P27EFTransmission Range Control B Position Sensor/Switch Circuit/Open
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P27EF concerns the second mode valve, B, of GM's internal electronic range selection. Its Hall sensor is expected to sit clearly high or clearly low; GM's 2018 9-speed and 2020 10-speed RWD tables treat a raw value between 1.263 and 1.504 V, held for 0.100 s of a 0.163 s sample, as an illegal level. A level in that gap typically comes from an interrupted signal line or a sensor that has stopped switching. The tables show the same timing as for valve A, but the MIL column for P27EF is left blank in both editions, so the illumination type is not stated. Mode valve B is involved in neutral and drive states, so shifting may be limited. Low and high are P27F1 and P27F2, the movement test P27F0.
- What you may notice
- Transmission warning, neutral or drive engagement may be restricted
- Fault stored in the TCM
- Likely causes
- LikelyMode valve B sensor signal line interrupted
- PossibleHall sensor on mode valve B no longer switching cleanly
- PossibleFluid or corrosion at the transmission pass-through connector
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €150 – €2,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.