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Home >> Volkswagen >> 1989 >> Jetta L4-1781cc 1.8L DOHC (PL) >> Repair and Diagnosis >> Relays and Modules >> Relays and Modules - Powertrain Management >> Relays and Modules - Computers and Control Systems >> Knock Sensor Module >> Testing and Inspection >> System Test

System Test


CONTROL UNIT TEST

NOTE: Ignition coil, and Hall control unit must be OK.

Knock Control Unit Harness Connector:





1. Remove the harness connector from the knock sensor control unit.
2. With a suitable volt/ohm meter measure between terminals 3 and 5 of the control unit harness connector.

^ The correct measurement should be approx. battery voltage.

If the correct measurement is not obtained check the power supply and ground to the knock control unit. Refer to CHASSIS ELECTRICAL DIAGRAMS.

3. With the throttle valve closed, measure between terminals 6 and 3.

^ The correct measurement should be approx. battery voltage.

4. Open the throttle valve.

^ The correct measurement should be 0 volts.

If the correct measurements are not obtained check the operation of the throttle switch idle contact. Refer to COMPONENT TESTING.

5. Measure the voltage between terminals 8 and 3 while slowly opening the throttle valve fully.

^ The correct measurement at wide open throttle should be approx. battery voltage.

If the correct measurement is not obtained check the operation of the full throttle switch contact. Refer to COMPONENT TESTING.

6. With the ignition "OFF", reconnect the knock control unit harness connector.

Knock Control System Testing:





7. Remove the harness connector from the Hall sender at the ignition distributor.
8. Turn the ignition switch "ON".
9. Measure the voltage between the two outer terminals of the Hall sender harness connector.

^ The correct measurement should be 5 volts minimum.

10. Switch the ignition "OFF".

Knock Control System Testing:





11. Connect the volt meter between terminal 1 and 15 of the ignition coil.
12. Switch "ON" the ignition.
13. Briefly connect the center terminal of the harness connector from the Hall sender to ground.

^ The voltage must increase briefly to 2 volts minimum.

If the correct results are not obtained replace the knock sensor control unit.

14. With the ignition "OFF", reconnect all harness connectors.

KNOCK SENSOR TESTING

Knock Sensor:





NOTE: Complaints of poor performance at low RPM's, and/or ignition ping at approx. 3000 RPM and above, may be caused by an incorrectly torqued knock sensor mounting bolt. Knock sensor torque (15 - 18 ft. lbs.).

1. With the ignition "OFF", remove the harness connector from the knock control unit.
2. Measure the resistance between terminals 13 and 14 of the harness connector.

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

If the correct measurement is not obtained check the harness for shorts. If the harness is OK, replace the knock sensor.

3. Reinstall the knock control unit harness connector.

FAULT RECOGNITION TEST

Knock Control Testing:





1. Connect the LED test light between terminal #1 (test terminal), which is located on the harness leading to the ignition distributor, and the positive battery terminal.

CAUTION: Damage will result if terminal #1 is connected directly to the positive battery terminal.


2. Turn the ignition "ON".

^ The LED test light should illuminate indicating that the knock control unit is responding. If the LED does not illuminate, check the circuit to terminal #4 of the knock control unit. If the circuit is OK the control unit may be bad. Refer to CHASSIS ELECTRICAL DIAGRAMS.

3. Start the engine and accelerate to above 3000 RPM briefly.

^ The LED should go out, indicating that the system is operating correctly and there are no faults stored. If the LED does not go out, or it goes out and comes back on, a fault has been recognized.

4. If a fault has been recognized, let the engine continue to idle and keep the LED test light in place.
5. Connect a jumper wire from the test connector #1 to ground for at least 3 seconds. The LED test light should flash in coded intervals.

^ Two flashes per interval indicates a fault with the knock sensor wiring, the knock sensor, or the knock sensor control unit.
^ Three flashes per interval indicates a fault with the vacuum connection to the knock sensor control unit or the vacuum signal circuitry of the control unit itself.

NOTE: If the LED does not flash the knock control unit is defective and should be replaced. The fault memory will be erased if the ignition switch is turned "OFF" during this test.

ERASING FAULT CODES

6. Fault codes will be erased after the ignition is switched "OFF", and the engine restarted.


Self Constructed Led Test Light:





If a LED test light is not available, make your own from items purchased from your local electronics store.
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