Powertrain, generic (extended)

P256E Engine Idle Speed Selector Sensor/Switch Circuit Intermittent/Erratic

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

P256E records an idle speed selector signal that drops out or flickers for short moments, more often than real switch use would cause. Since the selector is usually operated with the engine idling for long periods, engine vibration, a worn rocker switch or a loose crimp can be enough; each interruption can cancel the raised idle and make the engine fall back and rise again. Ram's 2012 chassis cab guide describes an Idle Up set speed that is entered when the function is activated, so repeated on-off events are noticeable as speed changes. No manufacturer publishes P256E. CARB requires circuit faults on monitored inputs to be watched continuously. A steady break would set P256A instead. The driver mainly notices an unsteady raised idle.

Likely causes

Worn rocker or toggle switch
Loose crimp or terminal in the selector circuit
Harness moving with engine vibration at idle

Symptoms

  • Raised idle drops out and comes back
  • Engine speed rises and falls at standstill
  • Code stored only intermittently

Repair estimate

DifficultyEasyDIY possible
Parts and labour€20–250
Time0.3–2 h

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

Parts involved

idle speed selector switch

Related codes

P256AP256BP256CP256D

References: law.cornell.edu, http:.