What does it mean?
B1580 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Ignition Start Switch Short High .
Symptoms
- Dash illumination cannot be brightened; the level stays where it is or falls to minimum
- The control feels normal to operate but nothing changes on the display
- Cluster and radio backlighting respond differently from each other
- Brightness resets to a default level on every key cycle
- On the start switch variant, the starter engages unexpectedly or the crank request stays present after the key is released
Likely causes
- Open circuit in the wire between the panel dimmer control and the module
- Worn or dirty wiper track inside the dimmer rheostat, giving a dead spot on the increase side
- Connector not fully seated after dash or cluster work, or a terminal backed out of its housing
- Missing reference or ground for the dimmer control
- Corroded splice in the illumination control circuit behind the dash
- Module or cluster input open internally
- On applications where this code refers to the ignition start switch, a start signal shorted high that keeps the crank request active
How to fix it
- Watch the panel dimmer value in live data while turning the control through its full sweep and note whether it ever rises
- Back-probe the increase wire at the module and check that the voltage changes when the control is moved
- Test the dimmer control for continuity across its whole range and look for dead spots rather than only checking the ends
- Verify the reference and ground supplied to the control before replacing it
- Inspect the connector for backed-out terminals, which is common after previous dash work
- Repair the open circuit, replace the control only if it fails the sweep test, and leave the cluster or module for last
- On the start switch variant, measure the start signal with the key released and check the switch for sticking contacts