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

What is P0123?

Diagnostic trouble code P0123 is defined as ‘Throttle Position Sensor/Switch A Circuit High Input.’ It’s a generic powertrain code that applies to all OBD-II equipped vehicles manufactured after 1996. 

The Throttle Position Sensor (TPS) is a device that measures how much the car’s throttle is open. The throttle is a valve that controls how much air enters the engine, which affects engine speed and power. The TPS acts like a variable resistor, changing its resistance based on the position of the throttle.

The TPS is attached to the throttle body and is powered by a 5-volt signal from the car’s Engine Control Module (ECM) or Powertrain Control Module (PCM). Based on the throttle’s position, the sensor sends back a voltage through a signal wire.

This signal helps the ECM or PCM decide how much fuel to inject and when to adjust the ignition timing. When the throttle is fully open, the signal is usually around 4.5 volts. 

DTC P0123 occurs when the control module records an output voltage higher than the normal upper limit (4.5V) for over 2 seconds.

NOTE: If your car has Electronic Throttle Control (ETC), it uses an accelerator pedal position sensor on the gas pedal to measure how far you’re pressing it. In this case, the P0123 code can occur if there’s a problem with the accelerator pedal position sensor instead of the throttle sensor.

Some other TPS codes that can occur alongside P0123 include:

• P0121: TP Sensor “A” Circuit Range Performance Problem
• P0122: TP Sensor/Switch A Circuit Low Input

What Are the Causes of a P0123 Fault Code?

Several issues can trigger DTC P0123, such as:

1. A faulty TPS that sends incorrect voltage to the ECM or PCM
2. Damaged wiring or loose connections between the throttle sensor and control module that disrupt signal flow
3. A short circuit, open circuit, or high resistance in the TPS circuit that results in abnormal voltage readings
4. A dirty or sticking throttle plate that interferes with the TPS function and causes false signals
5. A faulty ECM or PCM that misreads the sensor signal and sets the error code (rare)

NOTE: Sometimes, a carbon-clogged throttle valve can interfere with the movement of the throttle shaft, causing the TPS to read an incorrect or inconsistent throttle position. Although less common, this can also trigger DTC P0123.

3 Common Symptoms of Code P0123

If you have an active P0123 error code, you may notice:

1. An illuminated Check Engine Light: This warning light appears on the dashboard when any generic powertrain code is triggered.

2. Issues caused by failsafe mode: As soon as your Engine Control Module detects a problem, it goes into a failsafe mode to prevent further damage. The failsafe mode causes drivability issues, such as:
   • Erratic acceleration when pressing the gas pedal due to incorrect throttle input.
   • A noticeable lag or hesitation between pressing the pedal and the engine’s response.
   • Engine stalling or idle issues
3. Increased fuel consumption: A faulty throttle sensor can send incorrect signals to the ECM, causing the engine to run too rich or lean. This leads to inefficient fuel use and higher fuel consumption. 

Can You Still Drive with a P0123 Error Code?

Driving with a P0123 trouble code isn’t recommended as it can cause unpredictable throttle behavior, such as sudden acceleration and poor response. These issues can make driving unsafe, especially in traffic or high-speed situations. 

It’s best to consult a mechanic to diagnose and repair the underlying issue immediately.

How to Diagnose Error Code P0123: A General Know-How

It’s essential to have a qualified mechanic diagnose and repair the TPS codes rather than attempting a DIY fix. 

Modern OBD-II equipped vehicles are complex, and incorrect troubleshooting can lead to misdiagnosis, unnecessary part replacements, or further damage. Professionals use advanced car diagnostic tools that provide accurate data and insights, making it easier to pinpoint and fix the exact issue.

Here’s how a technician will proceed:

1. The mechanic will first connect an OBD-II scan tool to retrieve the P0123 code and examine freeze frame data. This helps determine the conditions under which the code was set, such as engine load, throttle position, vehicle speed, and RPM.

2. Using the scan tool and with the engine on, the mechanic will review the throttle TPS data in real-time. They may compare readings from TPS circuit A and B (if applicable) to identify inconsistencies or abnormal voltages.

3. With the ignition on (engine off), they’ll test the TPS signal voltage using a multimeter. A typical TPS receives a 5-volt reference from the ECM or PCM. Readings higher than the normal upper limit may indicate a sensor problem, open circuit, or wiring issue.

4. The mechanic will visually inspect the TPS wiring harness and TPS connector for signs of damage, corrosion, loose pins, or wear. They’ll clean or repair any component as needed.

5. If they find irregular voltage readings, they’ll conduct TPS pinpoint tests as mentioned in your vehicle’s service manual to confirm a faulty TPS.

6. Finally, the mechanic may inspect the electrical terminals and connections between the PCM and the throttle body. They’ll ensure there are no loose, corroded, or damaged terminals that could affect signal integrity or continuity.

Possible Repairs & Costs for P0123 Trouble Code

The repair costs for a P0123 error code can vary depending on the root cause or underlying issue identified during diagnosis.

Here are the estimated costs (including labor) for addressing P0123 issues:

• TPS replacement: $150 to $710
• Throttle body cleaning: $170 to $300
• Throttle body replacement: $520 and $710

What Are Some Common Misdiagnoses Associated with Code P0123?

Common mistakes that can be made while diagnosing and fixing a P0123 fault code include:

• Replacing the throttle or pedal position sensor when the underlying issue is a poor electrical connection or damaged wiring.

• Replacing the TP sensor when the problem is a dirty or carbon-clogged throttle body.

• Replacing the pedal position sensor when the issue is caused by torn or obstructive floor mats interfering with pedal movement.

8 Essential Tips to Prevent the Diagnostic Trouble Code P0123

Here’s what you can do to prevent triggering a DTC P0123:

1. Follow the manufacturer’s recommended maintenance schedule to ensure the throttle system remains in good working order.

2. Have your mechanic scan for trouble codes using car diagnostic tools to catch potential issues during scheduled maintenance.

3. Get your throttle body cleaned during routine servicing to prevent carbon buildup.

4. Ask your mechanic to visually inspect the TPS wiring harness to identify and fix any damage or loose connections.

5. Use high-quality fuel to reduce carbon deposits that can interfere with sensor performance.

6. Drive smoothly and avoid sudden acceleration or braking to reduce wear on throttle components.

7. Purchase genuine or high-quality replacement parts when repairing components like the TP sensor or wiring.

8. Consult experienced technicians to ensure proper installation and long-term performance.