What does it mean?
B1870 is a Body (airbags, seat belts, body electronics) fault code. It indicates: All Door Secondary Lock Control Circuit High .
Symptoms
- Doors will not deadlock, or the double lock function is disabled
- Central locking works from inside but not from the key fob, or only some doors respond
- Audible relay or actuator chatter when locking
- Security indicator behaves abnormally and the alarm may not arm
- Parasitic battery drain if the output driver is stuck energised
Likely causes
- Control wire shorted to a battery feed inside a door or behind the trim
- Water intrusion in a door jamb connector bridging the lock control pin to a powered pin
- Failed deadbolt actuator with a shorted or burnt winding
- Aftermarket alarm or remote start spliced into the lock control circuit
- Corroded or spread terminals at the actuator connector
- Body control module output driver failure
- Poor module ground raising the reference so the driver reads high
How to fix it
- Retrieve the code and freeze frame, then note whether the fault is present with the doors locked, unlocked or both
- Watch the lock output state in scan tool live data and command a lock and unlock cycle bidirectionally
- Unplug the deadbolt actuators one at a time and see which one clears the high reading, which isolates a shorted actuator from a shorted wire
- With the module connector disconnected, check the control circuit for voltage present with the ignition off; any voltage indicates a short to a power feed
- Inspect the door jamb boots and jamb connectors for chafing, water and corrosion
- Check for aftermarket splices in the lock circuit and remove any that are not factory
- Repair the wiring or replace the faulty actuator, then verify module ground quality with a voltage drop test before condemning the module