P0122 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

Throttle Pedal Position Sensor/Switch (TPS) A Circuit Low Input

Meaning

Pulling a P0122 trouble code on your OBDII scanner occurs when the Engine Control Module (ECM) registers a reading below 2 volts from Throttle Pedal Position Sensor/Switch (TPS).

Causes

The primary cause of the code is a reading under 2 volts from the A sensor via the ECM. As to the root cause, it’s usually one of the following:

  • loose, broken or corroded TPS sensor wiring
  • loose, broken or corroded TPS sensor wiring connectors
  • a damaged or worn out TPS sensor

Symptoms

Here’s what the typical driver experiences when a vehicle registers a P0122 trouble code:

  • The ECM illuminates the Check Engine Light on and switches the throttle module into failsafe mode. Failsafe mode cuts the current to the throttle actuator,  effectively locking the throttle valve to approximately a 6 degree open position
  • .The ECM makes the necessary adjustments to the fuel injectors and engine timing to limit/control engine speeds.
  • Once in failsafe mode, your vehicle will only drive at slow speeds with limited throttle response.
  • These symptoms may be accompanied by higher than normal engine idle and loss of acceleration power even before the ECM engages failsafe mode.

Diagnosis

You’re probably okay completing this as a DIY replacement job provided you follow a straightforward, step-by-step diagnosis process. Here’s our recommended method:

  • Begin by scanning and documenting all codes received, then view the freeze-frame data to verify when the ECM set the code. This may give insight into the root cause of the error code.
  • Next, clear all OBD-II fault codes and retest the vehicle to see if the P0122 comes back.
  • If your vehicle is still coding P0122, visually inspect all the TPS connections for damage or corrosion. Make sure all connectors are secure, too.
  • Next, compares data between TPS circuit A and B on the scanner. If the readings are incorrect, you’ll need to perform the manufacturer recommended TPS pinpoint tests. These can be simple or complex depending on the make, model and year of your vehicle.
  • Finally, replace the TPS if necessary, then clear the codes and perform a road test.

Common mistakes

Here are some common diagnostic mistakes to avoid when trying to resolve a P0122 trouble code:

  • Failing to complete a thorough visual inspection of connectors and wiring first (this is the number one cause of unnecessary repairs)
  • Failing to scan, document, clear and retest all OBDII codes to verify TPS failure
  • Replacing the TPS sensor without verifying it's actually the problem
  • Failing to compare the TPS sensor A and B data with manufacturer specification before and after repair or replacement.

How serious is this?

As far as drivability is concerned, a P0122 code immediately puts you ECM into failsafe mode. Acceleration will be impeded and the engine may feel “stuck” in high idle. You may also experience bucking or jerking when attempting to accelerate, limited speeds no matter how much you push the accelerator down and engine stalling depending on how your make and model car’s ECM handles failsafe mode.

What repairs can fix the code?

Fixing the problem behind a P0122 is generally a quick and easy fix provided you have properly diagnosed the root cause. Here are the typical repairs you can expect:

  • Repairing or replacing the TPS connectors
  • Repairing or replacing sensor wiring as necessary
  • Replacing the TPS with a new sensor (the cost is determined by make and model)

Related codes

None listed.

Conclusion

When your vehicle codes P0122, it’s generally a good news/bad news scenario. There are few causes responsible for this code, so diagnosis is a great deal less complicated than most OBDII trouble code resolutions. Conversely, depending on your vehicle, accessing the wiring and sensor may be a complex process. If you aren’t comfortable with DIY automotive repair or if you don’t have much experience working with automotive electronics, you may want to get your car in the shop as soon as possible.

Most of the time your vehicle should be drivable enough to get it to the nearest repair shop even in failsafe mode. However, don’t hesitate to have it towed if you are concerned about road safety. “The Little Engine That Could” mentality does put you and other drivers on the road at risk. It’s also not recommended that you attempt to drive a vehicle in failsafe mode on major roads or highways since many times you cannot accelerate or achieve the minimum speed limit. All in all, this is a correctable issue provided you get it to a shop in a timely manner.