The fault code P0121 is a sign of a problem in your engine’s throttle (TP) position sensor. This code can cause serious problems and your vehicle may not start. The P0121 code is a ‘Throttle/Pedal position sensor “A” circuit range/performance problem’. The powertrain controller module (PCM/ECM), monitors the performance of the TP sensors. The PCM will set the P0121 code if it detects the sensor operating outside of a predefined range.
In some vehicles, a code can also be set if the signals from the manifold absolute (MAP) and TP sensors do not match.
The throttle position sensor measures the amount of throttle that is open. The throttle position sensor is only found on older vehicles that have mechanical throttle links, whereas newer vehicles equipped with electronic throttle control have two. The sensors are on the throttle body.
PCM uses data collected from TP sensors to calculate functions like idle speed, fuel distribution and automatic transmission shift points. In vehicles equipped with ETC the PCM or another control module uses the data from the sensors to control the throttle motor/throttle vale. Two TP sensors are used in this type of system to protect against possible failures.
P0121 is a serious fault code, particularly in vehicles equipped with ETC. The control module will put the vehicle in fault mode or safety mode. The vehicle’s acceleration and speed are limited. You may not be able to drive the vehicle in some cases.
This code can also be used to refer to the position of the accelerator pedal. It may indicate a fault with the TP sensor in some vehicles. In vehicles equipped with ETC, the control module will use a pair APP sensors to determine the position of the throttle motor.
The PCM sends a reference signal of 5 volts to the throttle position sensors. The typical measurement is idle = 0.5 voltage; full throttle = 4volts. The PCM will set fault code P0121 if it detects the throttle angle to be greater or lower than what it should be at a certain RPM.
Other fault codes related the TP sensor: P0120, P0122, P0123, P0124
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What are the possible causes of fault code P0121?
The fault code P0121 is caused by a number of factors. Below are some of the most common causes.
- Faulty throttle sensor
- Wiring or connection problems in the TP Sensor circuit
- Problems relating to the throttle body
- Problems with sensors other than MAP and MAF (e.g. Sensors MAP and MAF
- Problems with the Control Module (low probability)
- Faulty APP sensors
- APP Circuit Error
What are the symptoms of fault code P0121?
You may experience one or more symptoms when the P0121 is appear:
- Engine fault light illuminated
- Problems starting the engine
- Hesitation during acceleration
- Engine stalling
- Idle speed irregularity
- Black smoke during acceleration
- The vehicle can enter a fault mode or a safe mode. The vehicle will only be able to be driven at a very slow speed with a limited throttle.
How to Fix Fault Code P0121?
- It is important to check and correct loose or damaged cables.
- The data between the A and B circuits of the TP sensor should be compared and tested
- Replacement the TP Sensor
How serious is fault code P0121?
If you enter the fault mode of your vehicle due to the P0121 code, it may cause a variety of driving issues, such as stalling or limited speed.
