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.
Circuit/System Description
When The Rear Window Defogger Is Commanded On And The Outside Temperature Is Below 7°C (45°F), The A26 Heater And Air Conditioning User Interface Control - Front Will Send A Serial Data Message To The K219 Lighting Control Module To Command The E49 Windshield Heating Grid To Operate.
The K219 Lighting Control Module Will, Upon Receipt Of The Request, Will Provide B+ To The Control Circuit 5994 Which Energizes The PCB Kr166 Heated Windshield Relay. This Allows Battery Positive Voltage From The Relay Switched Input To Flow Through The Switch Contacts And Out The Relay Switched Output To The Control Circuit 2411 Causing The E49 Windshield Heating Grid To Operate. Battery Positive Voltage Is Supplied At All Times To The Relay Switched Input And The Relay Coil And Windshield Heating Grid Are Always Grounded.
NO RELATED
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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.