System Diagnostics

THIS ARTICLE INCLUDES UPDATES MADE BY TSB #88-422-8A, DATED JULY 1989

DIAGNOSIS
There are 9 diagnostic modes as described below. Diagnostic mode number 8 is the most commonly used mode for diagnosing this system. The diagnostic mode is entered while pressing the rear defrost button and then pressing and releasing the manual up button.

NOTE: Entry into A/C diagnostics requires a Control Assembly with a rear defrost button. A substitute A/C Control Assembly with a rear defrost button may be used temporarily when entry into the A/C diagnostic mode is desired.

Once the diagnostic mode is enabled, the mode number may be changed by pressing the warmer button. The contents of the mode may be displayed by pressing the cooler button. The mode number is displayed preceded by a minus sign.

^ Mode # 1 - Program Number
^ Mode # 2 - In-Car Thermistor
^ Mode # 3 - Ambient Correction
^ Mode # 4 - Blower Number
^ Mode # 5 - Outside Temp Thermistor
^ Mode # 6 - Feedback Pot Position
^ Mode # 7 - Calculated Door Position
^ Mode # 8 - System Faults
^ Mode # 9 - Software Version Number

System Faults - A system fault is indicated by a flashing annunciator. If there is a problem with the Ambient sensor, In-car sensor, or the Feedback potentiometer, the EXT TEMP annunciator will flash for approximately 60 seconds, upon ignition on. The flashing annunciator will reoccur upon ignition on until the system problem has been corrected. To further investigate a system problem, a diagnostic data word can be examined. The diagnostic data word is displayed by entering diagnostic Mode # 8. The diagnostic data word is a number that indicates the failure mode. Faults can be determined by evaluating the Binary Equivalent of the diagnostic data word displayed. A "1" in a column is an indication of an error of that category. The Diagnostic Mode can be exited by depressing any mode button on the ECC control face.