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Electrical Load Signal: G20

  1. Turn ignition on. Measure voltage between ground and ECM terminal No. 50 by backprobing. See Figure and Figure . With rear window defogger switch in ON position, battery voltage should exist. With rear window defogger switch in OFF position, zero volts should exist. If voltage is as specified, go to next step. If voltage is not as specified, go to step  3.
  2. While monitoring voltage, turn headlight switch to ON position. Battery voltage should exist. Turn headlight switch to OFF position. Zero volts should exist. If voltage is as specified, system is okay. If voltage is not as specified, go to step  6.
  3. Start engine. Turn rear window defogger on. If rear window heats up, go to next step. If rear window does not heat up, repair rear window defogger system. See REAR WINDOW DEFOGGERS article in ACCESSORIES & EQUIPMENT.
  4. Turn ignition off. Disconnect ECM harness connector. Disconnect rear window defogger relay harness connector located in engine compartment relay box. Connect negative ohmmeter lead to rear window defogger relay harness connector terminal No. 5 (Blue/Red wire). Connect positive ohmmeter lead to ECM harness connector terminal No. 50 (Red wire). Continuity should exist. Reverse ohmmeter leads. Continuity should not exist. If continuity is as specified, go to step  9. If continuity is not as specified, go to next step.
  5. Check for open or short in the following wires:
    • Blue/Red wire between rear window defogger relay harness connector terminal No. 5 and connector M-93 terminal No. 3.
    • White wire between connector M-93 terminal No. 4 and connector M-94 terminal No. 3.
    • Red wire between ECM harness connector terminal No. 50 and connector M-94 terminal No. 4.

    Connectors M-93 and M-94 are located behind top of instrument panel, near center of vehicle, taped to main wiring harness. See appropriate wiring diagram in REAR WINDOW DEFOGGERS article in ACCESSORIES & EQUIPMENT. Also check diodes located at connectors M-93 and M-94. Repair as necessary and retest system. If circuits and diodes are okay, go to step  9.

  6. Start engine. Turn headlights on. If headlights operate, go to next step. If headlights do not operate, repair headlights and retest system. See appropriate wiring diagram in HEADLIGHT SYSTEMS article in ACCESSORIES & EQUIPMENT.
  7. Turn ignition off. Disconnect ECM harness connector. Disconnect headlight switch harness connector. Connect positive ohmmeter lead to ECM harness connector terminal No. 50. Connect negative ohmmeter lead to headlight switch harness connector terminal No. 9 (Red/Black wire), then terminal No. 10 (Red/Yellow wire). Continuity should exist. Reverse ohmmeter leads. Continuity should not exist. If continuity is as specified, go to step  9. If continuity is not as specified, go to next step.
  8. Check for open or short in the following wires:
    • Red/Yellow wire between headlight switch harness connector terminal No. 10 and connector M-94 terminal No. 1.
    • Red/Black wire between headlight switch harness connector terminal No. 9 and connector M-94 terminal No. 6.
    • Red wire between ECM harness connector terminal No. 50 and connector M-94 terminal No. 4.

    Connector M-94 is located behind top of instrument panel, near center of vehicle, taped to main wiring harness. See appropriate wiring diagram in HEADLIGHT SYSTEMS article in ACCESSORIES & EQUIPMENT. Also check diodes located at connector M-94. Repair as necessary and retest system. If circuits and diodes are okay, go to next step.

  9. No problem is indicated at this time. Problem may be intermittent. See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article.
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