P0123 Code – Meaning, Symptoms, Causes (& How To Fix)

P0123 - Throttle Position Sensor/Switch A Circuit High Input

P0123 Code

When the Check Engine Light comes on and the vehicle goes into a failsafe mode, you might find yourself dealing with the P0123 trouble code. While it is a generic powertrain code, there’s a lot you can learn through diagnosis.

In this article, we focus on the P0123 meaning. We also look at what might cause it, the symptoms it creates and show you ways to resolve the problem once and for all. 

Code P0123 Definition

P0123 – Throttle Position Sensor/Switch A Circuit High Input

What Does the P0123 Code Mean?

The P0123 code indicates that the engine control module received a high input signal from the throttle position sensor A. The throttle position sensor A is a three-terminal resistor mounted to the throttle body and shaft, determining valve position.

It evaluates the throttle blade angle and sends data back to the throttle actuator module or PCM (powertrain control module). If the signal doesn’t respond properly, the P0123 code gets set. 

If your vehicle contains electronic traction control, there will also be two accelerator pedal position (APP) sensors that measure the angle of the gas pedal. If there’s a problem with the APP sensors, this code could also be set. 

RELATED: 5 Signs of a Bad Throttle Position Sensor (Replacement Cost)

P0123 Trouble Code Symptoms

The most common symptom is the Check Engine Light. However, the car is also going to enter its failsafe mode to prevent the engine from any damage.

Here are a few things you might notice:

  • Check Engine Light
  • Engine in failsafe mode, with reduced throttle
  • Higher than normal idle
  • Lack of acceleration
  • Rough idle

Causes of the P0123 Code

There are numerous causes to the P0123 code. Most of the issues have to do with either the throttle position sensor or the throttle body.

Here are some issues that could cause the P0123 code:

  • Malfunctioning throttle position sensor
  • Bad pedal position sensor
  • Sensor circuit issues, including loose connections, wiring or short circuits
  • Contaminated or bad throttle body
  • PCM needs update

How Serious is the P0123 Code?

High – When P0123 occurs, the ECM goes into a failsafe mode to protect the engine and transmission from damage. Until you have the issue repaired, you are going to have trouble getting the car to accelerate or go over a certain speed.

Failsafe mode is only intended to help you get home and avoid being stranded. It’s very difficult to drive long distances because the car may exhibit a high idle, stalling, bucking and jerking along the way. Get the car home or to your mechanic right away for repair. 

What Repairs Can Fix the P0123 Code?

There are several repairs that could fix the P0123 trouble code. However, a proper diagnosis should always be performed before you start throwing money at parts. 

Here are a few of the most common repairs:

Common P0123 Diagnosis Mistakes

The most common mistake when diagnosing the P0123 code is replacing major components before performing a complete diagnosis. For example, you might replace the throttle or pedal position sensor when the issue was just a poor connection or faulty wiring. 

You could also replace the throttle position sensor or switch when you only needed to clean out the contaminated throttle body. There’s also the chance that you replaced the pedal position sensor only to find out that something simple was messing with the angle, such as damaged floor mats. 

Recommended Tools for Diagnosis

How to Diagnose the P0123 Trouble Code

Here are the steps that a professional would take while diagnosing the P0123 code.

  1. Use your engine code scanner with freeze frame data to see what’s happening with the car. Clean all of the fault codes and retest the vehicle to see what comes back. 
  2. Clean the carbon out of the throttle body with specialized cleaning agents. 
  3. Review any technical service bulletins (TSB) that might correspond to your issue. If the manufacturer has talked about the same thing, you can save yourself a lot of time. 
  4. Examine the TPS wiring and connections for any damage or shorts. Repair any wiring issues before proceeding.
  5. Perform a pinpoint test between TPS circuits A and B, as laid out by the manufacturer in the service manual. Replace the TPS if needed and clear the codes. 

Estimated Cost of Repair

Here’s an example of what you might spend to perform the necessary repairs.

  • Replace TPS connector – $15-$75
  • Repair wiring short – $15-$500
  • Replace TPS sensor – $100-$300
  • Clean/Replace throttle body – $10-$650

Mechanics Tips about the P0123 Code

It’s not uncommon for the P0123 code to show up with other trouble codes. With the help of manufacturer pinpoint tests, you will be better equipped to find the problem. 

All TPS codes are designed to put the ECM into a fail-safe mode. No matter what is causing this issue, the drive symptoms will be exhibited until a repair is made. 

Magnus Sellén
Written by:

Magnus is the owner and main author of Mechanicbase. He has been working as a car mechanic for over 10 years, and the majority of them specialized in advanced car diagnostics and troubleshooting. Certified Automotive Diagnostic Technician.

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