DTC 2142

1. With the ignition "OFF", disconnect the Motronic control unit harness connector. The Motronic control unit is located beneath the drip tray, at the left rear (drivers side) of the engine compartment.
2. Connect a suitable volt/ohm meter between terminal 24 and 8 of the Motronic control unit harness connector. Set the volt/ohm meter to ohms.

Special Tools:

CAUTION: Avoid damaging the delicate connectors within the control unit harness connector. A simple set of test leads can be fabricated using flat connectors (part # VW N 17 457 2) or equivalent, and a pair of alligator clips.

Knock Sensor Location:

3. Disconnect knock sensor I (right side of engine) harness connector, which is located near the oil filter.

^ The correct measurement should be infinite ohms (no continuity).

If continuity exists the knock sensor harness is shorted. Repair or replace as necessary.

Terminal Identification:

4. Bridge terminals 1 and 2 of the knock sensor harness connector.

^ The correct measurement should be 0.5 ohms or less (continuity).

If continuity is not present the knock sensor harness is open. Repair or replace as necessary. If all measurements are correct, remove the bridge and continue with step 5.

5. Check that the knock sensor mounting bolt torque is within specification (engine cold, 15 - 18 ft. lbs.). CAREFULLY, loosen and retorque as necessary.

WARNING: Disconnect the battery ground strap. Limited space between the alternator electrical connection and the knock sensor mounting bolt may cause an accidental short between the two components.

6. Check for proper cable routing, refer to CHASSIS ELECTRICAL DIAGRAMS.
7. Verify that the terminals for the knock sensor harness connectors are of the same material. Replacement knock sensors have gold plated terminals. Earlier original equipment sensors have alloy plated terminals. If a knock sensor with gold terminals is installed, be sure to replace the matching harness connector with gold terminals.
8. With the ignition "OFF", reconnect the Motronic control unit harness connector to the control unit.

OSCILLOSC0PE TEST

9. Connect the pick-up lead of a suitable oscilloscope to terminal #2 of the knock sensor.

NOTE: Refer to manufactures instructions for the test equipment used.

10. Start the engine and warm to operating temperature.

Oscilloscope Display:

11. Operate the engine at 5000 rpm and observe the scope pattern. Refer to the oscilloscope display.

^ If the pattern does not appear similar to the example, the knock sensor or the knock sensor wiring is defective. Repair or replace as necessary.
^ If the pattern is similar to the example, the knock sensor is OK. The CIS-E Motronic control unit may be defective.

*** UPDATED BY TSB # 289003