Chart 11, Rear Defroster Inoperative (TORONADO)
The rear defroster is activated by the rear defroster button on the ECC panel. When the button is pressed, a serial data signal is sent to the BCM on circuit No. 800. The BCM calculates the "on-time" for the defroster and sends a serial data signal to the programmer. The circuits in the programmer then supply the ground for the rear defroster relay coil, which pulls the contacts closed, allowing current to flow to the defroster elements on the rear window.
NOTE:
Test numbers refer to numbers on diagnostic chart.
- This step checks to see if the BCM is able to send and receive serial data signals between the HVAC programmer and the ECC panel.
- Since the signal from the rear defroster button is a serial data signal, this step checks to see if the button is functional by using it to exit diagnostics.
- This step checks for power at both relay terminals.
- This step checks for an open circuit No. 291 or a faulty programmer. The test light should normally light when the rear defroster button is pressed. This shows that the serial data signal was processed and the ground was supplied by the programmer to the relay on circuit No. 291.
- This step determines whether the fault is in the relay, in the output to the defroster, or ground. Normally, by jumpering the terminals, the defroster will operate if the circuits are complete.