P27F0 code meaning
Transmission Range Control B Position Sensor/Switch Circuit Range/Performance
Powertrain system Generic code P27xx codes Check engine light
What P27F0 means
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.
P27F0 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyWorkshop only
- Typical labor2 to 8 hours
- Clears after repairAfter a drive cycle
Symptoms of P27F0
- Delay or refusal when selecting neutral, drive or reverse
- MIL on, transmission may enter a protective mode
Common causes of P27F0
- Most likelyMode valve B sticking in the valve body
- PossibleInsufficient line pressure to move the valve
- Less likelyPosition sensor B reporting late or wrong state
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 bValve bodyWiring harnessTCM
What each part of P27F0 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. |
| F0 | The exact fault in that area. |
What to do next
- Note P27F0 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 P27F0
What does P27F0 mean?
P27F0 means "Transmission Range Control B Position Sensor/Switch Circuit Range/Performance". P27F0 checks whether mode valve B really moves. It is a generic code, so it means the same on every make.
Is it safe to drive with P27F0?
Drive gently and only to a workshop. With P27F0 the car can go into limp mode (reduced power) to protect itself.
Will P27F0 fail an emissions test?
Yes, it can. P27F0 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 P27F0 to fix?
Difficulty: workshop only. A typical repair takes 2 to 8 hours of work. This is a job for a workshop.
Will P27F0 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.