Modern vehicles are marvels of engineering, with various intricate components working in harmony to ensure optimal performance. One such critical component is the throttle position sensor (TPS), which plays a pivotal role in regulating the engine’s air-fuel mixture. You probably have an issue you need to get fixed now, and don’t have time to read for an hour. I will give you the short answer up front.
Can the throttle position sensor cause an engine to run lean? The answer is yes, although, not as common as causing the engine to run rich. It is more common, when a TPS goes bad, you will start getting poor gas mileage, because it isn’t sending the correct info to the computer. A TPS commonly doesn’t tell the computer that the throttle is all the way closed when they go bad.
Understanding the Throttle Position Sensor
The throttle position sensor is a small yet indispensable device located on the throttle body of a fuel-injected engine. Its primary function is to monitor the position of the throttle valve, providing crucial information to the engine control unit (ECM). The ECM, in turn, utilizes this data to adjust the ignition and fuel injector timing. It also is responsible to letting the automatic transmission to know when to properly shift.
How Throttle Position Sensors Work
TPS typically consists of a potentiometer connected to the throttle shaft. As the driver presses the accelerator pedal, the throttle valve opens, and the sensor’s resistance changes accordingly. This change in resistance is then converted into voltage signals, which are sent to the ECM. The ECM interprets these signals to determine the precise position of the throttle, allowing it to make real-time adjustments to the fuel injection and ignition timing.
Symptoms of a Faulty Throttle Position Sensor
When a TPS malfunctions or fails, it can disrupt the delicate balance between air and fuel entering the engine, leading to a variety of issues. One of the potential problems associated with a faulty TPS is an engine running rich, resulting in poor fuel mileage. I highly recommend checking the codes with an ODB2 Diagnostic Scanner before assuming it is the throttle position sensor. You can find all the codes on my Diagnostic Code Page. Specific books may contain important information that isn’t generally published on an online search. Search The Mechanic Doctor for your best resources.
Before committing to your issue being a faulty Throttle Position Sensor, (TPS). Let’s look at the symptoms and bad TPS will give you.
- A decrease in fuel economy
- Sudden idle surges
- Bucking and jerking
- Engine stalling out
- Surges in speed while driving
- Check engine light and often random light on and off
- Transmission not shifting properly
- Poor acceleration or lack of power
- Rough idle
- Engine may appear to misfire
- Issue with the cruise control
Diagnosing TPS-Related Lean Conditions
Identifying whether a TPS is responsible for a lean-running engine involves a systematic approach. Mechanics often use diagnostic tools to measure the sensor’s voltage output and check for any irregularities.
Additionally, a visual inspection of the sensor’s wiring and connectors can reveal potential issues. Note, for proper testing, you will need to refer to automotive manuals or dealership to get the correct specifications. Voltages and resistance specifications will vary on different manufactures and years.
No matter testing the TPS on or off the car, you should have a wiring diagram to identify which terminals to test. If you do not have a diagram, there is a way to figure out what terminals to test.
Testing the TPS: Resistance Test
Testing a throttle position sensor (TPS) is a straightforward process, commonly performed using a digital multimeter. To begin, disconnect the TPS electrical connector and set the multimeter to measure resistance.
Connect the multimeter probes to the TPS terminals, and smoothly rotate the throttle to observe the changing resistance values. A healthy TPS should exhibit a gradual and linear decrease in resistance as the throttle opens. Any erratic readings or abrupt changes may indicate a faulty sensor. When the Throttle Position Sensor is wide open, it is an open circuit. Meaning there is no resistance.
Additionally, testing for voltage output using the multimeter can help ensure the TPS is transmitting accurate signals to the engine control unit, aiding in effective troubleshooting.
Testing the TPS: Voltage Test
Using a voltage/mulitimeter, you will want to identify the positive wire that runs to the TPS. Disconnect the connector going to the TPS. Set your volt meter to 12 volts DC, or in a range of 12 volts. Turn the ignition switch to the on position. Connect your black test lead to a good ground source on the engine or battery.
Touch the red lead to each pin on the connector until you find the specified voltage from the manufacturer. Commonly, this voltage will be 5 volts. Once you identify the pin with voltage, make note of it.
Set your multimeter to continuity test and test the remaining pins in the connector. You are looking for a straight connection between that pin and ground. Once you identify it, make note.
Plug the connector back up to the TPS. Using something like straight pins, stick them into the back of the connector for the two wires you identified. Do not let these pins touch each other as that can result in shorting out something.
Clip the red positive test lead to the wire with voltage. Clip the black test lead to the wire that is ground, you are ready to start testing.
Performing the Throttle Position Sensor Test
For this example, we will base that this TPS runs with 5 volts. With the throttle closed in idle position, the voltage should be reading low. Let’s say 1 volt. As you slowly turn the throttle to wide open, the voltage should smoothly increase. Once the throttle is wide open, (WOT), the voltage should be 5 volts.
If the voltage is still lower than 5 volts in the (WOT) position, the engine will run lean. Voltage jumping to 5 volts before you get to the (WOT) position, then it will run rich. Erratic voltage jumping around or doesn’t increase smoothly, it also means the TPS is bad. Another tool you can use to test a throttle position sensor is a diagnostic scanner. One of the best to use without breaking your wallet is the Autel AL539.
Conclusion
In conclusion, the throttle position sensor is a crucial component in ensuring the proper functioning of a vehicle’s engine. While a faulty TPS can indeed contribute to an engine running lean. It’s important to note that other factors more than likely also play a role.
The function of a TPS does contribute to controlling the fuel mixture. Its job is to tell the computer, (ECM) what position the throttle is in. The ECM needs this information to adjust the ignition and fuel timing. It also needs this information for the transmission.
If you are getting codes indicating a lean burn, look at the MAF sensor first. The MAF sensor actually does affect the fuel mixture. Measure your fuel pressure before and after the fuel pressure regulator if you can. Low fuel pressure and a faulty fuel pressure regulator can cause a lean mix as well.
If everything else checks out, then look to the TPS. If the TPS is reading like 75% open, when it really is all the way wide open. Then this can cause the engine to run lean. You can also get the reverse issue, and the TPS cause the engine to run rich. I can tell you from personal experience of 45 years working on cars. Usually when the TPS goes bad, you get a rich mixture and start having poor gas mileage.
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