What it means
The gear shift position circuit B reports a circuit 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 carries a second position feedback signal to the TCM, which uses it to check the shift mechanism's position. P091A sets when the module detects a fault in this B channel and cannot rely on its feedback.
Common causes
Most likely first.
- Position sensor failed
- Wiring fault
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
- Save freeze-frame data and compare circuit B live position data with the selected and commanded gear to see when the channel becomes unreliable.
- Inspect the circuit B sensor connector and wiring separately from circuit A for loose terminals, corrosion, moisture, or physical damage.
- Use the wiring diagram to check circuit B power, ground, and signal paths for opens, shorts, or poor connections.
- Monitor circuit B live data while selecting each gear and note readings that are missing, stuck, or inconsistent.
- If the wiring checks out, test the circuit B position sensor against the manufacturer's specification.
Common fixes
- Reconnect a loose circuit B sensor connector and repair damaged wiring.
- Clean or replace corroded circuit B terminals and restore connector sealing.
- Repair an open, short, or poor ground in the circuit B wiring.
- Replace the circuit B position sensor if its feedback fails testing.
Can I keep driving?
If shifting remains predictable, limit driving to a short trip for diagnosis and stop if gears become unavailable or erratic. The TCM may restrict operation or enter limp mode when circuit B feedback cannot be trusted.
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.