Code 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.”

It means the throttle position sensor (TPS) has reported a voltage that’s too low, suggesting a fault in the sensor or its circuit.

The TPS informs the engine control module (ECM) how far the throttle valve is open based on how much you’ve pressed the gas pedal. It does this by sending the appropriate voltage signal in response to your pedal input, from idle (closed throttle valve) to wide open throttle (WOT).

The normal range of this voltage is between 0.5V and 4.5V.

The ECM watches this voltage closely. If the signal drops too low — lower than the specified range limit — the system triggers the DTC P0122.

8 Telltale Symptoms of a P0122 Error Code

A P0122 code can manifest as:

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 or rough idling: 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 may open too slowly or not enough, leading to sluggish acceleration.

5. Reduced engine power: The engine may feel weak or slow to respond. This is because the car enters a limp or failsafe 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.

What Are Some Common Causes of a P0122 Code?

Probable causes that can lead to a fault code P0122 are:

• 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. 

• Damaged TPS connector or wiring: One of the common causes of a P0122 code is a worn-out TPS connector or damaged wiring that interrupts the sensor signal to the ECM. Such loose connections may 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: When the pedal position sensor malfunctions, it sends inaccurate signals that can mimic a faulty TPS and trigger a low input warning. A poor connection or damage in the wiring 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.

Can You Still Drive with a P0122 Fault Code?

Car care experts don’t recommend driving with this error code.

When the P0122 code activates, some vehicles may enter limp or failsafe mode, limiting throttle response, reducing power, or even causing stalling. These symptoms can make driving unsafe and unpredictable.

If you notice hesitation, poor acceleration, 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

Resolving this code involves checking electrical components and precise voltage measurement. The lack of a proper scan tool or technical expertise can lead to misdiagnosis and further damage.

So, if you suspect a P0122 error code, you should always take your car to a qualified mechanic for diagnosis and repair. 

Here’s how a mechanic will typically troubleshoot the probable causes of a DTC P0122 and address them:

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. The voltage output should increase smoothly with the throttle opening angle. Any irregularities in the voltage output 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, like floor mats or debris blocking the gas pedal and affecting the sensor’s operation. The mechanic will clean the area and secure the mat properly.

8. Inspect related components like the throttle body and clean them up.

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 of fixing a fault code P0122 usually ranges between $50 and $1,500. The exact amount depends on the possible causes triggering the code and the parts that need repair.

Here are the estimated costs (including labor charges) for common components involved:

• Accelerator pedal position sensor replacement: $50 to $250
• TPS replacement: $150 to $710
• Throttle body replacement: $520 to $710
• ECM replacement: $800 to $1,500

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

Here are some tips to prevent a diagnostic trouble code P0122:

• 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 75,000 miles to prevent carbon buildup around the TPS.