Heating Ventilation Air Conditioning (HVAC)

CIRCUIT DESCRIPTION
The serial data link connects the PCM to the H-A/C control. Data is sent to and received by the PCM to the H-A/C control, ABS system, and the SIR system. The PCM is the "master" of the serial data link.

DTC WILL SET WHEN
With ignition in "RUN," the H-A/C control will set a DTC 26 anytime a fault exists on CKT 800. A short to ground, short to B+ on CKT 800 will set a DTC 26. An open in CKT 800 from 5223 to the H-A/C control will also set a DTC 26.

ACTION TAKEN:
DTC 26 will set in the H-A/C control. If DTC 26 is current, communication can be lost on the serial data link.

DTC WILL CLEAR WHEN
This fault will clear as soon as the fault has been repaired.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test checks for DTC(s) and should clear any intermittent DTC(s).
2. This test checks for "normal" serial data voltage at terminal "M" of the serial data link.
3. This test checks for an open in CKT 800 to the H-A/C control.

DIAGNOSTIC AIDS
Check for an intermittent "open" at terminal "D12" of the H-A/C control connector and/or the corresponding terminal of the H-A/C control. If DTC 26 is current, the H-A/C control will command the A/C compressor clutch to be "ON." If the Tech 1 cannot communicate with the serial data line, refer to Tech 1 "Serial Data Line" diagnosis.

Looking at other systems on CKT 800 (with a scan tool) and returning to the "HVAC" selection can cause a HVAC DTC 26 to set in the H-A/C control. When diagnosing a HVAC DTC 26, clear the DTC and check for HVAC DTCs again.