What does it mean?
B1720 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Mirror Up and Down Control Switch Circuit .
Symptoms
- Mirror glass will not tilt up or down while the left and right movement still works
- One mirror affected or both, depending on how the select switch is wired
- Mirror jumps briefly and then stops when the switch is pressed
- Memory mirror positioning does not complete on unlock or on driver profile change
- Power fold or heating on the same connector may act up at the same time
Likely causes
- Worn or dirty contacts inside the mirror joystick, so the vertical channel never gives a clean value
- Liquid spill into the door-mounted switch pack
- Broken wire in the rubber boot between the door and the A-pillar, where the loom flexes every time the door opens
- Corroded or water-damaged door connector after a leaking door membrane
- Left/right mirror select switch shorting the vertical line
- Door or body control module input fault
How to fix it
- Read the codes and watch the vertical switch channel live while operating the joystick in both directions
- Remove and inspect the switch pack for corrosion, sticky residue or worn contacts, and clean it
- Substitute a known good switch pack if one is available before condemning wiring
- Open the rubber door boot and flex the loom by hand while watching for the signal to drop out
- Check continuity and resistance of the vertical control wires from switch connector to mirror and to the module
- Repair broken conductors inside the boot with proper soldered and sealed joints
- Replace the mirror actuator or the door module only after switch and wiring are proven