What it means
The gear shift position circuit B reports a circuit low fault. Gear shift position feedback is unreliable on this channel.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Gear shift position circuit B provides a second position feedback signal to the TCM. P091C sets when the B-channel signal falls below its expected electrical range, so the module cannot reliably use that channel to confirm shift position.
Common causes
Most likely first.
- Position sensor failed
- Wiring fault
- Connector pins corroded - high contact resistance
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
How to diagnose it
- Record freeze-frame data and check circuit B live data to see whether the low reading is constant or tied to a particular shift.
- Inspect the B-channel sensor connector and harness for corrosion, water, damaged insulation, loose pins, or a signal wire shorted to ground.
- Following the wiring diagram, check circuit B reference supply and ground, then test the signal wire for a short to ground or open.
- Move the selector while monitoring circuit B and gently flex its harness to check for a low reading caused by a poor connection.
- If wiring and supplies are sound, test the circuit B position sensor output against the manufacturer's specification.
Common fixes
- Repair a circuit B signal wire shorted to ground or open in the harness.
- Clean or replace corroded B-channel terminals and restore the connector seal.
- Repair a poor circuit B sensor ground or reference connection.
- Replace the circuit B position sensor if its signal remains low with sound wiring.
Can I keep driving?
Avoid driving if the transmission selects gears unpredictably, slips, or enters limp mode; arrange recovery if control is uncertain. Continued operation with unreliable circuit B feedback can worsen shift quality or leave the vehicle in a limited gear.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.