For 1990-2009 cars

### Circuit Description

The knock sensor (KS) produces an AC Voltage at all engine speeds and loads. The powertrain control module (PCM) then adjusts the spark timing based on the amplitude and frequency of the KS signal. The PCM uses the KS signal in order to calculate the average voltage. Then the PCM assigns a voltage value. The PCM checks the KS and related wiring by comparing the actual knock signal to the assigned voltage range. A normal KS signal should stay within the assigned voltage range. This diagnostic trouble code (DTC) will set if the KS signal is outside the assigned voltage range or if the signal is not present.

### Conditions for Running the DTC

• | DTCs P0122 or P0123 are not set.

• | The engine coolant temperature (ECT) is more than 70°C (140°F).

• | The engine run time is more than 20 seconds.

• | The manifold absolute pressure (MAP) is more than 60 kPa (8.70 psi).

• | The engine speed is between 1,800-6,400 RPM.

### Conditions for Setting the DTC

The KS is outside the assigned range, or the KS is not present.

### 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.

### Diagnostic Aids

• | The knock sensor must be torqued correctly to 25 N·m (19 lb ft).

• | The mounting between the sensor and engine must be free of burrs, casting flash, and foreign material.

• | The knock sensor head is clear from hoses, brackets, and engine wiring.

• | If an intermittent is suspected, refer to Intermittent Conditions .

### Test Description

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

1. This step ensures the malfunction is present.

2. This step ensures that the knock sensor is capable of detecting detonation and producing a signal.

3. If the KS signal wire is shorted to ground or shorted to voltage the knock sensor may still produce a signal.

4. If the KS signal low reference is shorted to ground or shorted to voltage the knock sensor may still produce a signal.

Step | Action | 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 | Important: If an engine knock can be heard, repair the engine mechanical condition before proceeding with this diagnostic.

1. Observe the Freeze Frame/Failure Records data 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/Failure Records data that you observed.

Does the DTC fail this ignition?

Go to Step 3

Go to Intermittent Conditions

3 |

1. Turn ON the ignition with the engine OFF.
2. Use the scan tool in order to save the Freeze Frame/Failure Records data stored when the DTC set.
3. Turn OFF the ignition and wait 30 seconds.
4. Disconnect the PCM connector.
5. With the DMM set to the 400 mV AC hertz scale, observe the frequency between the KS signal and the KS low reference while tapping on the block with a non-metallic object. Refer to Measuring Frequency in Wiring Systems.

Does the DMM display a fluctuating frequency while tapping on the block?

Go to Step 6

Go to Step 4

4 |

1. Disconnect the knock sensor pigtail connector.
2. Test for an open in the knock sensor signal or low reference circuits. Refer to Testing for Continuity in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 5

5 | Inspect for a poor connection at the knock sensor pigtail harness connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 9
6 | Test for a short to ground or a short to voltage in the KS signal circuit. Refer to Testing for Short to Ground and Testing for a Short to Voltage in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 7
7 | Test for a short to ground or short to voltage in the KS low reference circuit. Refer to Testing for Short to Ground and Testing for a Short to Voltage in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 8
8 | Inspect for a poor connection at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 10
9 | Replace the knock sensor. Refer to Knock Sensor Replacement . Did you complete the replacement? | Go to Step 12 | --
10 | Inspect the knock sensor and harness pigtail assembly for damage. Did you find and correct the condition? | Go to Step 12 | Go to Step 11
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | Go to Step 12 | --
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 | System OK