P256AEngine Idle Speed Selector Sensor/Switch Circuit/Open
- Generic OBD-II code · Powertrain
- How the car detects it
- P256A refers to the switch or sensor with which the driver chooses a raised idle speed, for example to run a generator, an inverter or belt-driven equipment while parked, independent of any PTO. The controller sees no valid state on this input, which points to an open wire, a disconnected plug or a switch that no longer makes contact. No manufacturer documents P256A publicly. GM's bulletin PIT4529D for 2007–2018 Silverado/Sierra 2500/3500 shows that such selections exist side by side: an automatic cold-weather elevated idle on the 6.6L diesel, an optional High Idle (RPO UF3) operated through the cruise buttons, and a separate PTO mode. The engine keeps its normal idle; P0506 and P0507 instead concern an idle that misses its target.
- What you may notice
- Raised idle cannot be selected
- Engine stays at normal idle
- Likely causes
- LikelyOpen wire in the idle selector circuit
- PossibleSelector connector loose or not mated
- PossibleIdle selector switch without contact
- Repair
- Easy · Often possible to do yourself.Typical cost: €20 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.