What it means
The TCM cannot read a valid signal from the clutch A motor rotor position sensor. Open wiring or sensor failure.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
The clutch A motor position sensor reports rotor position to the TCM so it can control motor commutation and clutch movement. P28CB sets when the TCM cannot read a valid sensor signal, commonly because the signal circuit is open, the sensor has failed, or a connector pin has backed out.
Common causes
Most likely first.
- Open in sensor signal wire
- Position sensor failed
- Pin pushed back out of connector body
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 the freeze-frame data and check transmission live data for a missing or invalid clutch A motor position reading.
- With ignition off, inspect the clutch A position sensor connector for a pushed-back pin, incomplete engagement, corrosion, or damage.
- Trace the sensor signal wire and check for an open circuit or damaged insulation between the sensor and TCM, using the manufacturer's wiring information.
- Check the sensor supply and ground circuits against the manufacturer's procedure before condemning the sensor.
- If wiring and connector continuity are good, test the clutch A position sensor output and replace it only if it fails the manufacturer's specification.
Common fixes
- Reseat the clutch A position sensor connector and secure any backed-out pin.
- Repair an open or damaged sensor signal wire.
- Clean or replace a damaged connector terminal.
- Replace the clutch A motor position sensor if circuit checks pass but its signal remains invalid.
Can I keep driving?
Avoid normal driving if shifts are delayed, harsh, or missing, since the TCM may limit the transmission to one gear. Arrange prompt diagnosis and stop if the vehicle loses drive or shifts unpredictably.
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.