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Virtually every car on the road today has a built-in central computer that monitors the performance of all the systems and components in the car.
When any of the systems fail, it sends wrong signals to the computer, which interprets the signals to adjust the performance of the engine, and in most cases, triggers the check engine light.
P0121 code is a Diagnostic Trouble Code (DTC) that indicates an issue with the Throttle Pedal Position Sensor/Switch (TPS) A range. This is not a severe issue, but it needs to be fixed as early as possible.
This article explains the symptoms, causes, and tips on how to clear the P0121 DTC from your vehicle.
What Does P0121 Code Mean?
Technically, the OBD definition of the P0121 code is Throttle Pedal Position Sensor/Switch (TPS) A Circuit Range Performance Problem.
The PCM/ECM stores this DTC when it detects the TPS “A” sensor is malfunctioning or not functioning at all.
Function of Throttle Pedal Position Sensor/Switch (TPS)
This sensor/switch is installed on the throttle body assembly of every vehicle; older cars may have just one of these sensors, but newer vehicles – with electronic throttle control (ETC) – have at least two.
The function of this sensor is to measure and monitor when the engine’s throttle blade opens up. As the throttle opens, this sensor’s (voltage) readings go up and send signals to the ECM/PCM. This operation is repeated several times as you drive.
Causes of P0121 Code
The Powertrain Control Module (PCM) or ECM provides a 5V reference signal to the TPS and ground too. The standard voltage measurement is .5V (during idling) and 4.5V in full throttle. So, if the ECM/PCM receives signals greater or less than the standard RPM range(s), it will store the P0121 DTC.
Listed below are other possible reasons why you got the P0121 code as you scanned your vehicle.
- The TPS intermittently opens internally
- The sensor harness is rubbing – causing an open or short in the wiring
- Bad wiring connection
- Faulty PCM (not common)
- Corroded connector or sensor
- The sensor circuit A sent an output range that’s above or below the specified voltage range when compared with the sensor circuit B.
Symptoms of P0121 Code
When the TPS fails, these are the most common issues you may face with your vehicle.
- Car refuses to start
- The Check Engine Icon/Light is on
- Throttle does not respond
- Engine stalling
- Thick black smoke comes out from the exhaust tailpipe when you accelerate
Is the P0121 Code Severe?
An issue with the throttle assembly is quite a serious one because it could cause your car not to start at all. Also, a failed TPS would make acceleration difficult – if not impossible. You should fix this code as soon as possible.
How to Fix the P0121 Code Issues
The following tips can help you to fix the P0121 code by yourself. However, if they are looking too technical, get a mechanic to do that for you.
1. Check the TPS Connector
If the TPS connector is bad, the sensor would always malfunction; so, you need to check this and have the connector replaced if it’s in bad shape.
2. Replace the Sensor
When you check and the connector is in good shape, check the sensor itself for physical damages or failure. Ensure to replace the sensor if you could detect any fault on the body.
3. Clean the Throttle Body Assembly
This is a technical action as it requires bringing down the throttle assembly to clean it thoroughly. Throttle body cleaning costs around $200 if done for you by an auto mechanic or technician.
4. Change the Throttle Body
If the throttle body housing all the throttle components, is cracked, you will need to buy a new one, which costs around $500 – $600.
Cost of Fixing P0121 Code
The amount you’d spend depends on what got spoilt. Below is a quick rundown of the cost of fixing this error code.
- Throttle Position Sensor $170-$230
- Body Cleaning $220-$290
- Throttle Body $580-$690
- Wiring repair/replacement $100-$1000
Price provided by the FIXD.com Team.
The P0121 code signifies a malfunctioning or failed Throttle Pedal Position Sensor/Switch (TPS). Fixing this issue would cause the TPS Switch “A” to output the expected voltage range and your car would run smoothly again.