What does it mean?
B1788 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Headlamp Leveling Motor Control Circuit Low .
Symptoms
- Headlamp beam stuck too low or too high and not responding to the level adjuster
- One lamp aims correctly while the other stays where it is
- Warning message about the lighting system on equipped vehicles
- Motor buzzes briefly at ignition on then stops, or makes no self-test movement at all
- Automatic levelling no longer corrects for load in the boot or rear seats
Likely causes
- Control wire chafed to ground behind the bumper, at the headlamp bracket or along the front panel
- Water in the headlamp housing corroding the levelling motor connector and grounding a pin
- Levelling motor with a shorted winding or a seized drive drawing excessive current
- Connector at the motor damaged or its pins pushed back after headlamp removal or bulb changing
- Ride height sensor or level adjuster input feeding a false demand on systems with automatic levelling
- Wiring damaged in a previous front-end repair or during aftermarket lighting work
- Lighting control unit output stage failure
How to fix it
- Read the codes and watch the levelling motors during the key-on self test to see which side does not move
- Inspect the motor connector at the rear of the headlamp for water, corrosion and pushed-back pins
- Disconnect the motor: if the fault changes to an open or high circuit, the motor is the load pulling the line down
- Back-probe the control wire and measure its voltage while commanding movement with the scan tool
- Check the control wire for continuity to ground along its route, especially behind the bumper and at brackets
- On automatic systems, check the ride height sensor signal and its linkage before condemning the motor
- Repair the wiring or replace the levelling motor, then reset and check headlamp aim; replace the control unit last