P27F1 code meaning
Transmission Range Control B Position Sensor/Switch Circuit Low
Powertrain system Generic code P27xx codes Check engine light
What P27F1 means
P27F1 reports a valve B position signal that has collapsed toward ground in GM's internal range selection. GM describes the trigger as a ground short or open circuit on the mode valve B sensor line and uses the same 0.414 V limit, 0.100 s debounce and 9 V minimum supply as on valve A; both table editions, 2018 and 2020, rate it Type A, MIL on the first trip. As long as P27F1 is active, the TCM cannot verify valve B and drops its movement test P27F0. Hall sensors need a supply and a ground, so a dead supply pin also produces a low reading. Typical repairs concern the internal harness, the pass-through seal or the sensor. Valve A's counterpart is P27ED; high is P27F2.
P27F1 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 P27F1
- MIL comes on on the first trip
- Neutral or drive engagement slow or blocked
Common causes of P27F1
- Most likelyValve B sensor line shorted to ground
- PossibleSensor supply missing at the internal connector
- PossibleHall sensor on mode valve B failed
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 P27F1 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. |
| F1 | The exact fault in that area. |
What to do next
- Note P27F1 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 P27F1
What does P27F1 mean?
P27F1 means "Transmission Range Control B Position Sensor/Switch Circuit Low". P27F1 reports a valve B position signal that has collapsed toward ground in GM's internal range selection. It is a generic code, so it means the same on every make.
Is it safe to drive with P27F1?
Drive gently and only to a workshop. With P27F1 the car can go into limp mode (reduced power) to protect itself.
Will P27F1 fail an emissions test?
Yes, it can. P27F1 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 P27F1 to fix?
Difficulty: hard. A typical repair takes 1 to 6 hours of work. This is a job for a workshop.
Will P27F1 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.