Skip to content

P2135 – Throttle/Pedal Position Sensor/Switch A / B Voltage Correlation (OBD2)

P2135 means "Throttle/Pedal Position Sensor/Switch A / B Voltage Correlation". Two signals that should agree with each other no longer match. The control unit cannot tell which one is wrong, so it stores a correlation fault for the throttle / pedal position sensor.

Last updated

P2135 quick summary

Fault codeP2135
MeaningThrottle/Pedal Position Sensor/Switch A / B Voltage Correlation
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityHigh
Can I drive?Only carefully. The engine often goes into limp mode with very limited power, which can be dangerous when overtaking or joining a motorway. Have it diagnosed as soon as possible.
Repair cost€30 – €500

How electronic throttle and pedal position sensors work

Throttle and accelerator pedal position sensors tell the engine control unit where the throttle valve and the accelerator pedal are – the basis of electronic throttle control (drive-by-wire).

On modern cars there is no throttle cable. The accelerator pedal has two (sometimes three) position sensors, and the throttle body has its own motor and two position sensors. The control unit compares the driver's request from the pedal with the actual throttle opening hundreds of times per second.

For safety, each position is measured by two independent sensors (A/B, or D/E for the pedal) whose signals must always agree in a fixed relationship – for example one rising while the other falls, or one at half the voltage of the other. If they disagree (P2135, P2138) or one leaves its range, the control unit cannot trust the signal and switches to limp mode: limited throttle opening, raised idle, or no response to the pedal.

Most faults are caused by worn sensor tracks, dirt or carbon in the throttle body, corroded connectors or wiring damage. On older cars with a cable, the throttle position sensor is a simple potentiometer on the throttle body.

Symptoms of P2135

  • Limp mode: very limited power, engine does not rev above about 2,000–3,000 rpm
  • Check Engine and/or EPC light on
  • Delayed or no response to the accelerator pedal
  • Irregular idle or stalling
  • Cruise control not working

Most common causes of P2135 (most likely first)

Mechanic's Pro Tip

Never clean a throttle body and drive off without running the throttle adaptation – the control unit has learned the dirty valve's position and will idle badly or throw new codes. On most cars the adaptation takes a minute with a scan tool and is the most commonly missed step.

  1. 1.One of the two sensors is faulty or drifting

    Most likely

  2. 2.Mechanical cause

    For example a stretched timing chain, a wrong installation or a leak that really makes the two values differ.

  3. 3.Wiring fault on one of the two signals

  4. 4.Dirty or carbon-coated throttle body

    Very common on diesels and direct-injection petrol engines – the valve sticks and the actual position no longer follows the command.

  5. 5.Worn sensor track in the throttle body or pedal

    Potentiometer tracks wear at the most-used positions and cause dropouts.

  6. 6.Corroded or loose connector

    Especially at the throttle body, which is exposed to heat and moisture.

  7. 7.Throttle motor or gearbox failure

    The motor or its plastic gears inside the throttle body wear out.

Step-by-step diagnostic guide

  1. 1

    Read codes and live data

    Read all codes and check whether the fault is on the pedal side (accelerator pedal position sensor) or the throttle side. Look at both sensor values in live data while slowly pressing the pedal.

  2. 2

    Compare both signals side by side

    Display both values together in live data (or on a two-channel oscilloscope) and see which one is out of line with the actual conditions. Fix that signal or the mechanical cause first.

  3. 3

    Check signal agreement

    Both signals must change smoothly without jumps and keep their fixed relationship over the whole travel. A jump or a flat spot at one position means a worn track.

    Multimeter: Typical pedal sensors: signal 1 about 0.5–4.5 V, signal 2 about half of signal 1 or mirrored – check the specification for your vehicle.

  4. 4

    Inspect and clean the throttle body

    With the ignition off, remove the intake hose and inspect the throttle valve. Clean carbon carefully with throttle body cleaner without forcing the valve.

  5. 5

    Check wiring and connectors

    Check the connectors at the pedal and throttle body for corrosion, and the wiring for chafing. Measure the 5 V reference and ground.

  6. 6

    Run the throttle adaptation

    After cleaning or replacing the throttle body or pedal, run the throttle adaptation (basic setting) with a scan tool, otherwise the idle and limp mode problems can continue.

Frequently asked questions

Can I keep driving with P2135?

Only carefully. The engine often goes into limp mode with very limited power, which can be dangerous when overtaking or joining a motorway. Have it diagnosed as soon as possible.

How much does it cost to fix P2135?

Typical repair costs are 30 € – 500 €, depending on the cause and the vehicle. The most common fixes are: one of the two sensors is faulty or drifting; mechanical cause; wiring fault on one of the two signals. Always confirm the cause with the tests above before buying parts.

Why does my car go into limp mode with a throttle code?

Because the throttle controls engine power directly. If the control unit cannot trust the position signals, it limits the throttle opening for safety so that the car cannot accelerate unexpectedly.

Is the pedal sensor or the throttle body faulty?

The code tells you which sensor is involved – pedal codes usually mention 'pedal' or sensors D/E/F, throttle codes sensors A/B/C. Live data showing both signals over the full travel confirms which part is at fault.

What is the difference between P2135 and similar codes?

P2135 belongs to a group of codes for the same component that differ in the type or location of the fault: P2132 – Throttle/Pedal Position Sensor/Switch F Circuit Low; P2133 – Throttle/Pedal Position Sensor/Switch F Circuit High; P2134 – Throttle/Pedal Position Sensor/Switch F Circuit Intermittent; P2136 – Throttle/Pedal Position Sensor/Switch A/C Voltage Correlation; P2137 – Throttle/Pedal Position Sensor/Switch B/C Voltage Correlation; P2138 – Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.