AutoDiag

P0122

Throttle/Pedal Position Sensor/Switch "A" Circuit Low

High· Fix promptlyIntermediatePowertrainGeneric, all makes

What it means

The throttle position sensor A (TPS A) signal voltage is below the normal range. The throttle position sensor A (TPS A) tells the ECU how far open the throttle plate is. A low signal is usually caused by a short to ground, a missing reference voltage or a failed sensor.

Is it safe to drive?

Drive with caution. On electronic throttle cars the ECU may cut power to a "limp mode", which makes merging and overtaking dangerous.

Symptoms

  • Check engine light on
  • Hesitation or flat spots on acceleration
  • High or unstable idle
  • Reduced engine power or "limp mode" on drive-by-wire cars
  • Harsh or erratic automatic transmission shifts

Probable causes

Most likely first

  1. 1Open or shorted 5-volt reference wire from the ECU
  2. 2Signal wire shorted to ground
  3. 3Unplugged, corroded or loose connector
  4. 4Failed sensor
  5. 5Another sensor on the same 5V reference circuit shorting it down

How to diagnose it

Work through these in order before buying parts

  1. 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
  2. 2Inspect the throttle position sensor A (TPS A) connector and wiring (on the side of the throttle body). Look for corrosion, bent or pushed-back pins, oil contamination and chafed insulation.
  3. 3Watch the throttle position sensor A (TPS A) reading on live data. Reading should rise smoothly from about 0.5 V (closed) to about 4.5 V (wide open) with no jumps or dropouts as you press the pedal (key on, engine off).
  4. 4With the key on and the sensor unplugged, check for about 5 volts on the reference wire and a good ground (under 0.1 V drop) on the ground wire. Back-probe the signal wire with the sensor connected and watch the voltage change smoothly.
  5. 5If the wiring checks out, test the sensor itself against the specification in a service manual.
  6. 6Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

  • Repair the damaged wiring or connector
  • Replace the throttle position sensor A (TPS A)
  • Clear the code and test drive to confirm the repair

This information is general guidance for all makes. Exact causes, specifications and procedures vary by vehicle, so confirm with your service manual or a qualified mechanic before replacing parts.