What does it mean?
B1550 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Mirror LF/RF Select Switch Circuit .
Symptoms
- One or more windows do not work from the master switch, although the individual door switch still works
- A window goes up or down on its own without any command
- The window lock function stops working or locks out all windows permanently
- Door module stays awake with the key out and the battery goes flat overnight
- Windows work erratically in wet weather and improve when the door dries out
- On the mirror select variant, the switch adjusts the wrong mirror or both at once
Likely causes
- Water intrusion into the driver door master switch, usually after a blocked door drain or a torn vapour barrier
- Master switch wire chafed against the door structure or the window regulator, shorting the circuit to ground
- Switch contact stuck or welded closed, holding the request permanently active
- Bent or corroded terminal in the master switch connector bridging to the ground pin
- Loom pinched inside the door hinge boot where it flexes
- Damage from a previous speaker, mirror or door trim installation
- Failed input stage in the driver door module
- On applications where this code refers to the mirror select switch, a shorted select contact inside the same switch pack
How to fix it
- Read the freeze frame data and confirm whether the fault is present now or only stored
- Unplug the master switch and see whether the code stops resetting, which separates the switch from the harness immediately
- With the switch unplugged, measure the suspect circuit to ground: it should read open, and a near-zero value confirms a short
- Remove the door trim and inspect the switch for water; many master switches can be dried and cleaned rather than replaced
- Check the vapour barrier and the door drain holes, because water is the root cause in most of these failures
- Inspect the loom in the hinge boot for insulation worn down to the copper
- Verify module supply and ground, then repair the harness or replace the switch; leave the module for last