Rear Mode Control

Models equipped with the optional rear heater-A/C unit have a heat-A/C mode door in the rear heater-A/C unit housing and a rear water valve. The rear heater-A/C mode switching is controlled by a combination of mechanical components and electronic controls. The mechanical components include: the rear heat-A/C mode door, the rear water valve, the rear water valve control cable, and the rear water valve control cable adaptor. The electronic controls include the rear mode control motor and circuits, and a momentary switch and cam mechanism that are driven by the temperature control knob. The switch and cain mechanism are integral to the heater-A/C control on the instrument panel.

The diagnosis found here addresses only the electronic portion of the rear mode control system. If the problem being diagnosed is related to improper rear heat-A/C mode switching, but the rear mode control motor is operational, be certain to check the mechanical components of this system. Inspect the heat-A/C mode door, the rear water valve, the rear water valve control cable, and the rear water valve control cable adaptor for improper installation or damage.

WARNING: ON VEHICLES EQUIPPED WITH AIR-BAGS, REFER TO AIRBAGS BEFORE ATTEMPTING ANY STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENT DIAGNOSIS OR SERVICE. FAILURE TO TAKE THE PROPER PRECAUTIONS COULD RESULT IN ACCIDENTAL AIR-BAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.

1. Check the fuse in the junction block. If OK, go to Step 3. If not OK, repair the shorted circuit or component as required and replace the faulty fuse.
2. Turn the ignition switch to the On position. Check for battery voltage at the fuse in the junction block. If OK, go to Step 4. If not OK, repair the open circuit to the ignition switch as required.
3. Turn the ignition switch to the Off position. Disconnect and isolate the battery negative cable. Remove the heater-A/C control from the instrument panel. See Heater-A/C Control Replacement for the procedures.
4. Check for continuity between the ground circuit cavity of the heater-A/C control Rotary Temperature Mechanism (RTM) wire harness connector and a good ground. There should be continuity If OK, go to Step 6. If not OK, repair the open circuit to ground as required.
5. Check for continuity between the ground circuit terminal and the A/C switch signal terminal in the RTM connector receptacle on the back of the heater-A/C control. There should be continuity with the temperature control knob in the full clockwise (Warm) position, and no continuity with the temperature control knob in the full counterclockwise (Cool) position. If OK, go to Step 7. If not OK, replace the faulty heater-A/C control.
6. Remove the trim cover from the rear heater-A/C unit. See Rear Heater-A/C Cover in the Removal and Installation section of this Replacement for the procedures. Unplug the wire harness connector from the rear mode control motor. Check for continuity between the ground circuit cavity of the rear mode control motor wire harness connector and a good ground. There should be continuity. If OK, go to Step 8. If not OK, repair the open circuit to ground as required.
7. Connect the battery negative cable. Turn the ignition switch to the On position. Check for battery voltage at the fused ignition switch output (run) circuit cavity of the rear mode control motor wire harness connector. If OK, go to Step 9. If not OK, repair the open circuit to the fuse in the junction block as required.
8. Turn the ignition switch to the Off position. Disconnect and isolate the battery negative cable. The heater-A/C control RTM wire harness connector is still unplugged. Check for continuity between the A/C switch signal circuit cavity of the rear mode control motor wire harness connector and a good ground. There should be no continuity If OK, go to Step 10. If not OK, repair the short circuit as required.
9. Check for continuity between the A/C switch signal circuit cavities of the rear mode control motor wire harness connector and the heater-A/C control RTM wire harness connector. There should be continuity If OK, replace the faulty rear mode control motor. If not OK, repair the open circuit as required.