NOTE: In model year 1997, the heater and A/C control unit was manufactured with two different versions of software. With the early version software the scan tool can only read and clear codes. The later version software, the scan tool can read and clear codes, display a data list, and perform special functions (actuator tests.) In addition, several DTC descriptions changed.

The different versions of software will be identified as (Early Software Version) and (Latest Software Version).

A scan tool is a very useful tool and must be used when referred to throughout this section. In addition to displaying DTC(s), the scan tool is capable of displaying input status and data values the heater and A/C control system uses to perform certain functions. It is also capable of sending specific commands to system components to determine if the malfunction is due to the heater and A/C control unit not sending a proper command, or the component that received the command is not responding to the command. Using the actuator test in Special Functions as an example, sending a message to the defroster valve actuator door to cycle from 0% to 100% and to monitor the status (ACTIVE/INACTIVE) can determine if the heater and A/C control can actually perform the function. If the defroster valve actuator is functioning properly and the heater and A/C control unit is still unable to operate the actuator, then the problem is most likely with the control unit.