OBD-II Code P0122 — What It Means & How to Fix It

What Does This Error Mean?

P0122 means the Throttle Position Sensor (TPS) is sending a voltage that's too low. The TPS tells the engine computer how far open the throttle plate is. A low voltage signal makes the computer think the throttle is almost closed. This causes hesitation, stalling, and poor response when you press the gas. The car may also go into limp mode to protect the engine.

Affected Models

All vehicles 1996+
Common in Ford Ranger
Common in Chevrolet S10
Common in Dodge Dakota
Common in Toyota Tacoma

Common Causes

Worn-out throttle position sensor with internal resistance problems
Corroded or damaged ground wire in the TPS circuit
Loose or disconnected electrical connector at the TPS
Short to ground in the TPS signal wire
Failed accelerator pedal position sensor on electronic throttle systems

How to Fix It

Find the throttle position sensor on the throttle body. It's mounted on the side of the throttle body and has an electrical connector with two or three wires.

On vehicles with electronic throttle control, the TPS is built into the throttle body and can't be replaced separately.
Unplug the connector and inspect it for corrosion, green buildup, or bent pins. Clean all contacts with electrical contact cleaner. Check that the connector locks firmly when reconnected.

Wiggle the connector while the engine runs. If the idle changes, the connector is the problem.
Check the wiring harness from the TPS back toward the engine computer. Look for bare wires touching metal parts, which would cause a short to ground and a low voltage reading.

Pay special attention to spots where wires pass near sharp metal edges or hot exhaust components.
Replace the TPS if the wiring and connector look good. Remove the old sensor, install the new one, and make sure the mounting screws are snug but not overtightened.

A TPS costs $15-$60 at most auto parts stores. Some vehicles need the throttle body removed for access.
Clear the code and perform a throttle relearn if your vehicle requires one. Some cars need you to cycle the key on and off, then slowly press and release the gas pedal several times.

Search for your specific vehicle's throttle relearn procedure online. Getting this wrong can cause high idle.

When to Call a Professional

If a new TPS doesn't fix the low voltage reading, see a mechanic. Wiring shorts to ground require a multimeter and wiring diagram to trace. Electronic throttle body systems may need scan tool calibration. Diagnosis costs about $80-$150. Repairs range from $100 for a sensor to $400 for a throttle body assembly.

Frequently Asked Questions

Why does my car go into limp mode with P0122?

Limp mode activates when the computer can't trust the throttle sensor. Since it doesn't know how much throttle you're requesting, it plays it safe. The computer limits power and speed to prevent uncontrolled acceleration. Your car may feel like it barely moves and won't go above 25-40 mph. Fixing the TPS returns the car to normal operation.

Can a dirty throttle body cause P0122?

Not directly, but indirectly yes. Carbon buildup can prevent the throttle plate from closing fully. This can stress the TPS and cause premature wear. Cleaning the throttle body regularly helps prevent sensor problems. If you're replacing the TPS, clean the throttle body at the same time.

What voltage should the TPS read?

At idle with the throttle closed, TPS voltage should be about 0.5 to 1.0 volts. At wide open throttle, it should read about 4.0 to 4.5 volts. P0122 means the voltage is dropping below the expected minimum. A scan tool with live data can show you the real-time TPS voltage. If it drops below 0.2 volts at any point, the sensor or wiring is faulty.