Today, if something unusual is happening to your car, you don’t need expert knowledge in car mechanics to get a glimpse of things. With the OBD-II scanner, every driver can scan their car at any moment if he notices anything suspicious. If all of a sudden you cannot start your car or you have problems when accelerating or decelerating, the issue could be a P0121 code.
What can you expect once you diagnose a P0121 code with an OBD-II scanner? A P0121 error code is a signal that the output voltage of the throttle position sensor “A” is out of recommended range. The problem is signaled by the engine control module (ECM) when it determines a value below 0.2 volts or above 5 volts.
The usual suspects for this error are problems with a dirty throttle body or an open or short circuit of the sensor circuit. This is a serious problem, and you should restrain from driving. In some cases, a bad throttle body will not allow a car to start. Stay with us if you want to learn how to properly manage and resolve this error code.
The Fundamentals of the P0121 OBD2 Code
A throttle is a part of the engine that controls airflow into the engine. Intake of air is essential in a work of an engine. The combustion process cannot be done without a proper amount of air, and there is where the throttle comes in. A throttle position sensor monitors the position of a throttle.
What Does the P0121 Code Mean?
The function of the throttle position sensor (TPS) is to monitor the air intake of an engine. Usually, it is located on the shaft of a butterfly valve. That way it can directly monitor the position of the throttle. If the sensor electronic circuit or body of the sensor is faulty, that will result in an issue with an intake. That results in a bad air-to-fuel mixture.
The ECM controls the work of the TPS by measuring the output voltage values. If it measures out of the normal operating voltage range, it will signal a P0121 in a case of a TPS “A” sensor.
Possible Causes of the P0121 Code
The most common causes associated with P0121 are:
- Faulty throttle body
- Dirty throttle body
- An open or short circuit on the (TPS)
- Problems with a connection on a connector
- Corrosion on the ends of connections.
How the P0121 Code Affects Your Vehicle
The P0121 code is one of those codes that you cannot ignore. The symptoms connected to it will impact the everyday ride and make it more uncomfortable.
Signs and Symptoms of a P0121 Code
The symptoms that almost always present together with P0121 are:
- The check engine light will turn on
- You will not be able to start the car
- Uneven work of the engine
- Black smoke coming out of the exhaust
- Lack of power and inconsistent acceleration
- Problems with vehicle stalling
- Knocking sounds coming from the engine
- Depending on the type of vehicle, it can go into failsafe mode
The Consequences of Ignoring a P0121 Code
Ignoring the P0121 will only raise the problems, and you will end up with additional repairs. If you are not hearing any knocking sounds from the engine, it means that you may still resolve this easily. If you are lucky, the car will go into limp mode, making driving almost impossible.
But, if you keep driving with the error code, that will eventually lead to increased cylinder temperatures. Those high temperatures will result in engine knocking. The result from it will lead to catastrophic engine damage.
Decoding the Diagnosis of the P0121 Code
The first step in diagnosing the P0121 code is with an OBD-II scanner.
How to Use an OBD-II Scanner for P0121 Code
- Connect the OBD-II scanner to the car’s computer
- Use the scan tool to search for the error codes
- Record any error that you found, and with the help of freeze frame data, determine when the message occurred
- If there are other messages, repeat the process for them too
- Clear all the errors and go for a test drive. Wait and see if and when the error will reappear
- Do a visual inspection of the TPS, it’s wiring, and connectors
- Measure the output voltage range for both sensors and compare them. Regular values are between 0.5 and 4.5 volts.
Interpreting Your OBD-II Scanner Results for P0121 Code
Sometimes the P0121 and P0122 diagnostic fault codes will come in pair. That means that you have a problem with both throttle position sensors. In case you get any additional code errors, diagnose them too, and fix them before the P0121 code.
Proven Fixes for the P0121 Code
The good thing about this code is that there are not many hidden causes for it. The problem is, in most cases, based on the throttle or its positioning sensor.
Step-by-step Troubleshooting Guide for P0121 Code
There are a couple of usual suspects for this code. You should check them first and resolve any issues that you find:
- The problem can be a faulty throttle position sensor. Test it, and if that is the case, the only thing you can do is replace it
- Bad wiring and connections are also common problems. Check the wiring and see if there are any melted or rusted wires
- Visually inspect the throttle body. If it is dirty, do a throttle body cleaning.
