What P0122 means
Your car has a throttle position sensor (or on newer cars, a pedal position sensor) that tells the engine computer how far the throttle is open or how far you're pressing the gas pedal. P0122 means the computer is seeing a voltage signal from that sensor that's lower than it should ever be, low enough that the computer treats it as impossible. It's not measuring "the throttle is closed" — it's saying "something is wrong with this reading."
Is it safe to drive
Treat this one seriously. When the computer can't trust the throttle signal, most cars pull back power and go into a "limp mode" — reduced RPM, sluggish acceleration, sometimes stuck in one gear. That's the computer protecting itself, not the car falling apart. But some vehicles handle a bad throttle signal worse than others, with hesitation or a stall at idle or at stops. If the car is drivable but feels off, get it looked at in the next few days rather than driving on it for weeks. If you get sudden stalling, hard hesitation in traffic, or the pedal feels disconnected from engine response, don't push it — have it looked at right away.
Common causes, most likely first
The throttle or pedal position sensor itself failing is common, but it's not the only cause, and not always the first thing to check:
- Wiring problems — a chafed wire, corroded connector, or loose ground near the throttle body or under the dash by the pedal. Very common, and cheaper to fix than a sensor.
- The sensor itself worn out or with a bad internal connection.
- On throttle-body-mounted sensors, a dirty or damaged throttle body affecting the sensor's seating or movement.
- On drive-by-wire cars (most since the mid-2000s), the pedal assembly itself, which houses its own sensor.
- Less often, a problem with the engine computer's power or ground supply to the sensor circuit.
Which of these applies depends a lot on the engine and whether the car uses a cable throttle or electronic throttle control. We wouldn't guess without looking.
What diagnosis and repair involves
Diagnosis means checking the actual voltage at the sensor and back through the wiring with a meter or scope, not just reading the code and swapping parts. That usually takes under an hour of shop time. If it turns out to be a wiring or connector issue, repair can be inexpensive. If the sensor or the whole throttle body/pedal assembly needs replacing, cost varies quite a bit by make and model — some are simple bolt-on sensors, others require the whole throttle body or pedal unit as an assembly, which runs more. We wouldn't want to quote a number without knowing which one it is.
Nick Porter handles driveability and diagnostic work at Auto Star Service Center in Graham. We're open Saturdays, 8 to 6, if weekday time is hard to find. Call (253) 375-7057 to get it on the schedule.