DTC 2141
DTC 2141 (California)*** UPDATED BY TSB # 289003 DATED OCT. 31 1990
1. With the ignition "OFF", disconnect the Digifant control unit harness connector. The Digifant control unit is located at the rear of the engine compartment. For these tests it may be easier to remove the control unit from its mount, this will allow better access to the harness connector pins.
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:
2. Disconnect knock sensor harness connector, which is located near the front of the engine block, near #2 cylinder.
3. Using a suitable digital multimeter set on ohms, measure the resistance between Digifant harness connector pin 29 and Knock sensor harness connector pin 1:
^ The correct measurement should be continuity (1.5 ohms maximum).
4. Measure the resistance between Digifant harness connector pin 27 and Knock sensor harness connector pin 2:
^ The correct measurement should be continuity (1.5 ohms maximum).
5. Measure the resistance between Digifant harness connector pin 8 and Knock sensor harness connector pin 3:
^ The correct measurement should be continuity (1.5 ohms maximum).
If continuity is not present the knock sensor harness is open. Repair or replace as necessary. If all measurements are correct, continue with step 6.
6. Check that the knock sensor mounting bolt torque is within specification, CAREFULLY loosen and retorque to:
^ 15 - 18 ft. lbs. (engine cold)
CAUTION: 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.
7. Check for proper cable routing.
8. 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.
9. With the ignition "OFF", reconnect the Digifant control unit harness connector to the control unit.
OSCILLOSC0PE TEST
1. 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.
2. START the engine and warm to operating temperature.
Oscilloscope Display:
3. 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 Digifant control unit may be defective.