Faulty driver's mirror adjustment switch (most common).; Damaged or corroded wiring harness between the switch and the body control module.; Loose or dirty electrical connector at the switch or mirror motor.; Failed mirror motor or mirror assembly (though this usually sets a different code).; Water intrusion into the switch or connector causing corrosion.; Body control module (BCM) internal fault (rare).

DTC codes / B01xx · Airbags, seats, doors, lights and comfort systems / B0104

B0104Driver Mirror Adjust Switch Circuit

Q: What does code B0104 mean?

Driver Mirror Adjust Switch Circuit. B0104 indicates that the body control module (BCM) has detected a fault in the electrical circuit for the driver's side mirror adjustment switch. The BCM monitors the switch inputs and expects to see specific voltage signals when the switch is moved; when the voltage stays out of range or the circuit is open or shorted, the BCM stores this code.

B0104 indicates that the body control module (BCM) has detected a fault in the electrical circuit for the driver's side mirror adjustment switch. The BCM monitors the switch inputs and expects to see specific voltage signals when the switch is moved; when the voltage stays out of range or the circuit is open or shorted, the BCM stores this code.

SystemBody

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaAirbags, seats, doors, lights and comfort systems

Symptoms you may notice

The driver's side mirror does not adjust in one or more directions when the switch is operated.
The mirror may move in only one direction or not at all, regardless of switch position.
The mirror adjustment switch may feel loose or unresponsive.
Often no symptoms besides the warning light, especially if the fault is intermittent.
The mirror may move unexpectedly or stick in one position.
Other memory or power functions on the driver's seat or mirror may also be affected if they share the same switch module.

Common causes, most likely first

Faulty driver's mirror adjustment switch (most common).
Damaged or corroded wiring harness between the switch and the body control module.
Loose or dirty electrical connector at the switch or mirror motor.
Failed mirror motor or mirror assembly (though this usually sets a different code).
Water intrusion into the switch or connector causing corrosion.
Body control module (BCM) internal fault (rare).

How to diagnose and fix it

Inspect the driver's mirror adjustment switch for physical damage, sticking, or contamination.
Check the wiring harness and connectors at the switch and mirror for corrosion, loose pins, or chafed wires.
Use a scan tool to view live data for the mirror switch inputs while operating the switch to confirm the BCM is seeing the correct signals.
Perform a resistance test on the switch in each position to verify it opens and closes correctly.
Check for continuity and voltage drops on the circuit between the switch and BCM according to the factory wiring diagram.
If the switch tests bad, replace it; if wiring is faulty, repair the harness.
Clear the code and verify the repair by operating the mirror in all directions and confirming the code does not return.

Before replacing the mirror switch

A common misdiagnosis is replacing the mirror motor when the actual fault is a dirty or worn switch inside the driver's door panel.
Intermittent B0104 codes often result from a loose connector that only loses contact when the door is slammed or the vehicle hits a bump.
The driver's mirror switch often shares a ground with other door functions; a bad ground can cause multiple seemingly unrelated codes.
Water leaks from the window seal or door handle can corrode the switch contacts and set this code without any visible external damage.
Some vehicles require programming or calibration of the mirror module after switch replacement, so consult the factory service information.

Can I keep driving with B0104?

The vehicle remains safe to drive because the mirror adjustment is a convenience feature and does not affect steering, braking, or visibility when the mirror is already positioned. Avoid adjusting the mirror repeatedly if the switch feels stuck, as this could worsen the fault, and have it repaired at your convenience.

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.