Powertrain, generic (extended)

P27EF Transmission Range Control B Position Sensor/Switch Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Mode valve B sensor signal line interrupted
Hall sensor on mode valve B no longer switching cleanly
Fluid or corrosion at the transmission pass-through connector

Symptoms

  • Transmission warning, neutral or drive engagement may be restricted
  • Fault stored in the TCM

Repair estimate

DifficultyHardWorkshop job
Parts and labour€150–2,000
Time1–6 h

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

Parts involved

range control position sensor bwiring harnesstcm

Related codes

P27F0P27F1P27F2P27EB

References: gsi.ext.gm.com, gsi.ext.gm.com.