P2135: Throttle/Pedal Position Sensor/Switch A/B Voltage Correlation
Do not keep driving
The car will be in reduced power or refusing to rev. Before agreeing to a throttle body or pedal assembly — neither is cheap — ask whether the five-volt reference and the ground were measured at the connector. Both sensors share those, so one bad supply makes two good sensors disagree, and that is a much smaller repair. If other unrelated sensors are also faulted, that points the same way.
What this code means
Position sensors A and B disagree. This is the code the whole redundancy arrangement exists to produce, and it is among the most commonly misdiagnosed in the P2 range — because the obvious reading of it is wrong more often than it is right.
What it means. Sensors A and B are the deliberately-mismatched pair described under P2104: different slopes, or one rising while the other falls, so that no single fault can move both in a way that still looks consistent. The module compares them continuously. When they disagree beyond tolerance, it knows one of them is lying and — critically — it cannot tell which. So it distrusts both and withdraws throttle authority, which is why P2104 or P2106 usually appears alongside.
Why the obvious reading is wrong. "The sensors disagree, so a sensor is faulty" skips the thing they have in common. Both are fed from the same five-volt reference and share a ground, usually through the same connector. If that reference sags, or the ground develops resistance, both sensors shift at once — and because they have different slopes, they shift by different amounts. The correlation fails. Neither sensor is faulty. The corpus makes this argument at length under P0641 and it applies here exactly.
Why it matters financially. On a throttle body, the two sensors are integral and not separately available, so "replace the sensor" means replacing the whole throttle body. On a pedal, the same is true of the pedal assembly. Neither is cheap, and a five-volt reference fault or a corroded shared connector costs a fraction of either.
So the order is: measure the reference voltage and the ground at the connector, check the connector itself, and only then look at the sensors. If other unrelated sensors are also reporting faults, that is the shared-supply case confirming itself and the sensors here are almost certainly innocent.
Likely causes
Start here
- Failed sensor reference voltage supply · moderate
- Corroded or loose connector · easy
- Poor sensor ground connection · moderate
Less common
- Faulty throttle position sensor · moderate
- Faulty accelerator pedal position sensor · easy
- Carbon deposits in the throttle body · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P2135.