P27EF code meaning
Transmission Range Control B Position Sensor/Switch Circuit/Open
Powertrain system Generic code P27xx codes Check engine light
What P27EF means
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.
P27EF at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P27EF
- Transmission warning, neutral or drive engagement may be restricted
- Fault stored in the TCM
Common causes of P27EF
- Most likelyMode valve B sensor signal line interrupted
- PossibleHall sensor on mode valve B no longer switching cleanly
- PossibleFluid or corrosion at the transmission pass-through connector
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Range control position sensor bWiring harnessTCM
What each part of P27EF means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 7 | Area: transmission. |
| EF | The exact fault in that area. |
What to do next
- Note P27EF and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P27EF
What does P27EF mean?
P27EF means "Transmission Range Control B Position Sensor/Switch Circuit/Open". P27EF concerns the second mode valve, B, of GM's internal electronic range selection. It is a generic code, so it means the same on every make.
Is it safe to drive with P27EF?
Drive gently and only to a workshop. With P27EF the car can go into limp mode (reduced power) to protect itself.
Will P27EF fail an emissions test?
Yes, it can. P27EF is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P27EF to fix?
Difficulty: hard. A typical repair takes 1 to 6 hours of work. This is a job for a workshop.
Will P27EF clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.