What it means
The gear shift position circuit B reports a circuit range/performance 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 feedback signal that the TCM checks against the shift command and expected position. P091B sets when the B-channel reading is outside its expected range or does not perform as expected, which may result from a drifting sensor or a circuit fault.
Common causes
Most likely first.
- Position sensor failed
- Wiring fault
- Sensor element aged beyond calibration window
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
- Review freeze-frame data and compare circuit B's reported position with commanded gear to identify the position or transition outside the expected range.
- Watch circuit B live data while selecting each gear and check for out-of-sequence, unstable, or implausible readings.
- Inspect the B-channel sensor mounting, connector, and harness for misalignment, looseness, corrosion, or damage.
- Check circuit B power, ground, and signal wiring for opens, shorts, or poor contact using the wiring diagram.
- If the mechanical alignment and wiring are sound, test circuit B sensor response across its range against the manufacturer's specification.
Common fixes
- Correct loose or misaligned mounting that affects circuit B position feedback.
- Repair damaged circuit B wiring or connector contacts.
- Adjust the linkage if actual shift position does not match the sensor's reported position.
- Replace the circuit B position sensor if its response is out of range or drifts beyond specification.
Can I keep driving?
Limit driving if shifts remain predictable, and avoid long trips or heavy loads until the position mismatch is diagnosed. Stop if the transmission slips or fails to engage, as unreliable feedback can disrupt gear changes.
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.