Powertrain, generic (extended)

P27F0 Transmission Range Control B Position Sensor/Switch Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

P27F0 checks whether mode valve B really moves. In GM's 2020 table for the T87A 10-speed RWD transmission, the TCM expects the valve B sensor to follow commands to park, reverse, neutral high or low, neutral shift and drive within a delay; if the final state is not reached under adequate line pressure, the Type A code sets. The electrical sensor codes P27EF, P27F1 and P27F2 must be clear for the test to run. In GM bulletin 21-NA-169, aimed at 9T45/50/60 automatics with under 19,000 km, P27F0 sits beside P27EC in the group where the valve body is replaced if the fluid looks healthy; dark, burnt fluid means the clutches need inspection too. Drivers notice delayed or refused range changes.

Likely causes

Mode valve B sticking in the valve body
Insufficient line pressure to move the valve
Position sensor B reporting late or wrong state

Symptoms

  • Delay or refusal when selecting neutral, drive or reverse
  • MIL on, transmission may enter a protective 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 bvalve bodywiring harnesstcm

Related codes

P27EFP27F1P27F2P27EC

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