Powertrain, generic (extended)

P27EC Transmission Range Control A Position Sensor/Switch Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P27EC is GM's movement check for mode valve A of its internal range selection: after the TCM commands park, drive or reverse, the position sensor must report the new state within a set delay; the logic also watches line pressure and clutch slip. Both the 2018 nine-speed and 2020 ten-speed tables rate it Type A. Bulletins show it is often hydraulic: 21-NA-169 has the valve body replaced on low-mileage 9T45/50/60 units when P27EC or P27F0 appear with clean fluid, PIP6069 says to renew the valve body rather than the TCM on 2024 full-size trucks and SUVs with the 10L80, and 19-NA-200 notes that on the 2025 Equinox a failed auxiliary pump or harness sets P27EC before P2797.

Likely causes

Mode valve A sticking inside the control valve body
No hydraulic pressure from a failed auxiliary pump during auto stop
Mode valve A position sensor reading wrong

Symptoms

  • Delayed or refused shift into park, drive or reverse
  • MIL on, stop-start may be disabled
  • Transmission in reduced operating mode

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€300–3,000
Time2–8 h

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

Parts involved

range control position sensor avalve bodywiring harnesstcm

Related codes

P27EBP27EDP27EEP27F0P2797

References: gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov, static.nhtsa.gov.