Check Out P0121 Throttle Position Sensor Troubleshooting Tips:
When to Seek Professional Help for P0121 Code
If you are not into DIY mechanic stuff, contact a professional. If you are stuck on electrical testing of the TPS, also leave the problem to a mechanic. If nothing from the list above solves the issue, pay a visit to a mechanic.
In some cases, resetting the TPS will help with the P0121 code. If not, that is a sure sign that the problem is serious.
How To Prevent the P0121 Code from Reoccurring
There is only a couple of things you can do, but those are proven to be effective:
- Clean the throttle body from time to time
- Visually check the wiring, and replace it if it is worn and damaged.
FAQs about the P0121 Code
Can I Still Drive with the P0121 Code?
Technically you can drive with a P0121 code. But, you will experience several problematic drive symptoms. Those include sluggish acceleration, reduction in engine power, and sometimes the car will go into safe mode.
Is the P0121 Code Serious?
Yes, a P0121 engine code error is serious. It is not recommended to drive a car with it. In case you diagnose the code, go to the nearest auto repair shop and ask for an estimate for repairs. This problem is not a suitable repair for DIYers because it needs to be fixed properly.
How Much Does it Cost to Fix a P0121 Code?
It depends on the problem:
– Throttle body cleaning costs between $220 and $290
– New throttle position sensor costs between $170 and $230
– Replacing a defective throttle body costs a bit more. Depending on the car model it will cost between $580 and $690
– Replacing the defective wiring can cost between $100 and $1000. The price is based on the type of wiring and the model.
Where Is the TPS Throttle Position Sensor Located?
The throttle position sensor is located on the throttle body, specifically on the butterfly shaft. That way it can directly monitor the position of the throttle.
How to Test a Throttle Position Sensor?
Before you attempt to test the TPS, you should clean the throttle body. Often unclean throttle body prevents the TPS to work properly. To clean the throttle get a rag or an old piece of cloth and dampen it with a carburetor cleaner. After you clean the throttle, check does it open and closes completely.
Now you can test the TPS. This operation is fairly simple. All you need is a multimeter:
– Set the multimeter on a 10 DC voltage range
– Place the black testing probe on the ground terminal of the TPS
– Place the red testing probe on the voltage terminal of the TPS
– The multimeter should show 5 volts.
If the value is above or below 5 volts, you should change the TPS.
You can determine if the TPS is working properly by testing its ground. To do this, follow these steps:
– Set the multimeter on a 20 DC voltage range
– Turn the ignition to the ON position without starting the car
– Place the red testing probe on a positive battery side, marked with +
– With the black testing probe, touch each TPS wiring tab. Once you find a wire with a 12-volt reading, you have found the ground. If none of the wires show that voltage, then the TPS isn’t grounded properly, and needs to be replaced.
A third way to do a throttle position sensor test is to check its signal voltage. With this test, you can fully diagnose if the sensor working properly or if it is defective. With this test you are checking does the TPS read the throttle plate properly in all cases – when it is open, half-open, or closed.
1. If the TPS is connected with a throttle you will need to get alligator clips
2. Touch each wire with a pin, and attach the multimeter probes to the pins with alligator clips
3. When the throttle plate is fully closed, the value should read between 0.2V and 1.5V, depending on the type of the sensor. If the multimeter shows 0, you need to continue with the other steps
4. Gradually start to open the throttle plate, and the reading should start to change. When it is fully open, the multimeter should show between 3.5V and 5V
The TPS is not working properly in these cases:
– The value reading on the multimeter suddenly jumps when opening the plate
– The readout doesn’t change for a prolonged time
– The voltage output doesn’t reach 5 volts when the plate is fully open
– When the output suddenly changes when you touch the sensor with a screwdriver.
Need More Help with a P0121 Code?
The P0121 code is usually not difficult to diagnose and resolve. There are only a handful of reasons for this code to appear, so fixing it should not be difficult. But, if the fixes from this article don’t resolve anything, contact a professional. Also, contact a mechanic if you don’t want to mess around with the multimeters and the OBD-II scanners. This is a serious issue, and address it properly.
