P1687 Automatic transmission FI signal B high input
What does P1687 mean on a Honda?
P1687. Automatic transmission FI signal B high input. This Honda-enhanced code applies to 1999 to 2003 TL, CL and Accord V6 with automatic.
Common causes of P1687
- Short to power on signal B wire
- Failed signal B driver stuck high
- Corroded connector pins
- Poor module ground
- Faulty ECM input circuit
How to fix P1687
- Check module grounds
- Inspect signal B wire routing
- Measure signal B voltage key on
- Repair short to power found
- Replace the failed module after wiring checks
Sources and review
- Last updated 2026-09-24.