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

What the P2135 code means

On a vehicle with an electronic accelerator there is no cable between the pedal and the throttle. There are sensors and a motor. Because a fault in that chain could cause unintended acceleration, the system is designed with redundancy. Both the pedal and the throttle body carry two independent sensors, not one.

Those two signals move in step but are not identical. In most systems one rises while the other falls, or one climbs at twice the slope of the other. What matters is that their relationship is always the same, because that is how the computer verifies that both are telling the truth. If one drifts, the other gives it away.

The P2135 code is stored when that relationship breaks. Both signals exist, but they no longer agree, and the system has no way to know which of the two is correct.

Faced with that doubt, the computer applies the only safe strategy: it ignores both, closes the throttle to a minimal opening and limits the engine to a low speed. That is why the symptom is so dramatic, a vehicle that barely moves, even though the cause is often something as simple as dirt or a loose pin.

P2135 code symptoms

• Limp mode with very limited power, often with the engine not going past 1,500 or 2,000 rpm.
• Check engine light on, and on many vehicles the electronic throttle warning symbol as well.
• The engine does not respond to the pedal, or responds late.
• Rough idle, or an engine that stalls when you stop.
• Hard starting.
• The symptom goes away for a while after you shut the engine off and restart it.
• Erratic shifting on automatic transmissions.
• A sudden loss of power while you are driving.

Likely causes of the P2135 code

1. Carbon built up in the throttle body, which keeps the plate from reaching the position the sensor should read. A very frequent cause.
2. Pedal or throttle body connector with backed-out, dirty or wet pins.
3. Pedal sensor with a worn track in the rest zone, which is where it works the most.
4. Electronic throttle body failed internally.
5. Chafed wiring between the pedal and the computer, with one of the two circuits affected.
6. Common sensor ground with high resistance.
7. Five volt reference voltage pulled down by another shorted sensor.
8. Adaptations not reset after cleaning or replacing the throttle body.
9. Weak battery, whose voltage drop briefly throws the readings off.
10. Failed control module. It is the last possibility, never the first.

How to diagnose the P2135 code step by step

1. Watch both signals at the same time in live data while you press the pedal slowly. They should move in step across the whole travel, with no jumps or flat spots. The one that behaves differently is the suspect.
2. Work out whether the problem is in the pedal or in the throttle body. Both carry dual sensors, and the code does not always say which one is failing.
3. Check the five volt reference at both connectors. If it is missing, see whether other sensors are affected too, because that line is often shared.
4. Remove and inspect the throttle body. The carbon around the plate is usually visible to the naked eye and is the most common cause.
5. Inspect the connectors for backed-out pins, green corrosion or moisture, and check that they seat firmly.
6. Wiggle the harness with the key on while watching the readings, to find an internal break in a conductor.
7. Measure the voltage drop on the ground of both sensors.
8. Check the battery condition, because low voltage throws the readings off and sets the code with no real fault.

How to fix the P2135 code

• Clean the throttle body with a product made for it and a soft rag. Do not move the plate by hand and do not force the internal mechanism.
• Reset the throttle adaptations with the scan tool after cleaning. Without this step the idle can end up off and the code can come back.
• Clean the connectors with contact cleaner and apply dielectric grease.
• Replace the pedal sensor if its signal has dead spots or jumps along the travel.
• Replace the complete throttle body when its sensor is built in and not sold separately.
• Repair damaged wiring with solder and heat-shrink tubing, following the original routing.
• Fix the common sensor ground down to bare metal.
• Replace the battery if its voltage falls below the acceptable level during cranking.

After the repair, run the throttle relearn procedure if the vehicle requires it and check that both signals travel their whole range in step with each other.

Technical reference data

• Sensor 1 signal at rest: between 0.5 and 0.9 volts. Wide open: between 3.8 and 4.7 volts.
• Sensor 2 signal: proportional to the first, usually half of its value or inverted, depending on the manufacturer.
• Reference voltage: 5 volts, shared with other sensors in most systems.
• Tolerated deviation between the two signals: around 10 percent before the code is stored.
• Allowable voltage drop on the ground: below 0.2 volts.
• After cleaning or replacing the throttle body, the adaptations must be reset.

Brand-specific notes

The most common mistake with this code is cleaning the throttle body and not resetting the adaptations. The vehicle is left with an off idle and the code returns within a few days, which leads people to replace parts that were in good shape.

Before you order anything, unplug and firmly reconnect both connectors and check the battery condition. Those two checks and the cleaning resolve a very high share of cases.

Frequently asked questions about P2135