A/C-Heater Control Unit Illumination/Display Does Not Operate Properly

WARNING: This page is about a different car, the 2001 Pontiac Bonneville and 2000 Pontiac Bonneville. However, it is still accessible from the selected car via links, so may be relevant.

Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK under TROUBLE SHOOTING and go to next step.
If DTC B2646 in ignition panel module was displayed during diagnostic system test, see appropriate ILLUMINATION/INTERIOR LIGHTS in ACCESSORIES & EQUIPMENT. If DTC B2646 was not displayed, go to next step.
Connect scan tool and turn ignition on. Use scan tool to perform WOW INSTRUMENT CLUSTER COMMAND in INSTRUMENT PANEL CLUSTER SPECIAL FUNCTIONS. If all A/C-heater control unit (A/C-heater control unit) segments come on, go to next step. If all A/C-heater control unit segments do not come on, go to step 7 .
If all other instrument panel Vacuum Fluorescent (VF) displays come on when performing WOW INSTRUMENT CLUSTER command, go to next step. If all other instrument panel VF displays do not come on, see appropriate ILLUMINATION/INTERIOR LIGHTS article in ACCESSORIES & EQUIPMENT.
Cover sunload sensor. Turn on lights. If back lighting works, go to next step. If back lighting does not work, see appropriate ILLUMINATION/INTERIOR LIGHTS article in ACCESSORIES & EQUIPMENT.
Adjust dimmer control from minimum to maximum intensity, If VF display increases and decreases in intensity, system is okay. If VF display does not increase and decrease in intensity, go to next step.
Check for loose wires and poor connections at A/C-heater control unit harness connector. If wiring and connections are okay, go to next step. If wiring and connections are not okay, correct condition and go to step 9 .
Replace A/C-heater control unit. See A/C-HEATER CONTROL UNIT under REMOVAL & INSTALLATION. Go to next step.
Operate system to verify proper operation. If system is not okay, go back to step 2 .