Powertrain, generic (extended)

P256C Engine Idle Speed Selector Sensor/Switch Circuit Low

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P256C says the idle speed selector input is pulled below its lowest valid level, typically by a signal wire shorted to ground or a switch with an internal short. Where the selector is a simple ground-switched input, the controller would read such a short as a permanent request, so a dedicated low code presupposes a coded or monitored circuit. No manufacturer documents P256C publicly. A raised idle that appears without driver input is not automatically this fault: Ram's 2025 6.7L Cummins bulletin S2509000007 lists automatic modes such as cab warm-up at 1000 rpm below 4.4 °C ambient or inverter support between 700 and 1500 rpm. P256D is the high-side code. Expect the raised idle to be unavailable or the code to return after every key cycle.

Likely causes

Idle selector wire shorted to ground
Internal short in the idle selector

Symptoms

  • Raised idle unavailable
  • Code returns after every key cycle

Repair estimate

DifficultyEasyDIY possible
Parts and labour€20–250
Time0.3–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

idle speed selector switch

Related codes

P256AP256BP256DP256EP0507

References: law.cornell.edu, static.nhtsa.gov.