Faulty rear defrost switch (worn contacts or internal failure).; Open or shorted wiring in the rear defrost switch circuit.; Corroded or loose electrical connector at the switch or control module.; Blown fuse or faulty relay supplying power to the switch circuit.; Failed body control module (BCM) or rear defrost control module.; Water intrusion or physical damage to the switch or wiring harness.

DTC codes / B02xx · Airbags, seats, doors, lights and comfort systems / B0290

B0290Rear Defrost Switch Circuit

Q: What does code B0290 mean?

Rear Defrost Switch Circuit. B0290 indicates that the body control module (BCM) or rear defrost control module has detected an abnormal condition in the rear defrost switch circuit, such as an open, short, or unexpected voltage. The computer monitors the switch input and sets this code when the signal does not match the expected state for the rear defrost activation request.

B0290 indicates that the body control module (BCM) or rear defrost control module has detected an abnormal condition in the rear defrost switch circuit, such as an open, short, or unexpected voltage. The computer monitors the switch input and sets this code when the signal does not match the expected state for the rear defrost activation request.

SystemBody

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaAirbags, seats, doors, lights and comfort systems

Symptoms you may notice

The rear defrost indicator light may fail to illuminate when the button is pressed.
The rear window defroster may not activate at all, leaving the glass fogged or frosted.
The defroster may stay on continuously regardless of switch position.
In some vehicles, the HVAC control panel backlighting or other functions on the same circuit may be inoperative.
Often no symptoms besides the warning light, especially if the switch is only intermittently faulty.

Common causes, most likely first

Faulty rear defrost switch (worn contacts or internal failure).
Open or shorted wiring in the rear defrost switch circuit.
Corroded or loose electrical connector at the switch or control module.
Blown fuse or faulty relay supplying power to the switch circuit.
Failed body control module (BCM) or rear defrost control module.
Water intrusion or physical damage to the switch or wiring harness.

How to diagnose and fix it

Verify the fault by checking for related diagnostic trouble codes (DTCs) and inspecting the rear defrost switch for physical damage or sticking.
Check the fuse and relay associated with the rear defrost circuit, replacing any that are blown or faulty.
Disconnect the switch and inspect the connector terminals for corrosion, tightness, and proper pin fit.
Use a digital multimeter (DMM) to measure resistance and continuity across the switch in both on and off positions, comparing to manufacturer specifications.
Backprobe the switch connector to check for reference voltage and ground signals with the key on, ensuring the BCM is sending and receiving the correct signals.
If the switch and wiring test good, substitute a known-good switch or module to see if the code clears and the system operates correctly.
Clear the DTC and verify the repair by operating the rear defrost and confirming no code returns after a complete drive cycle.

Before you replace the rear defrost switch

A common misdiagnosis is replacing the switch when the real problem is a corroded ground connection shared with other dashboard components, which can mimic a switch failure.
The BCM often logs B0290 if battery voltage is low or unstable during cranking, so always check the battery and charging system before condemning the switch.
On some vehicles, the rear defrost switch is integrated into the HVAC control head, and a fault in that assembly can set B0290 even though the switch itself is fine.
Intermittent faults often occur due to a chafed wire in the flexible conduit between the body and the liftgate, which is easy to overlook during a visual inspection.
The code can be set by a stuck relay that keeps the defroster on, so testing the relay for proper operation is a quick and often missed step.

Can I keep driving with B0290?

The vehicle remains safe to drive because the rear defrost is a convenience feature and does not affect engine operation or safety systems. Avoid using the rear defrost until the fault is repaired, as a short circuit could drain the battery or cause further electrical damage.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.