What does it mean?
B1688 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Lamp Dome Input Circuit Short to Ground .
Symptoms
- Interior lamps stay on all the time and will not switch off
- Battery goes flat overnight or after the vehicle stands for a couple of days
- Door ajar warning displayed permanently even with all doors closed
- The interior lamps cannot be switched off with the dimmer or the override switch
- Alarm system arms incorrectly or triggers by itself
- Automatic locking and the delayed lamp switch off no longer work
Likely causes
- Door latch or door ajar switch stuck closed or internally shorted, which is the most frequent cause
- Water inside a door latch assembly, corroding the switch contacts so they never open
- Chafed wire in the flexible boot between a door and the body, touching the door shell
- Dome lamp override on the headlamp switch or the dimmer wheel left in the permanently on position, or the switch worn internally
- Wire pinched behind the headliner, the A pillar trim or a sill panel after previous work
- Boot lid or tailgate switch shorted, since it usually shares the same input
- Failed input circuit in the body control module
How to fix it
- Watch the dome lamp input and every door ajar signal on live data while opening and closing each door, the boot lid and the bonnet
- Turn the dimmer wheel and the dome override through their full travel and check whether the input state changes
- Unplug the door latches one at a time and watch whether the input releases, which identifies the guilty switch
- Inspect the flexing wiring in the door boots for broken and grounded conductors
- With the suspect branch disconnected, measure the resistance between the input wire and ground; a low value confirms the short
- Check for pinched wiring behind trim panels that have been removed in the past
- Repair or replace the faulty latch, switch or harness section, then confirm the interior lamps time out normally and check for parasitic drain