For 1990-2009 cars
Handling ESD Sensitive Parts Notice
Engine Controls Components
Cell 20: Engine Data Sensors
OBD II Symbol Description Notice

### Circuit Description

The knock sensor (KS) system is used in order to detect any engine detonation. The engine control module (ECM) will retard the spark timing based on the signals from the KS module. The knock sensors produce an AC voltage that is sent to the KS module. 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 an 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 ECT is more than 40°C (104°F).

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

• | 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 mimumum 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

Notice: Using the J 35616-A Connector Test Adapter Kit will prevent damage to the harness connector terminals.

Use the J 35616 connector test adapter kit for any test that requires probing the ECM harness connector or a component harness connector.

Check for the following conditions:

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

• | The KS shield wiring for continuity. Insert a test lamp connected to B+ carefully between the KS wiring outer insulation and the inner wires. Good KS shield continuity will illuminate the test lamp.

• | Poor connections at the ECM or at the component--Inspect the harness connectors for any backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Engine Control Module Diagnosis , Checking Terminal Contact for the proper procedure.

• | Misrouted harness--Inspect the harness in order to ensure that the harness is not routed too close to any high voltage wires, or too close to any high current devices such as the alternator, the motors, the solenoids, etc.

• | Damaged harness--Inspect the wiring harness for any damage. If the harness appears to be OK, observe the scan tool while moving the related connectors and the wiring harnesses. A change in the display may help in order to locate the fault.

| If the sensor signal is only affected when the harness is moved at a component, and there is no problem with the harness or connections, the component may be damaged.

Refer to Symptoms for the Intermittents.

### Test Description

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

1. This test verifies that the malfunction is present.

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.

1. Turn ON the ignition leaving the engine OFF.
2. Review the Freeze Frame data for this DTC and note parameters.
3. Clear the DTCs.
4. Turn OFF the ignition for 15 seconds.
5. Start the engine.
6. Operate the vehicle within the conditions that are required for this diagnostic to run, and as close to the conditions that were recorded in the Freeze Frame as possible. Refer to Conditions for Running the DTC.
7. Check for any DTCs.

Is this DTC set?

--

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. Turn ON the ignition leaving the engine OFF.
4. Use the J 39200 DMM in order to measure the voltage between the knock sensor signal circuit in the ECM harness connector and battery voltage.
5. Use the J 39200 DMM in order to measure the voltage between the knock sensor low circuit in the ECM harness connector and battery voltage.

Is the voltage measured on both circuits greater than the value specified?

10 V

Go to Step 4

Go to Step 7

4 |

1. Turn OFF the ignition.
2. Disconnect the ECM.
3. Use the J 39200 DMM in order to measure the RESISTANCE between the knock sensor signal circuit in the ECM harness connector and ground.
4. Use the J 39200 DMM in order to measure the RESISTANCE between the knock sensor low circuit in the ECM harness connector and ground.
5. Use the J 39200 DMM in order to measure the RESISTANCE between the knock sensor signal and the low circuit in the ECM harness connector.

Is the resistance measured on any test less than the value specified?

2 ohms

Go to Step 8

Go to Step 5

5 |

1. Check for poor connections/terminal tension at the knock sensor connector AND at the ECM connector. Refer to Wiring Repairs in Wiring Systems for the proper procedure. Also, refer to Checking Terminal Contact in Engine Control Module Diagnosis .
2. Repair the connections as necessary.
3. Ensure the knock sensor mounting bolt is tightened to the proper torque.

Did you find and correct a problem?

--

Go to Step 10

Go to Step 6

6 |

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

Did this DTC pass?

--

Go to Step 11

Go to Step 9

7 | Repair the open or high resistance in the circuit that did not indicate voltage higher than the specified value. Is the action complete? | 10 V | Go to Step 10 | --
8 | Repair the circuit that is shorted to ground or repair the KS signal and low circuits shorted together. Is the action complete? | -- | Go to Step 10 | --
9 | 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 10

--

10 |

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 11

Go to Step 2

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