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Home >> Chevrolet >> 1996 >> Corvette Base, 2D Convertible, 5.7 5 >> Repair and Diagnosis >> Body & Frame >> Body, Cab Control Systems >> Central Control Module >> Diagnosing & Repairing CCM DTCS >> DTC 74, Led Display Dimming Output CKT Open Or SHRTED To GRND >> Testing
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DTC 74, Led Display Dimming Output CKT Open Or SHRTED To GRND: Testing

  1. Cover ambient light sensor on Driver Information Center (DIC) with dark tape to simulate darkness. Turn parking lights on and operate dimmer control. If instrument panel and cluster lighting does not dim and brighten with dimmer control, repair dimmer control. Go to next step after repairs. If instrument panel and cluster lighting dims and brightens with dimmer control, go to next step.
  2. Turn parking lights on. Place dimmer control in middle of adjustment position. Turn ignition switch to OFF position. Remove radio control head leaving connector connected. Using a test light, backprobe radio control head harness connector terminal No. 2 to battery voltage. Turn ignition switch to ON position. If test light illuminates, go to step 4) If test light does not illuminate, go to next step.
  3. Check for open in LED dim control circuit between CCM and splice where circuit branches off to individual components. Repair circuit as necessary. If circuit is okay, check for intermittents. Clear DTCs and operate dimmer control. If DTC 74 sets, replace CCM.
  4. Operate dimmer control. If test light brightness changes as dimmer control is operated, clear DTCs and operate dimmer control. If DTC 74 sets, replace CCM.
  5. Disconnect radio control head connector. Using adapter from Terminal Test Adapter Kit (J 35616-A), connect a test light between radio control head harness connector terminal No. 2 and battery voltage. Operate dimmer control and observe test light. If test light brightness changes as dimmer control is operated, replace radio control head. If test light brightness does not change as dimmer control is operated, go to next step.
  6. Remove headlight switch assembly. Disconnect headlight switch 4-pin connector C2. Operate dimmer control and observe test light. If test light brightness changes as dimmer control is operated, replace headlight switch assembly. If test light brightness does not change as dimmer control is operated, go to next step.
  7. Remove heater/air conditioning control head. Disconnect heater/air conditioning control head connector. Operate dimmer control and observe test light. If test light brightness changes as dimmer control is operated, replace heater/air conditioning control head. If test light brightness does not change as dimmer control is operated, go to next step.
  8. Disconnect CCM Gray connector. If test light illuminates, repair short to ground in LED dim control circuit. If test light does not illuminate, reconnect CCM Gray connector. Clear DTCs and operate dimmer control. If DTC 74 sets, replace CCM.
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