P0580Cruise Control Multi-Function Input "A" Circuit Low
The multiplexed cruise control switch circuit voltage is below its expected range, usually from a short to ground.
Definition
On vehicles that run the cruise buttons through a single multi-function input, the module reads a voltage-coded signal that should never fall below the lowest valid button value. P0580 sets when the circuit voltage drops under that minimum, which indicates a short to ground in the harness, a shorted switch, or a clockspring fault. The module disables cruise control as a failsafe to prevent misread commands; there is no MIL, driveability, or emissions impact. This code frequently appears on GM trucks with damaged column wiring or liquid-contaminated switch pads.
Common causes
- Cruise switch signal wire shorted to ground
- Internally shorted cruise control switch assembly
- Failed or shorted clockspring circuit
- Liquid intrusion in the steering-wheel switch pad
- Corroded or damaged column connector
- Faulty module input circuit (rare)
Common misdiagnoses
- Replacing the brake light switch
- Replacing the body control module or PCM before isolating the harness short
- Replacing the cruise servo/actuator
- Replacing the steering wheel when only the switch or clockspring is faulty
Troubleshooting steps
1.Measure the circuit voltage at rest
Back-probe the multi-function input with the key on; a reading below the lowest valid button step confirms the circuit is pulled low.
2.Disconnect the switch to split the circuit
If voltage recovers to the at-rest specification with the switch unplugged, replace the switch; if it stays low, the fault is in the harness or clockspring.
3.Ohm the harness to ground
With both ends disconnected, check the signal wire for continuity to chassis ground and repair any chafe found.
4.Test the clockspring
Check for shorts between spiral cable circuits while rotating the wheel lock-to-lock.
5.Verify the repair
Confirm each button produces its correct voltage step, clear the code, and road test cruise engagement and all functions.