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For 1990-2009 cars only

Circuit Description

The DTC P0325 Knock Sensor (KS) Circuit diagnostic monitors the activity on the knock sensor circuit. The KS is non-resonant design that is constructed of a piezoelectric element which generates an AC signal, when vibrated. Normal engine operation will cause the KS to generate signals of known frequencies. When engine knock is present, the KS frequency changes. This signals the powertrain control module (PCM) to retard ignition timing. The PCM sends a bias voltage of 5 volts to the KS on the KS Signal High circuit. The PCM expects approximately 2.5 volts back on the KS Signal Low circuit. The KS generated AC signal rides on top of the bias voltage provided by the PCM. For additional information on the operation of the KS refer to Knock Sensor (KS) System Description .

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0325 Knock Sensor (KS) Circuit

Conditions for Running the DTC

    • First condition--The engine is running
    • Second condition--The vehicle speed sensor (VSS) and the throttle position (TP) sensor indicate that the vehicle is accelerating with the engine speed more than 2,000 RPM
    • DTC P0325 runs continuously once the above conditions have been met.

Conditions for Setting the DTC

    • First condition--The KS signal circuit is less than 0.5 volts for at least 10 seconds.
    • Second condition--The KS signal circuit is more than 4.5 volts for at least 10 seconds.

Action Taken When the DTC Sets

    • The PCM illuminates the malfunction indicator lamp (MIL).
    • The PCM stores the conditions that were present when the DTC set as Freeze Frame data.
    • The PCM enters the Fail-Safe function and defaults to maximum spark retard values.

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

Inspect for the following conditions:

    • A loose KS can cause a loss of the KS signal. Check the KS for proper torque. The correct KS sensor torque is 39 N·m (29 lb ft).
    • Engine acceleration will be compromised and automatic transmission (AT) downshifts delayed when operating in the Fail-safe mode.
    • If a DTC P0325 sets while the engine is idling, inspect for a loose connection at the PCM or KS.

An intermittent malfunction may be caused by a fault in the KS sensor electrical circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .

The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions present when the DTC first set.

Test Description

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

  1. The Diagnostic System Check - Vehicle 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. This step verifies whether the DTC P0325 is the result of a hard failure or an intermittent condition. Operating the vehicle in Check Mode enhances the diagnostic capabilities of the PCM.

  3. This step verifies the resistance of the KS.

  4. This step verifies the knock sensors ability to output the correct frequency signal for a given engine speed.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Turn OFF the ignition.
  2. Disconnect the knock sensor (KS) electrical connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage across the KS connector, harness side, with a DMM.

Is the voltage near the specified value?

5 V

Go to Step 4

Go to Step 3

3

Measure the voltage from the KS Signal High circuit to a good ground with the DMM.

Is the voltage near the specified value?

5 V

Go to Step 7

Go to Step 6

4

  1. Turn OFF the ignition.
  2. Connect the KS electrical connector.
  3. Disconnect the powertrain control module (PCM) electrical connector C2.
  4. Measure the resistance between the KS Signal High circuit and the KS Signal Low circuit with the DMM.

Is the resistance near the specified value?

200k ohms at 20°C (68°F)

Go to Step 5

Go to Step 8

5

  1. Turn OFF the ignition.
  2. Reconnect the C2 PCM connector.
  3. Backprobe between the KS Signal High circuit and the KS Signal Low circuit with the DMM.
  4. Select AC voltage and set to indicate Hz.
  5. Start the engine.
  6. Observe that the Hz frequency at idle is within the first specified value.
  7. Operate the engine at 4,000 RPM while observing that the Hz frequency increased to more than the second specified value.

Was the Hz frequency observed during both tests within the specified values?

0.5-2 kHz

21-29 kHz

Go to Diagnostic Aids

Go to Step 8

6

  1. Inspect for an open or a short in the KS Signal High circuit.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and repair a condition?

--

Go to Step 12

Go to Step 10

7

  1. Inspect for an open in the KS Signal Low circuit.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and repair a condition?

--

Go to Step 12

Go to Step 10

8

  1. Inspect for a poor connection at the KS. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and repair a condition?

--

Go to Step 12

Go to Step 9

9

Replace the knock sensor. Refer to Knock Sensor Replacement .

Did you complete the replacement?

--

Go to Step 12

--

10

  1. Inspect for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and repair a condition?

--

Go to Step 12

Go to Step 11

11

Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 12

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12

  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 13

Go to Step 2

13

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 - Vehicle in Vehicle DTC Information

System OK