Powertrain, generic (extended)

P2509 ECM/PCM Power Input Signal Intermittent

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P2509 records a brief loss of the engine module's supply, a dropout rather than a lasting low or high value. Two Cummins-powered pickups show how easily it appears. Nissan warns for the 2016 Titan XD with the 5.0 L diesel: wait at least two minutes after switching off before disconnecting either 12 V battery, otherwise P2509 and P181B are stored; such codes may be erased but are not a warranty repair. FCA lists P2509 among faults addressed by a PCM reflash for 2018 Ram 2500/3500 with the 6.7 L Cummins, where customers saw the MIL. The module's after-run, interrupted by a cut supply, is what the check catches. Persistent values belong to P2507 and P2508, plausibility to P2506. Real loose battery clamps or relay contacts give the same code.

Likely causes

Battery disconnected before the module finished its after-run
Loose battery clamp, ground or supply connector
Module software too sensitive, fixed by reflash (Ram 6.7 L)
Intermittent main relay contact

Symptoms

  • MIL on, often without drivability complaint
  • Code appears right after battery work

Repair estimate

DifficultyEasyDIY possible
Parts and labour€0–300
Time0.2–1.5 h

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

Parts involved

ecu power supplymain relaybattery terminals

Related codes

P2505P2506P2507P2508

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