What does it mean?
B1387 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Power Tailgate Sensor Pulse B Circuit Malfunction .
Symptoms
- The tailgate misjudges direction, stopping or reversing unexpectedly during travel
- Obstacle detection triggers with nothing in the way
- Power operation is disabled after repeated faults and the gate has to be worked by hand
- The gate may slam or overrun its normal stopping points
- Warning chime or message every time power operation is attempted
Likely causes
- Broken or chafed conductor in the pulse B wire where the harness flexes at the tailgate hinge
- Water and corrosion in the drive unit connector
- Failed hall element for the B channel inside the drive unit
- Shared 5 volt supply or ground for the pulse sensor lost or high resistance
- Terminal pushed back or corroded in the drive unit plug
- Drive gearbox worn or the target wheel damaged, so pulses are missing at certain positions
- Tailgate module input fault
How to fix it
- Watch both pulse channels on the scan tool while the gate is moved slowly and look for the B trace dropping out or stopping altogether
- Confirm the sensor supply and ground at the drive unit before replacing anything
- Inspect and dry the drive unit connector, and check the terminals for corrosion and push-back
- Flex the hinge boot harness during the test to reproduce an intermittent break
- Repair the pulse B wire with a proper crimped and sealed joint that will survive the flexing
- Replace the drive unit when its internal sensor is proven faulty
- Carry out the travel relearn afterwards and verify obstacle detection with a soft object