This is a quick reference for how to use the diagnostic mode built into the dual zone digital climate control system which came installed in some 1997 through 2003 Pontiac Grand Prix Models.
Every time I want to look this up I always have trouble remembering the terms I need to search for to retrieve it, so I have stolen mirrored this from This Forum Post.
To enter diagnostics mode: 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 (List of Trouble Codes Below!) -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, 100=140 Peak@135°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.