Valuable information here for those with a digital dual climate control unit in their Grand Prix. I had printed this off back in 1998 and put it away in a safe place...just now found it. (Talk about a VERY safe place) These are some cool things you can program your display to do, and there are trouble codes to help trouble shoot the problem. GM doesn't even know about these or this feature, this came from the company who built these units for GM. Some how somebody got ahold of them years back worth a copy and paste maybe even a print for your own records. I will type it word for word below:

Press and hold both the driver and passenger knobs in simultaneously until the display changes to read "-00". To change position, turn the driver knob to the desired number and turn the passenger knob one click to view the data for that position.

Position description US observed on mine Canada:
-00 error codes click here for the trouble codes chart (below - typed last)
-01 (servo position) 103-107 43-162
-02 (servo position) 128 120-202
-03 (servo position) 150 162-194
-04 CJ2 fan speed low=15, 29, 44, 58, 71, 86, 110=high, CJ2 unit will adjust to other increments as needed.
-05 (servo position) 93 88-191
-06 (servo position) -152 00-252
-07 (servo position) 00 0, 34-255
-08 (servo position) -155 00-255
-09 (servo position) 00 0, 23-255
-10 ? 04 04
-11 CJ2 vent mode 1=Def, 2=Bilevel, 3=Auto, 4=Lower, 5=Def+Lower
-12 Engine Coolant Temp -60 degrees 80=104, 95=131, 11=140 Peak@1 35*F
-13 Actual Vehicle Speed in MPH
-14 (servo position) 00 21=0
-15 ? 39 44
-16 Radiator low fan turn on temp -106 207
-17 Radiator low fan turn off temp 196 199
-18 ? 50 51
-19 (servo position) 162-169 40-172
-20 Affected by cabin temp sensor 89 50-172
-21 (servo position) 00 ?
-22 Sunload Sensor -117 LIGHT-126, 218=DARK
to return to normal operation, press the MODE button next to the passenger temperature knob.

This is a list of the trouble codes displayed by the CJ2 unit. A two digit code indicates a current fault while a three digit code indicates a historic fault.

Trouble Code Description:
00 No System Fault
01 or 101 Inside air temperature sensor short
02 or 102 Inside air temperature sensor open
03 or 103 Ambient outside temperature sensor short
04 or 104 Ambient outside temperature sensor open
05 or 105 LH electric actuator open or short
06 or 106 RH electric actuator open or short
07 or 107 UART serial data line fault
08 or 108 solar sensor open

To clear codes from the CJ2 unit, press the A/C Mode button.

~F~