Powertrain, generic (extended)

P27ED Transmission Range Control A Position Sensor/Switch Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P27ED tells that the Hall sensor on mode valve A of GM's internal range selection delivers almost no voltage. In both the 2018 9-speed and the 2020 10-speed RWD tables the limit is a raw value under 0.414 V for 0.100 s within 0.163 s, with at least 9 V on the battery; GM itself blames a grounded or interrupted line. The code is Type A and lights the MIL on the first trip. Because the TCM then cannot confirm whether the valve has left park, the movement check P27EC is suspended while P27ED is active. Look at the sensor connector inside the transmission and the pass-through plug. High is P27EE, the invalid middle band P27EB, and valve B uses P27F1 for the same fault.

Likely causes

Sensor signal shorted to ground in the internal harness
Sensor supply open, output collapses
Hall sensor on mode valve A failed

Symptoms

  • MIL lit immediately
  • Shifts out of park slow or blocked

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 awiring harnesstcm

Related codes

P27EBP27ECP27EEP27F1

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