What it means
The intermediate shaft speed sensor B signal jumps or drops out intermittently. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
How it works
Intermediate shaft speed sensor B reports shaft rotation as electrical pulses, which the transmission control module uses to track gear operation. P2748 sets when sensor B's signal drops out or jumps intermittently, often as a loose connector or damaged harness loses contact with vibration or movement.
Common causes
Most likely first.
- Sensor connector not fully seated
- Harness chafed against transmission housing
- Connector with intermittent contact under vibration
Symptoms
- Check-engine or transmission warning light on
- Intermittent harsh or delayed shifts
- Speedometer or gear indication may behave erratically
- Transmission may enter limp mode
How to diagnose it
- Save freeze-frame data and review live sensor B speed alongside other shaft speeds to see when its signal drops out.
- Inspect sensor B's connector for incomplete seating, corrosion, moisture, or pins pushed back into the housing.
- Check the harness where it passes near the transmission housing for chafing, pinching, or damaged insulation.
- With live data monitored, gently move the sensor B connector and harness to see whether the reading cuts out.
- If movement does not reproduce the fault, test sensor B and its wiring for intermittent continuity against the manufacturer's specifications.
Common fixes
- Seat and secure sensor B's connector.
- Clean or repair corroded or damaged connector terminals.
- Repair chafed or pinched wiring and secure the harness away from the transmission housing.
- Replace sensor B if its signal remains intermittent with a sound connection and harness.
Can I keep driving?
Limit driving and avoid towing or hard acceleration because a signal dropout can cause sudden harsh shifts or limp mode. Stop if shifts become unpredictable or the transmission begins slipping.
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.