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Home >> Jeep >> 2000 >> Grand Cherokee Laredo, 4.0 S, AWD >> Repair and Diagnosis >> Body & Frame >> Body, Cab Control Systems >> Body Control Modules >> System Tests >> Electrically Heated Systems >> Rear Defogger Relay Open
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Rear Defogger Relay Open

  1. Remove and inspect fuse No. 2 (40-amp) from Power Distribution Center (PDC) located in engine compartment. See Figure. If fuse is blown, go to next step. If fuse is okay, go to step  4.
  2. Access junction block on left side of instrument panel. See Figure. Remove rear window defogger relay. Using DVOM, measure resistance between rear window defogger relay cavities No. 30 and 85 and ground. See Figure. If resistance is greater than 5 ohms, go to next step. If resistance is less than 5 ohms, repair short to ground in fused B+ circuit between junction block and PDC and replace fuse. Perform BODY VERIFICATION TEST  under VERIFICATION TESTS.
  3. Disconnect rear window defogger connector at rear window grid. Using DVOM, measure resistance between ground and rear window defogger connector terminal (Black/White wire). If resistance is greater than 5 ohms, replace faulty fuse No. 2. Perform BODY VERIFICATION TEST  under VERIFICATION TESTS. If resistance is less than 5 ohms, repair short to ground in Black/White wire between junction block and rear window defogger grid. Perform BODY VERIFICATION TEST  under VERIFICATION TESTS.
  4. Access junction block on left side of instrument panel. See Figure. Remove rear window defogger relay. Using DVOM, measure voltage between rear window defogger relay cavities No. 30 and 85 and ground. See Figure. If voltage is greater than 10 volts, go to next step. If voltage is less than 10 volts, repair open in fused B+ circuit between junction block and PDC. Perform BODY VERIFICATION TEST  under VERIFICATION TESTS.
  5. Connect test light between rear window defogger relay cavities No. 85 and 86 in junction block. See Figure. Using scan tool, activate R DEFOG RELAY on and off. If test light does not react to scan tool activation, go to next step. If test light flashes on and off, replace rear defogger relay. Perform BODY VERIFICATION TEST  under VERIFICATION TESTS.
  6. Turn ignition off. Disconnect Body Control Module (BCM) from junction block. See Figure. Turn ignition on. Using DVOM, measure resistance between rear window defogger relay socket No. 86 and ground. If resistance is greater than 1000 ohms, go to next step. If resistance is less than 1000 ohms, replace junction block. Perform BODY VERIFICATION TEST  under VERIFICATION TESTS.
  7. Using DVOM, measure resistance between BCM junction block connector terminal No. 11 and rear window defogger relay socket No. 86. See Figure. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, replace junction block. Perform BODY VERIFICATION TEST  under VERIFICATION TESTS.
  8. Replace BCM. See BODY CONTROL MODULE  under REMOVAL & INSTALLATION. Perform BODY VERIFICATION TEST  under VERIFICATION TESTS.
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