This procedure covers all Bonnevilles from 88-93.

The diagnostic mode also contains a data list mode and an override mode.

Be careful not to select modes 01 or 02, as these are different modes, and may cause problems.

If you believe you are in the wrong mode, then press OFF until you exit to normal mode. If the temperature display flashes for 2 minutes when the ignition is turned to RUN, a trouble code is set.

1) Turn ignition to RUN. Press OFF and WARM (temperature up) buttons at the same time.

2) Watch the segment test, then the trouble codes will be displayed.

3) Match your Code Key below.

00 - No codes

10 or 110 - Ambient Temp Sensor circuit open or shorted.

13 or 113 - In-Vehicle Temp Sensor circuit open or shorted.

15 or 115 - LH Solar Sensor circuit open or shorted.

35 or 135 - Data Line failure - HVAC Control Assembly

38 or 138 - Data Line failure - PCM

40 or 140 - Driver Air Mix Motor circuit open or shorted, or not calibrated

48 or 148 - Long Term Freon Loss

52 or 152 - Keep Alive Memory lost; sets with battery disconnected

66 or 166 - Low Freon

A number 1 prefix indicates a history trouble code

4) Press OFF twice once codes are displayed to end diagnostic mode, OR to clear trouble codes, press FAN DOWN three times (make sure 03 is displayed).

Once 03 is displayed, press FAN UP to clear trouble codes. Then repeatedly press OFF to end diagnostic mode.

NOTE:
If you have the FSM Factory Service Manual for your car there are MANY more diagnostics and procedures you can perform.