P2135: Throttle/Pedal Position Sensor/Switch "A"/"B" Voltage Correlation

What does P2135 mean?

Electronic throttle systems use two sensor signals for the throttle and often two for the pedal, so the ECM can cross check them. When the "A" and "B" signals do not correlate, the ECM cannot trust the reading and usually limits throttle opening.

Both references list the throttle position sensor, the accelerator pedal sensor and the wiring between them and the ECM as common causes. A failed ECM is possible but less common.

Common symptoms

• Check engine light on
• Reduced power or limp mode
• Hesitation or surging on acceleration
• High or unstable idle
• Stalling in some cases

Common causes

The causes below are the ones commonly seen with P2135. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

• A faulty throttle position sensor (often part of the throttle body)
• A faulty accelerator pedal position sensor or pedal assembly
• Wiring or connector problems such as corrosion, opens or shorts
• A faulty ECM or PCM (less common)

What to check with a scanner

• In Live data, compare the two throttle or pedal position values while slowly pressing the pedal. They should move smoothly and stay in step.
• Wiggle the harness gently near the throttle body and pedal while watching the values for dropouts.
• Note companion codes such as P0122, P0123 or other throttle codes.
• Clear the code and see whether it returns.

How to read and clear P2135 with OBD Master Pro

1. Plug in your adapter. Connect a generic ELM327 (or ELM329) OBD2 adapter to the diagnostic port, usually under the dashboard on the driver's side. Bluetooth Classic, Bluetooth LE, Wi-Fi and USB OTG adapters are supported.
2. Switch the ignition on. Turn the key to ON or start the engine, depending on your car.
3. Connect in OBD Master Pro. Open the app, go to Connection and pick your adapter. Classic Bluetooth adapters connect from the Bluetooth tab, Bluetooth LE adapters from the BLE tab with no pairing needed. Use the generic OBD2 / EOBD profile or your car's brand profile.
4. Read the codes. Open the fault codes screen to see stored, pending and permanent codes. Confirm P2135 is listed and note any other codes, since they often explain the cause.
5. Check the details. Look at freeze frame data, Live data and, where your car supports it, Mode 06 test results (see the checks above).
6. Fix, then clear. After the repair, clear the codes to turn off the check engine light. Clearing also resets the emissions readiness monitors, so drive normally and check the readiness screen before any inspection. Permanent codes cannot be erased with a scan tool; they clear on their own once the car's self test passes.

Tip: you can also look up P2135 and other codes in the app's DTC search without connecting to a car. If your adapter will not connect, use Connection > Share connection log and email it to support. Many cheap ELM327 clones only handle basic engine OBD2, which is all you need for P2135.

When to see a mechanic

Get professional help if any of these apply:

• The car is in limp mode
• The engine revs without pedal input
• The throttle body or pedal needs replacing and relearning

If you are unsure, a qualified technician can confirm the cause with tests such as smoke testing, pressure testing or scope readings. Clearing a code does not repair the fault.

Related trouble codes

See all OBD2 trouble code guides

Related guides

Check engine light on: what to do · How to read an OBD2 code (P, B, C, U) · Stored, pending and permanent codes and freeze frame · OBD2 readiness monitors explained · OBD2 glossary · OBD2 by car brand