector control circuit.
  2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 30

Go to Step 20

27

Repair the open ignition positive voltage circuit for the fuel injector. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 30

--

28

Check for a basic engine problem, refer to Base Engine Misfire Diagnosis in Engine Mechanical.

Is the action complete?

--

Go to Step 30

--

29

Replace the malfunctioning fuel injector. Refer to Fuel Injector Replacement .

Is the action complete?

--

Go to Step 30

--

30

  1. Using the scan tool, clear DTCs
  2. Start the engine and idle at normal operating temperature
  3. Operate the vehicle within the conditions for setting this DTC as supported in the text.

Does the scan tool indicate that this diagnostic ran and passed?

--

Go to Step 31

Go to Step 2

31

Check if any additional DTCs are set.

Are any DTCs displayed that have not been diagnosed?

--

Go to the applicable DTC table

System OK