The throttle position sensor (usually referred to as just the TPS) on the Nissan Sentra 1.6L with an automatic transmission is a set of two sensors within the same assembly.
One part of the TPS assembly is an idle switch. The other part is the actual throttle position sensor.
In this tutorial I'll show you how to test the TPS part of the assembly with a multimeter and without a automotive scan tool. Moreover, you don't need to remove the TPS assembly from the throttle body to test it.
Contents of this tutorial:
NOTE: If you need to test the idle switch part of the throttle position sensor assembly, this tutorial will help: How To Test The Idle Switch (1997-1999 1.6L Nissan Sentra).
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1997-1999 1.6L Nissan Sentra) (at: autotecnico-online.com).
Symptoms Of A Bad Throttle Position Sensor
The TP sensor's job is to measure the throttle plate angle, which opens and closes as a direct result of stepping on or off the accelerator pedal (a cable connects the accelerator pedal to the throttle plate on the throttle body).
Since the 1997-1999 Nissan Sentra 1.6L comes equipped with the OBD II diagnostic system, when the throttle position sensor fails, you'll see one 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.
Your Nissan Sentra's fuel injection computer receives the throttle plate position information through the middle wire of the TP sensor's brown connector (the gray connector is for the idle switch part of the TPS assembly). The other two wires feed voltage and Ground the TPS sensor.
In the table below you'll find a brief description of these three wires (circuits):
|TPS Circuits (1997, 1998, 1999 1.6L Nissan Sentra)|
|2||YEL||Throttle Position Signal|
Where To Buy The TPS And Save
If the TPS is bad and you want to save some bucks on its purchase, check out the following links. I think they'll save you a few bucks:
Not sure if the above TPS fits your particular 1.6L Nissan? Don't worry, once you get to the site they'll make sure it fits by asking you the specifics of your particular Nissan vehicle. If it doesn't fit, they'll find you the right one.
TEST 1: Testing The TPS Voltage Signal
The TP sensor produces a signal in Volts DC. This voltage signal increases as the throttle plate opens and returns to its original value as the throttle plate returns to its closed position.
The cool thing is that, with the help of a multimeter, we can check if the voltage increases/decreases as we manually open/close the throttle plate.
If the TP sensor is faulty, then the TP voltage signal will stay fixed at a single value (in other words it won't increase/decrease as the throttle plate opens/closes).
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.
Here are the steps :
Turn the key to the ON position but don't crank or start the engine.
Place your multimeter in Volts DC mode.
Connect the red multimeter test lead to 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.
Your multimeter should report a voltage between 0.2 to 0.9 Volts DC. If your multimeter doesn't, don't worry about it just yet, continue with the other steps.
Slowly open the throttle plate (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 plate by hand and not from inside the vehicle.
As the throttle plate opens, the voltage numbers will increase.
This increase in voltage should be smooth and without any gaps or skips. Once the throttle plate is wide open, your multimeter should read somewhere between 3.5 to 4.5 Volts DC.
Slowly close the throttle plate.
As the throttle plate 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.
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 plate 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 9 several times to make sure of your multimeter test results.
Let's take a look at your test results:
CASE 1: The throttle plate 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 plate 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 1997-1997 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 Power.
CASE 3: The 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 Power.