P257DEngine Hood Switch Circuit Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Needs a drive cycle to confirm a fix
- How the car detects it
- 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.
- What you may notice
- Check engine lamp after two drives
- Hood ajar message although the hood is closed
- Auto stop-start or remote start not available
- Likely causes
- LikelyHood switch or plunger worn, misadjusted or contaminated
- PossibleFluid or corrosion in the switch or ECM connector shunting the signal
- PossibleSecond hood switch or latch switch reporting a different state
- RareReplacement switch with wrong resistance coding
- Repair
- Medium · Often possible to do yourself.Typical cost: €30 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.