P0122: The throttle position sensor voltage is too low
Throttle/Pedal Position Sensor/Switch A Circuit Low Input
The throttle position sensor signal is too low, so the car may go into limp mode. Get it checked within a few days and stay off highways. If it stops responding to the pedal, pull over.
Stop driving and get help if
- The check engine light is flashing
- The temperature gauge runs high, or you see steam (overheating)
- The car loses power, hesitates badly or stalls
- You smell burning or see smoke
- A brake warning light comes on, or the brakes feel different
Pull over as soon as you can, turn the engine off, and call a tow or roadside help.
What it means
P0122 means the TPS signal voltage is below the minimum the ECM accepts. The most common cause is a failed sensor, a broken wire, or a bad ground in the TPS circuit. On drive-by-wire systems, both TPS sensors inside the throttle body operate inversely: as one goes up, the other goes down. If one drops below its floor, the ECM flags P0122 and may enter limp-home mode, limiting engine speed.
Common causes
- Failed TPS sensor (open or short to ground)An internally failed sensor pulls the output below the acceptable floor voltage.
- Broken or grounded signal wireA wire that has chafed against metal grounds the TPS signal line to zero.
- Corroded or damaged TPS connectorA connector with missing or bent pins breaks the signal path entirely.
- Failed 5V reference supply to the TPSIf the reference voltage is lost, the sensor output is also near zero even if the sensor is good.
What the fix could involve
From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.
- TPS sensor replacement (cable)
- Electronic throttle body replacement
- Wiring repair
Symptoms
- Check engine light on
- Engine stuck at idle or limited RPM (limp mode)
- No throttle response or severely delayed response
- Stalling when trying to accelerate
- Transmission stuck in one gear
What to do next
Check the TPS connector first, since a simple loose connector is the easiest fix. With a multimeter and the ignition on, verify 5V reference voltage at the sensor. If the reference is present but signal stays near zero, the sensor is internally shorted or the signal wire is grounded. Replace the sensor if wiring checks out clean. On drive-by-wire throttles, the sensor cannot be replaced separately from the throttle body on most vehicles.
Lewis shows the live throttle position reading alongside any related throttle sensor codes, so you can see whether the signal is reading low. Get Lewis on the App Store or Google Play.
Related codes
FAQ
- Will P0122 put my car in limp mode?
- Yes, on most vehicles. The ECM treats a TPS signal below minimum as a safety fault and limits engine power or speed to protect the drivetrain from unexpected commands.
- Can the accelerator pedal sensor cause P0122 instead of the throttle body sensor?
- Yes. Some vehicles use a separate accelerator pedal position sensor, which has its own codes (P0222, P0223). But P0122 specifically targets the throttle body TPS circuit.
- How long can I drive with P0122?
- Get it checked within a few days. Once the engine enters limp mode, stay off highways: limp mode limits RPM and may restrict shifting. If the car will not accelerate, pull over and have it towed.
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