Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Windshield Heater
The automatic temperature control (ATC) module controls operation of the windshield heater using the windshield heater relay in the battery junction box (BJB). The automatic temperature control (ATC) module switches the ground connection of the relay coil to operate the windshield heater. While the windshield heater relay is energized, a battery power feed is connected to each of the two windshield heater elements. Windshield heater operation is only enabled when the engine is running.
The automatic temperature control (ATC) module operates the windshield heater in heating cycles of varying power and time. The heating cycle used depends on the ambient air temperature and whether it is the initial or subsequent operation during the current Power mode cycle.
When the windshield heater switch is pressed, the automatic temperature control (ATC) module illuminates a light emitting diode (LED) in the switch and initiates the appropriate heating cycle. The light emitting diode (LED) remains illuminated until the windshield heater is selected off, the heating cycle is completed or the engine stops. If the engine stalls or turned off, windshield heating resumes if the engine is re-started within 20 seconds.
On the initial selection of the windshield heater, the automatic temperature control (ATC) module uses a short or long defrost phase at full power, followed by a low power phase. The defrost phase used depends on the ambient temperature. During the low power phase, the windshield heater relay is cycled off for 80 seconds and on for 40 seconds.
On subsequent operations, during the same Power mode cycle, the automatic temperature control (ATC) module operates the windshield heater at full power for a fixed time period.
| Phase | Time, minutes |
|---|---|
| Short defrost (-5°C (23°F) and above) | 3 |
| Long defrost (less than -5°C (23°F)) | 5 |
| Low power | 10 |
| Subsequent operation | 3 |
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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