Knock Sensor - Avoiding Unnecessary Replacement

Group: 28

Number: 93-02

Date: June 15, 1993

Subject:
Avoiding Unnecessary Knock Sensor Replacement

Model(s):
All models with Knock Sensors

Condition

Here are some tips to follow if you suspect that a driveability problem is being caused by the knock sensor system.

Knock sensor malfunction may cause the following symptoms:

^ Vehicle appears to lose power

^ Increased fuel consumption

^ Malfunction Indicator Lamp comes on.

^ VAG 1551 Scan Tool indicates knock sensor malfunction

Knock sensor malfunctions may be caused by:

^ Incorrect or disconnected wiring

^ Corroded terminals (from mismatched terminal material)

^ Knock sensor shielding damaged

^ Improperly torqued knock sensor mounting bolt

^ Abnormal noises caused by

a) torn or loose brackets

b) loose wiring

c) loosened engine components

d) broken, loose or missing bolts

e) mechanical damage

For example, a rhythmic knocking noise from a malfunctioning A/C compressor that increases and decreases with engine RPM could be interpreted by the knock sensor as engine knock.

Service

To avoid making unnecessary repairs, use the following steps when diagnosing suspected knock sensor problems.

- Analyze the problem to determine if it could be knock sensor related.

- Check for abnormal noises caused by:

^ torn or loose brackets

^ loose wiring

^ loosened engine components

^ broken, loose or missing bolts

- Check knock sensor installation torque. Loosen knock sensor bolt and torque to:

^ 20 to 25 N-m (15 to 18 lbs.ft.)

Note

Be sure to use a torque wrench that reads accurately in this range.





- Check that knock sensors (if more than one) are connected to the proper wiring harnesses. (If necessary, refer to Campaign Circular QX)

- Check that the knock sensor wires are not damaged.

- Check knock sensor terminals for correctly matched material. If the knock sensor terminals are tin-plated, the mating connectors must be tin-plated. If the knock sensor terminals are gold-plated, the mating connectors must be gold-plated.

If the terminals are not the same material, metal corrosion has taken place on the terminals and the knock sensor and terminals must be replaced.

- Check that the terminals have been installed in the connector in the proper position using the latest wiring diagram for the vehicle you're working on.

Note

Replacement knock sensors only have gold-plated terminals. Earlier original equipment sensors have alloy plated terminals. Both the make and female terminals of the knock sensor connection must be of the same material.

- Road test the vehicle and check performance

If you still suspect a knock sensor problem,

- Check the fault memory (if possible)

- Check the knock sensor wiring at the ECM

If still no improvement,

- Replace the knock sensor and road test the vehicle again.