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Home >> GMC >> 1998 >> Envoy >> Repair and Diagnosis >> Body & Frame >> Body, Cab Control Systems >> Body Control Module >> Diagnosis & Testing >> DTC B2648: Ambient Light Sensor Circuit High >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform TBC module diagnostic system check. See procedures in TBC MODULE DIAGNOSTIC SYSTEM CHECK  . After performing system check, go to next step.
  2. Install scan tool. Using scan tool, check if DTC B1398 is set as a current code. If code is current, go to step 7). If code is not current, go to next step.
  3. Install scan tool. Turn ignition switch to RUN position. Using scan tool, monitor light sensor voltage. If voltage is 4.78 volts or greater, go to next step. If voltage is not 4.78 volts or greater, problem is intermittent. See DIAGNOSTIC AIDS.
  4. Turn ignition off. Disconnect light sensor connector. Disconnect Purple TBC module harness connector. Check voltage between ground and TBC module harness connector terminals A6 (White wire). If voltage reading is 4.78 volts or greater, go to step 8). If voltage reading is not 4.78 volts or greater, go to next step.
  5. Clear DTCs. Turn ignition off for 10 seconds. Turn ignition switch to RUN position. Check if DTC B2648 is set as a current code. If code is current, go to step 9). If code is not current, go to next step.
  6. Replace light sensor. After replacing sensor, go to step 10).
  7. Perform DTC B1398 diagnostic test procedures. After performing DTC B1398 tests, check if DTC B2648 is set as a current code. If code is current, go to step 3). If code is not current, go to step 10).
  8. Repair short to battery voltage on circuit No. 278 (White wire). After repairs, go to step 10).
  9. Replace TBC module. Program TBC and perform relearn procedure. See procedures in TBC MODULE PROGRAMMING/RPO CONFIGURATION  and TBC/BCM RELEARN PROCEDURE  . After programming module, go to next step.
  10. Clear DTCs. After clearing DTCs, perform TBC module diagnostic system check. See TBC MODULE DIAGNOSTIC SYSTEM CHECK  .
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