For 1990-2009 cars
Handling ESD Sensitive Parts Notice
Engine Controls Components
Engine Data Sensors
OBD II Symbol Description Notice

### Circuit Description

The knock sensor (KS) system is used in order to detect any engine detonation (spark knock). The engine control module (ECM) will retard the spark timing based on the signals from the KS. The knock sensors produce an AC voltage that is sent to the ECM. The amount of AC voltage produced is proportional to the amount of knock.

An operating engine produces a normal amount of engine mechanical vibration (noise). The knock sensors will produce an AC voltage signal from this noise. When the engine is operating, the ECM will learn the minimum and maximum frequency of the noise the engine produces. When the ECM determines that this frequency is less than or more than the expected amount, a knock sensor diagnostic trouble code (DTC) will set.

### Conditions for Running the DTC

• | The engine coolant temperature (ECT) is more than 40°C (104°F).

• | The engine has idled for 5 seconds allowing the ECM to learn a minimum engine noise level.

• | The engine has been running at least 10 seconds.

• | The engine speed is more than 2,000 RPM.

### Conditions for Setting the DTC

The ECM does not detect a difference between the minimum learned engine noise level at idle and the engine noise between 2500-3500 RPM for 5 seconds.

### Action Taken When the DTC Sets

The ECM will not illuminate the malfunction indicator lamp (MIL).

### Conditions for Clearing the MIL/DTC

• | The DTC clears after forty consecutive warm-up cycles if no failures report by this diagnostic or any other non-emission related diagnostic.

• | The scan tool clears the MIL/DTC.

### Diagnostic Aids

Use the J 35616 connector test adapter kit for any test that requires probing the ECM harness connector or a component harness connector. Using this kit prevents damage to the harness or component terminals. Refer to Using Connector Test Adapters in Wiring Systems. For an intermittent, refer to Symptoms .

Check for the following conditions:

• | The KS shielded wiring for continuity or damage--By rolling back the boot on the KS connector that leads back to the ECM, the shrink wrap will be exposed. Carefully insert a test lamp connected to B+ under the shrink wrap. Good KS shield continuity will illuminate the test lamp.

• | Damaged harness--Inspect the wiring harness for any damage. If the harness appears to be OK, connect the DMM to the signal and reference ground at the ECM connector. Monitor the resistance of the circuit while moving the harness in different locations. A fluctuation in the resistance will indicate the area of a possible concern.

• | Damaged KS lead--If the sensor lead is damaged in any way the sensor must be replaced.

• | Poor connections at the ECM or at the component--Inspect the sensor harness connector and the ECM connections for poor terminal tension or signs of corrosion.

• | Misrouted harness--Inspect the harness in order to ensure that the harness is routed correctly.

• | The knock sensor for proper installation--A knock sensor that is loose or over torqued may cause this DTC to set.

If a repair is necessary refer to Wiring Repairs or Connector Repairs in Wiring Systems.

### Test Description

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

1. This step verifies that the malfunction is present.

2. This test determines if the KS is capable of producing a signal.

3. This test verifies the integrity of the KS signal and reference ground circuits up to the ECM connector.

4. These tests address any faults in the KS signal and reference ground circuits from the ECM to the harness connector for the applicable KS.

5. An improper torque value on the sensor will provide erroneous information to the ECM and a damaged sensor lead requires replacement of the sensor.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Important: If an engine knock can be heard, repair the engine mechanical problem before proceeding with this diagnostic. Refer to Engine Noise Diagnosis in Engine Mechanical.

1. Review the Freeze Frame and/or failure records for this DTC and note the parameters.
2. Clear the DTCs.
3. Turn OFF the ignition for 30 seconds.
4. Start the engine.
5. Operate the vehicle within the conditions for running the DTC as specified in the supporting text and as close to the freeze frame and/or failure records that were noted.
6. Check for any DTCs.

Does this DTC reset?

--

Go to Step 3

Go to Diagnostic Aids

3 |

1. Turn OFF the ignition.
2. Disconnect the knock sensor that applies to this DTC.
3. With the DMM, measure the frequency (Hz) between the KS signal and the KS reference ground circuits at the sensor connector while tapping on the engine lift bracket with a non-metallic object.

Does the DMM display a fluctuating frequency?

--

Go to Step 4

Go to Step 7

4 |

1. Connect the KS sensor connector.
2. Disconnect the ECM.
3. With the DMM, measure the frequency (Hz) between the KS signal and the KS reference ground circuits at the ECM connector while tapping on the engine lift bracket with a non-metallic object.

Does the DMM display a fluctuating frequency?

--

Go to Step 9

Go to Step 5

5 | Test for the following conditions between the ECM connector and the KS harness connector:

• | Open or high resistance in the KS signal and reference ground circuits.

• | Short to voltage on the KS signal circuit.

• | KS signal and reference ground shorted to ground.

• | KS signal and reference ground shorted together.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 6

6 | Test for poor connections or terminal tension at the knock sensor connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 7
7 | Inspect for the KS for proper torque and for a damaged sensor lead. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8
8 | Replace the knock sensor. Refer to Knock Sensor Replacement . Is the action complete? | -- | Go to Step 11 | --
9 | Test for poor connections or terminal tension at the ECM connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10
10 | Important: Perform the Idle Learn Procedure when replacing the ECM or throttle body. Important: This vehicle is equipped with a Theft Deterrent System which interfaces with the Engine Control Module (ECM). Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle.

Replace the ECM. Refer to Engine Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 11

--

11 |

1. Using the scan tool, clear the DTCs.
2. Start the engine.
3. Allow the engine to idle until the engine reaches the normal operating temperature.
4. Select DTC and the Specific DTC function.
5. Enter the DTC number that was set.
6. Operate the vehicle within the Conditions for Running this DTC until the scan tool indicates that the diagnostic Ran.

Does the scan tool indicate that the diagnostic Passed?

--

Go to Step 12

Go to Step 2

12 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK