The throttle position sensor is another computer sensor that is often misdiagnosed. Popular replacement TPS sensors are available at the bottom of this page but please test your old one before replacing it.
What should you do if you find a TPS sensor code set in the computer's memory? Both professional and DIY auto mechanics will often replace the component just because the code has set.
As I have learned in the school of hard knocks, just because a sensor has set a code does not mean that the part has failed. The sensor may be trying to tell you the truth and other related wiring problems could actually be causing the malfunction. When I see a voltage high or low code I often find a damaged connector or wires between the throttle body and PCM.
The TPS sensor is a potentiometer type of electrical component. Rather than just being opened or closed like a switch, the TPS controls the circuit by varying its resistance in response to throttle position.
In most cases this sensor will send a very low voltage back to the vehicle's main computer when the throttle plates are fully closed. This reference voltage increases as the throttle plates are opened.
Some manufacturers use inverse voltage readings for feedback. A bad part can cause many problems in the vehicle's overall performance. Inaccurate data can cause transmission problems as well.
Some of the conditions related to TPS sensor problems can be no up shifting, fast up shifts, late or delayed shifts, and line pressure problems that control internal solenoids and torque converter clutch engagement. Engine related problems can include "tip in" or hesitation when cracking the throttle plates.
You can test a throttle position sensor with an automotive scan tool. This is probably the easiest and most cost-effective way to diagnose a TPS problem.
Although the scan tool will have to be capable of displaying the data stream. Some of the cheaper scan tools only read and erase check engine light codes.
The TPS value can be analyzed on the scan tool and the throttle slowly depressed looking for either increase or decrease in voltage. Any dead spots or opens in the potentiometers will show up as a momentary flash of 0 V on the scanners data stream.
You can also test this computer sensor with an inexpensive automotive meter. You will most likely need an electrical diagram to identify the five Volt reference and output voltage wires that go to the vehicle's main computer.
Back probing the lead will provide a voltage value. The readings should change as you open the throttle Slowly. Again a dead spot in the throttle position sensor will show up as zero voltage as the dead spot is engaged. Professional mechanics prefer testing this component with a scope.
The waveform can be displayed on the scope display in real time and the DC signal monitored as the throttle is opened and closed. The voltage output of a Tps sensor will typically range from .5 V to 4.5 V at wide-open throttle. Note that I added the The Innova 3100 OBD2 Diagnostic Tool below that has a lot of capabilities for under 100 bucks. This can also pick up and track spikes in the signal voltage through a snapshot mode.
Change in voltage should be smooth with no dead spots or spikes. Looking for a glitch in the signal is easiest with a data recording Lab scope. But can be performed with both the scan tool and a digital voltmeter as described above.
In most cases a replacement TPS sensors is considered an electrical component and is not returnable. If your vehicle has set a code for a throttle position sensor takes the time to perform some tests before replacing the nonrefundable electrical car part.
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