P27F1Transmission Range Control B Position Sensor/Switch Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P27F1 reports a valve B position signal that has collapsed toward ground in GM's internal range selection. GM describes the trigger as a ground short or open circuit on the mode valve B sensor line and uses the same 0.414 V limit, 0.100 s debounce and 9 V minimum supply as on valve A; both table editions, 2018 and 2020, rate it Type A, MIL on the first trip. As long as P27F1 is active, the TCM cannot verify valve B and drops its movement test P27F0. Hall sensors need a supply and a ground, so a dead supply pin also produces a low reading. Typical repairs concern the internal harness, the pass-through seal or the sensor. Valve A's counterpart is P27ED; high is P27F2.
- What you may notice
- MIL comes on on the first trip
- Neutral or drive engagement slow or blocked
- Likely causes
- LikelyValve B sensor line shorted to ground
- PossibleSensor supply missing at the internal connector
- PossibleHall sensor on mode valve B failed
- 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.