For 1990-2009 cars

### Circuit Description

The DTC P0325 Knock Sensor (KS) Circuit diagnostic monitors the activity on the knock sensor circuit. The KS is used to detect engine detonation. The KS is constructed of a piezoelectric element which generates an AC signal when vibrated. Normal engine operation will cause the KS to generate a signal of a certain known frequency. When engine knock is present, the KS frequency changes which signals the powertrain control module (PCM) to retard ignition timing. By retarding the ignition timing, the engine detonation detected should be reduced.

### Conditions for Running the DTC

• | The engine speed is 1,200 RPM or more.

• | The vehicle speed sensor (VSS) and the throttle position (TP) sensor indicate that the vehicle is accelerating.

### Conditions for Setting the DTC

The KS signal detected is below specifications for more than 20 seconds.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL).

• | The PCM stores the conditions which were present when the DTC set as Freeze Frame data.

• | The PCM enters the Fail-Safe function and defaults 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

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).

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 .

Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.

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-Engine Controls 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 checks 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 checks the knock sensors ability to output the correct frequency signal for a given engine speed.

4. This step checks if the fault is the knock sensor input wiring.

Step | Action | Values | 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. Perform the scan tool Clear DTC Information function.
2. Place the vehicle into Check mode using the scan tool.
3. Operate the vehicle within the Freeze Frame conditions as specified.

Does DTC P0325 set?

--

Go to Step 3

Go to Diagnostic Aids

3 |

1. Turn OFF the ignition.
2. Disconnect the knock sensor connector.
3. Probe the knock sensor terminal on the sensor side with a DMM connected to ground.
4. Select AC frequency and push the Hz button.
5. Start the engine.
6. Operate the engine at 4,000 RPM while monitoring the AC frequency output of the knock sensor.

Is the AC frequency near the specified value?

12.5 kHz

Go to Step 4

Go to Step 6

4 |

1. Turn OFF the ignition.
2. Reconnect the KS connector.
3. Disconnect the PCM connector containing the KS circuit.
4. Remove the KS signal wire terminal from the PCM connector.
5. Connect the PCM electrical connector.
6. Probe the PCM connector KS terminal with the DMM connected to ground.
7. Select AC frequency and push the Hz button.
8. Start the engine.
9. Operate the engine at 4,000 RPM while monitoring the AC frequency output of the KS.

Is the AC frequency near the specified value?

12.5 kHz

Go to Step 7

Go to Step 5

5 |

1. Repair the open or the short in the KS input circuit.
2. Ensure that the terminal connection at the sensor is good.
3. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 8

--

6 | Replace the knock sensor. Refer to Knock Sensor Replacement . Is the action complete? | -- | Go to Step 8 | --
7 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | 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