As you're probably already aware, the TP sensor on the 2000-2001 1.8L Nissan Sentra has two connectors. This is because the TP sensor houses two sensors within the same assembly.
Part of the TPS assembly is an idle switch. The other part is the throttle position sensor.
In this tutorial I will show you how to test the throttle position sensor part with a multimeter (you don't need a scan tool). Moreover, you don't need to remove the TPS assembly from the throttle body to test it.
The contents of this tutorial at a glance:
- Symptoms Of A Bad Throttle Position Sensor.
- TEST 1: Testing The TPS Voltage Signal.
- TEST 2: Verifying Throttle Position Sensor Has 5 Volts And Ground.
- More 1.8L Nissan Tutorials.
Puedes encontrar este tutorial en Español aquí: Cómo Probar el Sensor TPS (2000-2002 Nissan 1.8L Sentra) (en: autotecnico-online.com).
Symptoms Of A Bad Throttle Position Sensor
TPS sensor's function is to inform your Nissan's fuel injection computer how much the throttle plate opens or closes as you depress or release the accelerator pedal.
With this throttle plate angle information (and that of other fuel and ignition system input sensors), the fuel injection computer can inject more or less fuel.
Since the TPS is a critical sensor for the engine management, when it fails you'll see one or more of the following trouble codes:
- P0122: Throttle Position Sensor Circuit Low Input.
- P0123: Throttle Position Sensor Circuit High Input.
- P1121: Throttle Position Sensor Signal Lower Than Expected.
- P1122: Throttle Position Sensor Signal Higher Than Expected.
To diagnose the TP sensor we need to know which wires, of the engine wiring harness TPS brown connector, feed it voltage and ground. We also need to know which wire is the one that carries the TPS signal to the fuel injection computer.
Here goes a brief description of the 3 TPS circuits (wires):
|TPS Circuits (2000, 2001, 2002 1.8L Nissan Sentra)|
|2||YEL||Throttle Position Signal|
TEST 1: Testing The TPS Voltage Signal
To successfully diagnose the TP sensor, on your 1.8L Nissan Sentra, you need to know:
- The TPS sensor produces a signal in Volts DC, and that this voltage increases when the throttle plate opens.
- The voltage value (at wide open throttle) returns to its closed throttle value once throttle plate closes (returns to its rest position).
The cool thing is that, with the help of a multimeter, you can check the voltage increases and decreases when opening and closing the throttle plate.
If the TP sensor is defective... TPS voltage signal will stay fixed at a single value (in other words, the voltage value will not increase/decrease when opening/closing the throttle).
NOTE: The TPS, on your Nissan Sentra, has a brown and a gray connector. The brown connector belongs to the TPS. The gray connector belongs to the idle switch part of the TPS assembly.
IMPORTANT: This test is done with the TP sensor mounted in its place on the throttle body and connected to its connector. You don't need to remove it to bench test it. Also, you'll need to use a wire-piercing probe or a back-probe to measure the TP signal voltage. To see what a wire-piercing probe looks like, go here: Wire Piercing Probe.
Here are the steps :
Place your multimeter in Volts DC mode and with the RED multimeter lead probe the middle wire of the sensor's brown connector. This is the wire that connects to pin #2 in the illustration above.
Ground the BLACK multimeter test lead on the battery negative terminal. Have you helper turn the Key On, but don't start the engine (this will power up the TP sensor).
Your multimeter should report a voltage between .2 to .9 Volts DC. If your multimeter doesn't, don't worry about it just yet, continue with the other steps.
Now, slowly open the throttle (by hand and from the engine compartment) while you observe the change in voltage numbers on your multimeter.
For this test result to be accurate, you need to open the throttle by hand and not from inside the vehicle.
As the throttle opens, the voltage numbers will increase. This increase in voltage should be smooth and without any gaps or skips. Once the throttle is wide open, your multimeter should read somewhere between 3.5 to 4.5 Volts DC.
Now, slowly close the throttle. As the throttle is closing, you should see the voltage decrease smoothly and without any gaps or skips, to the exact same voltage you noticed in step 4.
OK, now you'll need someone to help you lightly tap on the throttle position sensor with the handle of a screw-driver (or something similar, and I want to emphasize the words ‘lightly tap’) as you slowly open and close the throttle and observe the multimeter.
If the TPS is bad, the tapping will cause the voltage numbers to skip or go blank. If the TPS is OK, the tapping will have no effect on the voltage numbers.
Repeat step 7 several times to make sure of your multimeter test results.
Let's take a look at your test results:
CASE 1: The throttle angle voltage increased and decreased as you opened and closed the throttle plate. This test result confirms that the TP sensor is OK and not defective.
CASE 2: The throttle angle voltage DID NOT increase (and/or decrease) as you opened and closed the throttle plate. This test result confirms the throttle position sensor trouble code lighting up the check engine light on your 2000-2002 1.8L Nissan Sentra.
If I where in your shoes and to be sure that the TPS has truly failed, I would still make sure that the TP sensor is getting both power and ground. To check for power on the LT GRN wire, go to: TEST 2: Verifying Throttle Position Sensor Has 5 Volts And Ground.
CASE 3: Multimeter DID NOT register any voltage, this test result doesn't condemn the TP sensor as BAD just yet. Why? Because...
... the TP sensor may be missing either power or ground. So the next step is to check that the TP sensor is getting power, go to TEST 2: Verifying Throttle Position Sensor Has 5 Volts And Ground.