What it means
The two redundant throttle position sensors on the throttle body disagree by more than allowed. Distinct from P2138 which monitors the pedal pair — P2135 monitors the throttle-body pair on drive-by-wire systems.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The throttle body has two position-sensor tracks, A and B, that provide redundant feedback about throttle plate movement. P2135 sets when the control module finds that the A and B throttle-body signals do not maintain their expected relationship, prompting many vehicles to restrict throttle operation.
Common causes
Most likely first.
- Throttle position sensor track worn
- Corrosion on throttle body connector
Symptoms
- Check engine light on
- Reduced throttle response, possible limp mode
- Hesitation or surging
- Idle too high or too low
How to diagnose it
- Record freeze-frame data and graph throttle position sensor A and B while commanding a gradual throttle change; check where their relationship first becomes implausible.
- Inspect the throttle-body connector and nearby wiring for corrosion, loose or pushed-back pins, damage, or contamination that could affect either track.
- Check both sensor circuits for secure power, ground, and signal connections, comparing readings with the manufacturer's specification.
- With the throttle body connected, compare A and B signal changes through the operating range using the scan tool; look for a track that sticks, jumps, or diverges.
- If the circuits are sound but the signals disagree, inspect or test the throttle body and position sensor assembly according to the manufacturer's procedure.
Common fixes
- Clean and secure corroded or loose throttle-body connector terminals.
- Repair damaged wiring or poor power, ground, or signal connections to the A/B sensor circuits.
- Replace the throttle body or its position-sensor assembly if the A and B tracks fail the manufacturer's tests.
- Repair a verified control-module fault only after the sensor and circuit checks pass.
Can I keep driving?
Do not continue driving if the vehicle has reduced or erratic throttle response; it may enter limp mode or fail to accelerate as expected. If the engine runs normally, drive only to a safe location for diagnosis, since disagreement between the redundant throttle signals can lead to loss of usable throttle.
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.