When you have a problem with your Nissan Sentra throttle position sensor (TPS), it can be hard to figure out where to start. Chances are if you have a stored OBDII DTC of P0120 for Throttle Position Sensor Signal Range/Performance, you will need to learn how to test a Nissan Sentra TPS. Today we’ll be showing you how to test a Nissan Sentra TPS in a 2002 Nissan Sentra with the 1.8 liter QG18DE engine in it.
Locating your TPS is just the beginning, because this model of Sentra TPS comes with two banks of connectors. These connectors work in conjunction to accurately read the angle of opening for your throttle blade. Based on this value, the ECU operates and runs your 1.8 liter QG16DE efficiently.
Your Nissan Sentra TPS is a three wire unit, and it’s the left mounted of the two three pin connectors. Remember to use the color code in our guide to help you recognize which wires you’ll be testing. With your Sentra throttle body closed, the signal from the TPS should be around 0.45 volts, and at fully open this voltage should be between 4.5 and 5 volts.
Your P0120 OBDII trouble code was turned on because your Sentra ECU has detected a signal from the TPS that does not fall within this range. Because of this, the P0120 trouble code is stored in your OBDII ECU, which translates to TPS A Circuit Malfunction.
The part number for this replacement throttle position sensor is Nissan part number 22620-4M501, or 22620-4M511. In order for you to learn how to test a Nissan Sentra TPS, you will need a multimeter to test the circuits at your QG18DE throttle. When using our guide, make sure you are checking the color codes for our wiring diagram to ensure you are testing your QG18DE TPS, and not the idle switch.
When your TPS has an issue, this can complicate matters causing a OBDII check engine light and making your Sentra run roughly. Some other symptoms of P0120 can include :
- Hard to start
- Poor idle
- Surging engine
- Check Engine Light is ON
How To Test a Nissan Sentra TPS for Power
Knowing how to test a Nissan Sentra TPS will involve testing the TPS for power and ground. To begin get your multimeter ready by putting it into volts DC mode, and put the black lead to the negative part of your battery.
Locate and unplug your TPS, and make sure to check our diagram above to make sure you are disconnecting the right plug. The pin you will be testing for voltage is PIN C, with the TPS unplugged, check the ENGINE side of the harness for switched power at this wire. If you don’t have power at this wire, double check to make sure you have your Sentra key in the ignition and turned to the “ON” position.
If you have voltage at this pin, the next part of our how to test a Nissan Sentra TPS DIY guide is checking for ground signal. The ground signal for this TPS is PIN A, and again you’ll be checking the ENGINE side of the harness for a low reference ground signal.
Now that you have both of those tests out of the way, the last leg of our how to test a Nissan Sentra TPS guide is to test the signal wire. Because the P0120 OBDII trouble code is specifically listing the signal voltage range as the culprit, this is the meat and potatoes part of our DIY article.
How To Test a Nissan Sentra TPS for Signal
For the last section of our tutorial on testing a Nissan Sentra TPS, you’ll be testing for signal. The signal pin on your TPS is PIN B, or the middle pin of your TPS. To test this part however, you will need to backpin your middle wire and reconnect your TPS.
To backpin this middle wire, take a paper clip and straighten it. Insert gently into the BACK of your wiring connector, making sure that the clip is making contact with the metal pin. Reconnect the entire TPS connector, and leave this paper clip sticking out from the back of the harness connector. You’ll be using this paper clip to test the voltage at the TPS, to make sure it’s within the range specified.
Insert your Nissan Sentra key into the ignition, and turn the key to the “ON” position. You can now test your signal wire on your Nissan Sentra TPS by measuring the voltage at the backpinned connector. To measure the voltage you will be grounding the black lead of your multimeter on the battery, and touching the red lead to the paper clip.
Now measure the voltage at the paper clip, which is the backpinned PIN B or middle pin on your TPS connector. With the key turned to “ON” and the engine off, the voltage with the 1.8 liter QG18DE throttle body closed should be between .2-.55 volts. Remember that this is with your Sentra throttle body completely closed.
You can now have a friend assist you by climbing into the car and depressing your gas pedal. This should open your QG18DE throttle all the way open, and the voltage at the middle wire with your throttle at Wide Open Throttle (WOT) should be roughly between 4.4-5.0 volts. If you find this value way out of specification, your QG18DE throttle body sensor may need calibration, or a completely new unit all together.
Replace your Nissan Sentra 1.8 liter throttle position sensor, and use a scan tool to remove the stored P0120 OBDII trouble code. Once you have the new throttle position sensor installed and calibrated, you can test drive your Sentra to see if your stored P0120 code is gone. You now know how to test a Nissan Sentra TPS, if you have any questions about our DIY guide, leave them for us below!
