Powertrain, generic (extended)

P257D Engine Hood Switch Circuit Range/Performance

Check engine lightOn
EmissionsNot relevant
Drive cycleRequired
Limp modeNo

P257D is the plausibility fault of the engine hood switch. The line is electrically readable, but the value falls into a band the module regards as impossible, or two redundant switches disagree. Hood status matters because stop-start, hybrid and remote-start logic must never crank the engine while someone is working in the bay. GM's 2018 engine table 18OBDG04 rejects a resistance-coded switch reading between 1,281 and 1,404 ohms, or two discrete switches showing the same state, after 80 bad readings out of 100 taken every 12.5 ms (Type B, two trips); the 2019 hybrid table 19OBDG01 uses percentage windows instead. GM bulletin PIC6460 traces P257D on 2014–2020 Impalas to coolant creeping from the temperature sensor into the ECM connector. Hood ajar messages and blocked auto-stop are typical.

Likely causes

Hood switch or plunger worn, misadjusted or contaminated
Fluid or corrosion in the switch or ECM connector shunting the signal
Second hood switch or latch switch reporting a different state
Replacement switch with wrong resistance coding

Symptoms

  • Check engine lamp after two drives
  • Hood ajar message although the hood is closed
  • Auto stop-start or remote start not available

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–300
Time0.5–2 h

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

Parts involved

hood switch

Related codes

P254FP257EP257FP25A3

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.