GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Geo 🢒 1997 🢒 Prizm 🢒 DTC 🢒 DTC P0325 Knock Sensor (KS) Circuit

Schematic Reference: Refer to Engine Controls Schematics

Circuit Description

The knock sensor (KS) is used to detect engine detonation. The KS is constructed of a piezoelectric element which generates an AC signal. When engine knock is present, the KS signals the PCM to retard ignition timing. By reducing the ignition timing, the engine detonation should no loner be detected.

Conditions for Setting the DTC

The engine speed in 1 200 RPM or greater, and no KS signal is detected.

Action Taken When the DTC Sets
    • The PCM illuminates the MIL during the second key cycle in which the DTC sets.
    • The PCM will store the conditions which were present when the DTC set as Freeze Frame Data.
    • The PCM will default to maximum spark retard.

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
    • The DTC clears after 40 consecutive warm-up cycles have occurred without a fault.
    • A DTC can be cleared by using the scan tool Clear DTC Information function.

Diagnostic Aids
    • This information included in the Freeze Frame data can be used in determining the vehicle operating conditions when the DTC first set.
    • An intermittent malfunction may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside the insulation. Inspect harness connectors for backed out terminals, improper matting, broken locks, terminal-to-wire connection before component replacement.
    • Check and correct any abnormal engine noise before using the diagnostic table.
    • Check that the KS is not loose.
    • Fuel type (octane).

Test Description

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

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

    2.

  2. This step checks whether the DTC P0325 is the result of a hard failure or an intermittent condition.

  3. This step checks whether the fault is caused by mechanical failure.

    4.

  4. Checking the internal resistance of the knock sensor verifies if the knock sensor or the wiring to the knock sensor is OK.

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Clear the DTC.
  2. Using the scan tool, place the vehicle into Check Mode.
  3. Operate the vehicle within the Freeze Frame conditions as noted.

Does DTC P0325 set?

--

Go to Step 3

Go to Diagnostic Aids

3

Check the following conditions:

    • Ignition timing
    • EGR operation
    • Correct octane and uncontaminated fuel
    • Mechanical engine noise

Was a problem found.

--

Go to Step 8

Go to Step 4

4

  1. Turn the ignition switch OFF.
  2. Disconnect the PCM electrical connector
  3. Using DMM, connect the DMM to the KS input circuit at the PCM harness connector and to ground.
  4. With the DMM connected to the KS input and ground measure resistance.

Does the DMM read the specified value or greater?

1M ohms

Go to Step 6

Go to Step 5

5
  1. Disconnect the KS connector.
  2. Using a DMM, connect the DMM to the KS terminal connector (KS side) and to ground.
  3. With the DMM connected to the KS terminal and ground, measure resistance.

Does the DMM read the specified value or greater?

1M ohms

Go to Step 6

Go to Step 7

6
  1. Check for an or short in KS input circuit.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 10

Go to Step 7

7

Inspect the KS sensor electrical connections at the KS sensor and the PCM. If the KS sensor connection is OK, then replace the Knock Sensor.

Is the Knock Sensor condition gone?

--

Go to Step 10

Go to Step 9

8

Repair the base engine problem.

Is the action complete?

--

Go to Step 10

--

9

Replace the PCM. Refer to Powertrain Control Module Replacement.

Is the action complete?

--

Go to Step 10

--

10
  1. After repairs, use the scan tool clear information function and road test the vehicle with the Freeze Frame conditions that set the DTC.
  2. Check for DTCs.
  3. Review the scan tool data and if not DTCs are stored repair is complete.

Are any DTCs displayed on the scan tool?

--

Go to the applicable DTC table

System OK