GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The powertrain control module (PCM) uses a knock sensor (KS) to detect engine detonation, or spark knock. The knock sensor produces an AC signal at all engine speeds and loads. The PCM makes adjustments to the spark timing based on the amplitude and frequency of the KS signal.

The PCM uses the knock sensor to calculate the amount of normal engine noise (a noise channel) for a wide range of engine speeds and loads. The PCM compares the actual knock sensor signal to the learned noise channel. If the PCM malfunctions in a manner that will not allow proper diagnosis of the KS system, this DTC will set.

Conditions for Running the DTC

    • The engine speed is more than 3000 RPM.
    • The system voltage is greater than 11 volts.

Conditions for Setting the DTC

The PCM detects a malfunction in the integrated KS diagnostic circuitry that will not allow proper diagnosis of the KS system.

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

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step  2

Go to Diagnostic System Check - Engine Controls

2

  1. Observe the Freeze Frame/Failure Record for this DTC.
  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 or as close to the Freeze Frame and/or Failure Records data that you observed.

Does the scan tool indicate that this DTC passed?

Go to Intermittent Conditions

Go to Step 3

3

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

Go to Step 4

--

4

  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 or as close to the Freeze Frame and/or Failure Records data that you observed.

Does the scan tool indicate that this DTC passed?

Go to Step 5

Go to Step 2

5

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