With Scan Tool

The heater and A/C programmer contains sophisticated self diagnostics that, when accessed with a scan tool, are designed to identify the source of any system malfunction as specifically as possible, including whether or not the malfunction is current or the noncurrent (history) type. when a fault is present the VF display panel will flash.

There are 11 HVAC diagnostic trouble codes to assist with diagnosis.

The only way to display diagnostic trouble codes (DTCs) is by using a scan tool. There are no provisions for ON-BOARD diagnostics.