P256B
Engine Idle Speed Selector Sensor/Switch Range/Performance
The idle-speed selector input is electrically intact but the value does not match a valid preset — multiple positions or a non-mappable value. Often a sticky multi-position switch.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Symptoms
- Check engine light on
- Idle speed too high, too low, or unstable
- Possible stalling at idle or after cold start
Common causes
Ordered by how often each turns out to be the cause.
- Contaminated rotary contactCommon
- Sensor element aged beyond calibration windowLess likely
- Sensor mounting loose - signal dampingLess likely
Parts involved
- Idle Speed Selector Switch
P256B is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.