What does it mean?
B1591 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Turn Signal Multifunction Switch Error .
Symptoms
- The headlamp-off delay cannot be shortened, so the lamps burn long after the driver has left
- Battery goes flat because the headlamps stay on for the maximum delay every time
- The delay setting resets or is ignored on each key cycle
- The control feels normal but the vehicle does not react to the lower settings
- On the multifunction variant, turn signals, high beam or flash-to-pass work intermittently or need the stalk to be held
Likely causes
- Worn contacts on the decrease side of the autolamp delay control, so the shorter settings are never selected
- Corrosion or a loose terminal at the control connector
- Chafed or broken wire between the control and the module behind the dash
- Liquid ingress into the control head or the stalk assembly
- Poor ground or an unstable reference at the control
- Module input stage failure
- On applications where these functions sit on the combination stalk, an internal fault in the multifunction switch that also carries the turn signal circuits
How to fix it
- Step the delay control through each position while watching the value in live data and note which steps are missing
- Back-probe the decrease input at the module and confirm the voltage changes cleanly at every detent
- Check continuity through the control at each position rather than only at the extremes
- Inspect the connector at the stalk or control head for corroded and spread terminals
- Look at the loom behind the column for chafe, especially where it passes the tilt mechanism
- If the functions share a combination stalk, test the turn signal and high beam circuits as well, since a common fault points to the switch rather than the harness
- Replace the switch or control head last, only after the wiring, ground and reference have been proven good