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

What it means

Electronic throttle bodies have two position sensors with opposite slopes so the ECM can cross-check them; the two voltages must track within a tight tolerance at every angle. P2135 sets when the correlation is broken, meaning one sensor reads an angle the other does not confirm. Because the ECM can no longer trust the throttle position, it enters limp mode with reduced power.

Symptoms

Sudden loss of power with the engine/EPC lamp on, often while accelerating
Engine stays at idle or limp RPM regardless of pedal position
Intermittent hesitation or jerk before the fault becomes permanent
Stalling when coming to a stop
Fault may clear after a restart and return later

Common causes

Worn potentiometer track in the throttle position sensor (contact-type sensors)
Carbon build-up causing the plate to stick so the two sensors disagree momentarily during movement
Chafed, corroded or water-damaged wiring and connector at the throttle body
Poor shared 5 V reference or sensor ground with voltage drop over 0.1 V
Throttle body motor gears worn, giving backlash between sensors
ECM input fault or missing adaptation after throttle replacement

How to diagnose

Key on, engine off: read TPS1 and TPS2 live. Typical rest values 0.6-0.9 V and 4.1-4.4 V; across the sweep the sum must stay within about 4.8-5.2 V. A deviation beyond 0.1-0.2 V at any angle confirms the correlation fault.
Sweep the throttle with the actuator test while graphing both signals; look for glitches, flat spots or dropouts in one trace, which identify a worn track.
Check the sensor supply: 4.9-5.1 V on the reference pin, ground drop under 0.1 V; wiggle the harness and connector while watching the values for sudden jumps.
Inspect the connector for corrosion, spread terminals and water; many throttle bodies sit under washer reservoirs or in splash zones.
Inspect the throttle plate for carbon; clean if needed, then run the throttle basic setting/adaptation and re-check correlation through the full range.
If wiring, supply and cleaning do not stabilise the signals, replace the throttle body (sensors are usually not separately available) and perform adaptation.

Frequently asked questions

Why does the fault come and go?

A worn sensor track only misreads at certain angles or temperatures. Each key cycle the ECM re-tests; when the plate happens to rest on a good part of the track, the car drives normally until the bad spot is crossed again.

Is P2135 the pedal or the throttle body?

P2135 refers to the throttle body sensors. The accelerator pedal correlation fault is P2138, so the code tells you which component to look at.

Terms to know

Throttle position sensor (TPS)

Throttle/Pedal Position Sensor/Switch 'A'/'B' Voltage Correlation