Understanding P0123: Throttle Position Sensor/Switch A Circuit High Input

Introduction to P0123 Code

The P0123 code is a standard OBD-II trouble code that triggers when the Engine Control Module (ECM) detects a higher than normal voltage input from the Throttle Position Sensor (TPS).

Understanding the Throttle Position Sensor

How does the Throttle Position Sensor work?

The Throttle Position Sensor is a key component that signals the ECM about the position of the throttle. It works in sync with the throttle body, a part of the air intake system, to control the amount of air entering the engine.

The role of the Throttle Position Sensor in a vehicle

The TPS plays a crucial role in ensuring the engine runs smoothly. It helps manage fuel efficiency, emission control, and overall engine performance.

Symptoms of a P0123 Code

Poor fuel economy

One of the first signs of a P0123 code is decreased fuel economy. The TPS’s improper reading may lead the engine to consume more fuel than necessary.

car vertical

Engine misfires

A faulty TPS can also cause engine misfires. Since the sensor can’t relay the correct throttle position, the ECM struggles to regulate the air-fuel mixture, causing misfires.

Difficulty in acceleration

Difficulty or delay in acceleration is another symptom. The throttle body may not get the right signals, affecting your car’s acceleration.

Causes of a P0123 Code

A P0123 code can be caused by several factors, including a faulty TPS, corroded connector terminals, or a shorted wiring harness.

How to diagnose and fix a P0123 Code

Tools needed

Before you start, you’ll need a multimeter, an OBD-II scanner, and a repair manual for your specific vehicle.

Step-by-step diagnostic process

The first step in diagnosing a P0123 code is to scan the vehicle with the OBD-II scanner. Following the diagnostic steps detailed in your repair manual can help you pinpoint the issue.

Possible solutions

Solutions may range from replacing the TPS, cleaning the connector terminals, to repairing the wiring harness.

Preventing P0123 and other OBD-II codes

Regular maintenance of your vehicle is crucial to prevent not only a P0123 code but also other potential OBD-II codes. This includes timely replacement of the TPS, regular checkup of the wiring, and keeping the connector terminals clean.


Dealing with a P0123 code can be challenging, but understanding its causes and symptoms can help you diagnose and fix the issue. Regular maintenance, including checking the TPS and associated wiring, can prevent this and other similar codes. Remember, if you’re not confident in diagnosing or fixing the problem, it’s always best to seek help from a professional mechanic.

Frequently Asked Questions

Q1: Can I drive my car with a P0123 code?

Yes, but it’s not recommended. The car may experience performance issues such as poor fuel economy and acceleration problems.

Q2: How much does it cost to replace a Throttle Position Sensor?

The cost can vary based on the model of your vehicle and the mechanic’s charges, but it typically ranges from $100 to $200.

Q3: Can a bad Throttle Position Sensor cause transmission problems?

Yes, a faulty TPS can cause irregular shifting patterns or even transmission failure in severe cases.

Q4: How often should I replace the Throttle Position Sensor?

There’s no specific replacement interval for the TPS. It’s advisable to replace it when you experience symptoms of a faulty TPS or when an OBD-II code indicates a TPS problem.

Q5: What other problems can a faulty Throttle Position Sensor cause?

A faulty TPS can lead to several issues, including stalling, rough idling, engine misfires, and even check engine light activation.