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Test I: No Communication With Gem/CTM Module

  1. Check fuse No. 25 (7.5-amp) in instrument panel fuse block and maxi-fuse No. 1 (50-amp) in engine compartment fuse block. If fuses are okay, go to next step. If maxi-fuse No. 1 is blown, replace fuse and retest system. If fuse blows again, check for short to ground in Tan/Black wire. Repair as necessary. If fuse No. 25 is blown, replace fuse and retest system. If fuse blows again, check for short to ground in White/Yellow wire. Repair as necessary.
  2. Measure voltage between ground and fuse block connector terminal No. 25 (Tan/Black wire). If voltage is more than 10 volts, go to next step. If voltage is less than 10 volts, repair Tan/Black wire. Clear DTCs and retest system.
  3. Disconnect GEM 18-pin connector C283. Measure voltage between ground and GEM 18-pin connector White/Yellow wire. If voltage is more than 10 volts, go to next step. If voltage is less than 10 volts, repair White/Yellow wire. Clear DTCs and retest system.
  4. Disconnect GEM 26-pin connector C280. Measure resistance between ground and connector C280 Black/White wire terminals No. 14 and 26. See Figure . If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, repair open in Black/White wire(s). Clear DTCs and retest system.
  5. Measure resistance between GEM C283 18-pin connector Black wire terminal No. 18 and ground. If resistance is less than 5 ohms, see MODULE COMMUNICATIONS NETWORK article. If resistance is more than 5 ohms, repair open in Black wire. Clear DTCs and retest system.
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