DTC P0122: Throttle Position Sensor/Switch A Circuit Low Input

What Does the P0122 Code Mean?

P0122 is a generic diagnostic trouble code (DTC) defined as “Throttle Position Sensor/Switch (TPS) A Circuit Low Input.”

In simple terms, it indicates that the engine control module (ECM) is receiving a lower-than-expected voltage signal from the throttle position sensor (TPS) or accelerator pedal position sensor.

The throttle position sensor tells your car how far you’re pressing the gas pedal. It does this by sending an electrical signal to the engine computer, which then adjusts engine power, fuel, and acceleration.

Normally, this signal falls within a specified range (0.5V and 4.5V) as you press the pedal. When the signal falls outside the specified range, the engine computer assumes something is wrong (with the sensor or the wiring) and triggers the P0122 code.

8 Telltale Symptoms of a P0122 Error Code

Some typical signs of a P0122 trouble code include:

1. An illuminated check engine light: When the ECM detects a problem with the TPS, it turns on the check engine light as a warning.
2. High idle speed: After startup, the engine may idle at unusually high RPMs (revolutions per minute) when the ECM misreads throttle input.
3. Engine stalling: The engine may run unevenly or shut off unexpectedly, especially at low speeds, due to inconsistent throttle input from the faulty TPS.
   
4. Poor acceleration: You may notice a delay when pressing the gas pedal, as the ECM isn’t receiving the right sensor signal. As a result, the throttle valve and throttle plate may open too slowly or not enough, leading to sluggish acceleration.
5. Reduced engine performance: The engine may feel weak or slow to respond. This is because the car enters a limp mode to prevent damage, limiting throttle response. 
6. Unresponsive or jerky throttle behavior: The gas pedal may feel uneven or cause sudden surges due to weak signals from the throttle sensor. 
7. Hard or delayed transmission shifts: Gear shifts may feel rough or delayed because faulty throttle data disrupts the ECM’s timing.
8. Poor fuel economy: Incorrect throttle data leads to poor air-fuel mixture control and affects fuel efficiency. You may notice fewer miles per tank and more frequent trips to the gas station.

What Are Some Common Causes of a P0122 Code?

Your ECM may detect a P0122 code for the following reasons:

• Faulty throttle position sensor: The TP sensor may wear out or fail over time, sending an incorrect voltage measurement to the ECM.
• Incorrect TPS mounting: If the TPS isn’t properly mounted, it can cause inaccurate voltage readings and throttle response.
• TP sensor wiring or connector damage: One of the most common causes of a P0122 code is TPS wiring harness damage. Any loose connections may also cause a low voltage reading or a short circuit.
• TPS circuit short to ground: When the TPS circuit gets damaged, exposed wires can touch metal parts of the car and create a short to ground. This diverts the electrical signal from the ECM, causing the voltage output to drop below normal levels.
• Pedal position sensor or wiring issues: In vehicles with electronic throttle control, a malfunctioning pedal position sensor can send inaccurate signals that can mimic a faulty TPS and trigger a low input warning. A poor connection or wiring damage can further interfere with the signal, leading the ECM to log a P0122 trouble code.
• Debris blocking the gas pedal: Floor mats or debris stuck under the gas pedal can prevent it from fully engaging. This can interfere with the pedal sensor’s ability to read throttle input correctly.

Faulty ECM: In rare cases, the ECM may have a fault and misinterpret normal voltage signals. This is uncommon and usually diagnosed only after ruling out all other possible causes.

Is it Safe to Drive with a P0122 Fault Code?

We don’t recommend driving with this error code.

When the DTC P0122 activates, your vehicle may enter failsafe or limp mode, limiting throttle response or even causing stalling. These symptoms can make everyday driving — especially merging, turning, or driving in traffic — more difficult and potentially unsafe.

If you notice hesitation, poor engine performance, or rough idling, it’s best to stop driving and take your car to a mechanic.

Continuing to drive with this issue may lead to more serious engine or transmission problems.

How to Diagnose and Fix a P0122 Error Code

Diagnosing a DTC P0122 requires voltage testing, a scan tool, and system calibration. So, it’s best handled by a trained technician rather than attempting a DIY repair.

Here’s how they’ll proceed:

1. Use an OBD-II scan tool to confirm the P0122 trouble code and check for related codes (such as code no. P0120 or P0123).
2. Inspect the TP sensor for visible damage, loose connections, or corrosion. If they find physical defects, they’ll replace the faulty throttle position sensor.
3. Test the TPS voltage and ground signals using a multimeter. If the sensor isn’t receiving proper voltage or ground, the mechanic will trace the issue back through the wiring and connectors for faults or damage.
4. Check the TPS output signal while moving the throttle valve. The output voltage should increase smoothly with the throttle opening angle. Any irregularities in the output voltage mean the sensor is faulty.
5. Examine the pedal position sensor voltage signal to ensure it responds correctly to pedal movement. 
6. Inspect the signal wire or connector in the pedal position sensor circuit, and replace frayed, corroded, or damaged wiring as needed. 
7. Check for physical obstructions, such as floor mats or debris, that may be blocking the gas pedal and affecting the sensor’s operation. The mechanic will clean the area and properly secure the mat.
8. Inspect related components, such as the throttle body and throttle plate, and clean away any carbon buildup that could affect movement or sensor readings. 
9. Test the ECM and replace it if necessary (rare).
10. Clear the code, perform a test drive, and check if any warning lights return to confirm if the issue is resolved.

How Much Does It Cost to Diagnose and Repair Code P0122

The cost to fix a fault code P0122 usually ranges from $60 to $1,500. The exact amount depends on the parts that need repair.

Here are some estimated costs (including both parts and labor):

• Accelerator pedal position sensor replacement: $60 and $870
• TPS replacement: $150 to $710
• Throttle body cleaning: $170 to $300
• ECM replacement: $800 to $1,500

How Can You Prevent TPS Issues and Avoid Triggering the P0122 Code?

Follow these tips to ensure your TPS works optimally:

• Avoid using aftermarket “performance chips” (tools to optimize power and torque systems in a vehicle) that may interfere with the sensor signal.
• Choose high-quality or OEM sensors when replacing the TPS.
• Don’t ignore warning lights — address them early to prevent further damage. 
• Ask a mechanic to clean the throttle body every 25,000 to 90,000 miles (depending on the vehicle and usage) to prevent carbon buildup around the TPS.
• Apply a small amount of dielectric grease to the TPS connector during servicing to prevent moisture and corrosion.
• Keep your air filter clean and properly sealed, and replace it at the manufacturer-recommended intervals (12 months or 12,000 miles).