GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The electronic ignition system uses an individual ignition coil for each cylinder. There are 2 separate ignition module assemblies located in the camshaft cover of each cylinder bank. Each ignition module assembly contains an ignition control module and 4 ignition coils. Each ignition coil connects directly to a spark plug using a boot. This arrangement eliminates the need for secondary ignition wires. The ignition module assemblies receive power from a fused ignition feed. Both ignition module assemblies connect to chassis ground. A reference low and 4 ignition control (IC) circuits connect each ignition module assembly to the PCM. The PCM uses the individual IC circuits in order to control coil sequencing and spark timing for each ignition coil. The IC circuits transmit timing pulses from the PCM to the ignition control module to trigger the ignition coil and fire the spark plug. The PCM monitors each IC circuit for improper voltage levels. If a short to ground occurs in the IC circuit, this DTC will set.

Conditions for Running the DTC

The engine speed is more than 400 RPM.

Conditions for Setting the DTC

The PCM detects a short to ground on the IC circuit for less than 1 second.

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.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Start and idle the engine.
  2. Monitor the scan tool misfire counters.

Do the scan tool misfire counters increment for the suspect cylinder?

Go to Step 3

Go to Intermittent Conditions

3

  1. Turn OFF the ignition.
  2. Disconnect the ignition coil cassette connector associated with the affected cylinder.
  3. Probe the affected IC circuit in the harness connector with a test lamp connected to battery positive voltage.

Does the test lamp illuminate?

Go to Step 4

Go to Step 6

4

  1. Leave test lamp connected.
  2. Disconnect the PCM connector.

Does the test lamp illuminate?

Go to Step 5

Go to Step 7

5

Repair the short to ground in the affected Cylinder IC circuit. Refer to Wiring Repairs Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 8

--

6

Replace the ICM. Refer to Ignition Coil Replacement - Bank 1 or Ignition Coil Replacement - Bank 2 .

Did you complete the replacement?

Go to Step 8

--

7

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 8

--

8

  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 9

Go to Step 2

9

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK