GM Service Manual Online
For 1990-2009 cars only

Object Number: 33289  Size: SF
Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The VCM uses the Knock Sensors in order to detect engine detonation. This detection allows the VCM to retard the Ignition Control (IC) spark timing based on the KS signal the VCM receives. The circuitry within the knock sensor pulls down the VCM-supplied 5 volt signal, so that under a no knock condition the signal on the KS circuit measures about 1.3 volts. The knock sensors produce an AC signal that rides on the 1.3 volts DC. The signal amplitude and frequency are dependent upon the amount of the knock being experienced.

The VCM contains a replaceable Knock Sensor (KS) module. The KS module contains the circuitry that allows the VCM to utilize the KS signal and to diagnose the KS sensors and circuitry. If the KS module is missing or faulty which causes a continuous knock condition, the VCM sets this DTC.

Conditions for Setting the DTC

    • The DTC P0327 is not active
    • Engine run time is at least 120 seconds.
    • System voltage is greater than 10 volts but is no more than 17.1 volts.
    • The VCM detects a problem with the KS module circuitry that causes the knock to be indicated continuously
    • The above conditions met for up to 0.5 second

Action Taken When DTC Sets

    • The VCM will not illuminate the MIL
    • The VCM will store the conditions which were present when the DTC set as a Fail Records data only. This information will not store as Freeze Frame Data.
    • The VCM will use a calculated spark retard value in order to minimize the knock during the conditions when the knock is most likely to occur. The calculated value will vary based on the engine speed and load.

Conditions for Clearing the MIL/DTC

    • A history DTC will clear after 40 consecutive warm-up cycles have occurred without a fault
    • The scan tool Clear Info function or disconnecting the VCM battery feed can clear the DTC

Diagnostic Aids

Check for the following conditions:

    • A poor connection at the VCM. Inspect the KS module connector for the following conditions:
       - Backed out terminals
       - Broken locks
       - Improperly formed or damaged terminals
    • A damaged or improperly installed KS module. Check for the following items:
       - Bent pins
       - Deformed terminals
       - KS module not completely seated
    • Improper Knock Sensor torque specification. Torque the Knock sensor to 19 N·m (14 lb ft). Refer to

Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

.

Review the Fail Records vehicle mileage since the diagnostic test last failed in order to help determine how often the conditions that caused the DTC to set occur. This may assist in diagnosing the condition.

Test Description

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

  1. This step ensures that the fault is present.

  2. This step checks for an improperly installed KS module

Step

Action

Value(s)

Yes

No

1

Important: Before clearing the DTCs, use the scan tool to record freeze frame and failure records for reference because data will be lost when the Clear Info function is used.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Important: If you can hear the engine knock, repair the engine mechanical problem before proceeding with this diagnostic.

  1. Operate the engine within the conditions specified in the diagnostic support text Conditions for Setting the DTC.
  2. Using a scan tool, monitor the Specific DTC info for the DTC P0325 until the DTC P0325 test runds.
  3. Observe the test results.

Does the scan tool indicate the DTC P0325 Failed This Ign?

--

Go to Step 4

Go to Step 3

3

  1. Turn ON the ignition leaving the engine off.
  2. Review the scan tool Fail Records data for DTC P0325.
  3. Record the scan tool Fail Records data for DTC P0325.
  4. Operate the vehicle within the Fail Records coditions.
  5. Using a scan tool, monitor the SPECIFIC DTC info for DTCP0325 test runs.

Does the scan tool indicate DTC P0325 test Failed This Ign?

--

Go to Step 4

Refer to The Diagnostic Aids

4

  1. Check the KS signal circuit for incorrect routing near the secondary wires.
  2. If a problem, repair as necessary.

Was a problem found

--

Go to Step 8

Go to Step 5

5

  1. Check the KS signal circuit for not being fully seated or for correct installation.
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 8

Go to Step 6

6

  1. Replace the KS module.
  2. Operate the engine within the conditions specified in the diagnostic supporting text Conditions for Setting the DTC.
  3. Using a scan tool, monitor the Specific DTC info for DTC P0325 until the DTC P0325 test runs.
  4. Observe the test results.

Does the scan tool indicate the DTC P0325 Failed This Ign?

--

Go to Step 7

Go to Step 8

7

Replace the VCM.

Important: If the VCM is faulty, the new VCM must be programmed.

Refer to VCM Replacement/Programming .

Is the repair complete?

--

Go to Step 8

--

8

  1. Using the scan tool, select DTC, Clear Info.
  2. Start engine and idle at normal operating temperature.
  3. Select DTC and Specific.
  4. Enter the DTC number which was set.
  5. Operate vehicle within the conditions for setting this DTC as specified in the supporting text.

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

--

Go to Step 9

Go to Step 2

9

Using the scan tool, select Capture Info and Review Info.

Are any DTCs displayed that have not been diagnosed?

--

Go to The Applicable DTC Table

System OK