Bad throttle position sensor symptoms – P0121 P0122

Introduction

In this tutorial, we will explore the symptoms and diagnostic process related to a bad throttle position sensor (TPS) in vehicles. A faulty TPS can lead to issues such as limp mode, rough idling, and the persistent illumination of the engine management light. We will guide you through identifying the symptoms, testing the TPS using a multimeter, and understanding the relevant fault codes.

Step 1: Identify Bad Throttle Position Sensor Symptoms

Before testing the TPS, it's essential to recognize the symptoms that indicate it may be malfunctioning. Common signs include:

• Limp mode activation
• Rough or unstable idling
• Poor acceleration or throttle response
• Engine management light illuminated on the dashboard
• Inconsistent engine performance

Be attentive to these symptoms as they can help you determine if the TPS needs further investigation.

Step 2: Understand Relevant Fault Codes

Familiarize yourself with the fault codes associated with TPS issues. The codes to watch for include:

• P0120: Throttle/Pedal Position Sensor A Circuit Malfunction
• P0121: Throttle/Pedal Position Sensor A Circuit Range/Performance Problem
• P0122: Throttle/Pedal Position Sensor A Circuit Low Input
• P0123: Throttle/Pedal Position Sensor A Circuit High Input

These codes can be retrieved using an OBD-II scanner and will provide insight into the specific nature of the problem.

Step 3: Testing the Throttle Position Sensor with a Multimeter

To accurately diagnose a faulty TPS, follow these steps to test it with a multimeter:

1. Gather Required Tools

   • Multimeter
   • Vehicle service manual (for wiring diagrams)

2. Locate the TPS

   • Find the throttle position sensor on the throttle body of your vehicle.

3. Disconnect the TPS Connector

   • Carefully unplug the electrical connector from the TPS.

4. Set Up the Multimeter

   • Turn on the multimeter and set it to measure voltage.

5. Test the Voltage Output

   Connect the multimeter probes to the appropriate pins on the TPS connector

   • Reference voltage pin (usually powered by the vehicle's battery)
   • Signal output pin (this is where the TPS sends its position signal)
   • With the ignition on (engine off), check for the reference voltage (typically around 5 volts).

6. Test the Sensor's Functionality

   • Slowly open the throttle plate and observe the voltage change on the multimeter. The output voltage should vary smoothly as you open and close the throttle.
   • If the voltage does not change or shows erratic readings, the TPS may be faulty.

Step 4: Addressing a Faulty Throttle Position Sensor

If testing reveals that the TPS is indeed malfunctioning, consider the following options:

• Replacement: If the TPS is faulty, replacing it with a new or remanufactured unit is often the best course of action.
• Check Wiring and Connections: Inspect the wiring and connectors for any signs of damage or corrosion, as these can also lead to sensor issues.
• Professional Assistance: If you are unsure or uncomfortable with testing, seek help from a qualified mechanic.

Conclusion

A faulty throttle position sensor can significantly affect your vehicle's performance. By identifying the symptoms, understanding fault codes, and testing the TPS with a multimeter, you can diagnose the issue effectively. If you determine the TPS is bad, consider replacing it and checking for any underlying wiring issues. Regular maintenance and prompt diagnosis can help ensure your vehicle runs smoothly. For further assistance, explore professional services for TPS replacement or remanufacturing.