P0122: Throttle Position Sensor/Switch (TPS) A Circuit Low Input

What is P0122?

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

The throttle position sensor (TPS, TPS sensor, or TP sensor) is connected to the throttle body and monitors your vehicle’s throttle position.

The TPS sensor is a potentiometer that provides a variable resistance depending on the throttle valve opening angle. 

At Wide Open Throttle (WOT), the TPS sensor voltage signal is around 4.5 Volts. The sensor sends this reference voltage to your car’s Powertrain Control Module (PCM) or Engine Control Module (ECM), which then manages the air-fuel ratio and the best time to trigger the spark plugs for ignition. 

If the TPS sensor sends a low input compared to the minimum voltage threshold (typically lower than 0.17 to 0.20 volts), your vehicle’s PCM logs the P0122 code and activates the check engine light. 

While DTC P0122 is a generic low voltage code, the exact repairs could vary per your car’s make, model, and PCM configuration. 

Moreover, several other OBD-II trouble codes relate to the performance of the throttle position sensor at position “A.” 

These include: 

• P0120: Throttle Position SensorSwitch A Circuit Malfunction 
• P0121: Throttle Position SensorSwitch A Circuit Range/Performance Problem 
• P0123: Throttle Position SensorSwitch A Circuit High Input 
• P0124: Throttle Pedal Position SensorSwitch (TPS) A Circuit Intermittent 

That’s why following the manufacturer’s pinpoint tests for each code is essential for correct diagnosis and repair.

Common symptoms

Like any other DTC code, the P0122 trouble code will activate the check engine light on your dashboard. 

In addition to the engine light turned on, you may also notice: 

• Engine stalling or surging
• Engine hesitating while accelerating
• Hard start 
• Rough, low, or very high idling 
• Minimal acceleration
• Increased emissions
• Your vehicle enters the failsafe mode 

Note: The failsafe mode is a safety feature offered by several car manufacturers to reduce the risks of your car’s system failures. 

In the failsafe mode (also known as “limp” mode), some of your vehicle’s features become limited, and your car’s speed is reduced to 40 mph or so. Your car’s ECM also doesn’t allow your transmission to shift as usual and only permits you to limp home or to a mechanic.

Can I still drive?

The severity of code P0122 can vary based on your vehicle’s make and model. 

Some cars may only warn you about the P0122 engine code by illuminating the check engine light. You may be able to drive your vehicle but shouldn’t do it for extended periods as you risk internal engine damage. 

On the other hand, some vehicles may immediately go into the failsafe mode. When that happens, you’ll find it pretty hard to accelerate, and your engine will possibly even stall.

So, if you have the engine light on due to the P0122 code, you should avoid driving your vehicle and get the code diagnosed and fixed ASAP.

P0122 causes

The voltage of the TP sensor can drop below the expected range for several reasons.

Sometimes things as simple as debris or a torn-up floor mat can block the accelerator pedal position sensor, triggering the P0122 code. 

Other possible reasons include:

• A loosely-mounted throttle position sensor
• A short circuit on the sensor (to the ground or another wire)
• A bad throttle position sensor
• A faulty TPS connector (harness connector)
• A faulty throttle position sensor switch
• Corroded sensor wiring
• The TPS sensor is mounted incorrectly
• Wrong throttle valve opening angle
• Issues with the powertrain control module

Diagnosis

The engine code P0122 can be triggered on any vehicle, regardless of whether it’s a Ford, BMW, or Honda Motor Company car. It could be due to anything from a bad throttle position sensor, a damaged PCM harness connector, to a shorted TPS circuit. 

Irrespective of the cause, this is an intermediate-level diagnosis and repair that requires specialized equipment and knowledge. That’s why it’s best to leave the task to the professionals. 

Here are the steps that your mechanic will follow: 

• Your mechanic will use an OBD-II scan tool to ensure no other engine code is present. Any additional engine code may help with a quicker diagnosis. 
• They’ll also check the freeze frame data to check the throttle position recorded by the sensor. Incorrect data could indicate a problem with the sensor or its wiring. 
• Your mechanic will visually inspect the wiring around the TPS sensor for any fraying or disconnection. They’ll also check the connector for any damage. 
• They’ll ensure that the throttle position sensor is mounted correctly. An incorrect position can result in low input or inaccurate TPS voltage levels. 
• If no issues are found in the above steps, the fault code is likely due to a bad throttle position sensor.

Possible repairs for P0122 & Costs

While P0122 is a generic powertrain fault code, the specific repair steps can vary depending on your vehicle’s make and model. 

To fix code P0122, your mechanic will need to locate the throttle position sensor on the throttle body. The exact location will likely be found in your car’s repair manual.

Once the root cause is diagnosed, here are the possible fixes: 

• Wiring or connector issue: If the sensor wiring is frayed or broken, it needs replacement. The wiring harness shouldn’t be rubbing against any other part or causing a short circuit to the ground. If the issue is with the sensor’s connector, it also needs a replacement. 
• Bad throttle position sensor: If the output voltage from the sensor is too low, it indicates a problem with the sensor and should be replaced. However, if the sensor has been replaced recently, it may need to be aligned or adjusted correctly.

When you take your car to an auto repair shop, most mechanics will first charge for an hour of diagnosis time. This can cost anywhere between $75-$150. 

Additionally, here’s the cost of replacing other parts (excluding labor charges):

• Sensor connector: $15-$40
• Throttle position sensor: $75 to $105