How To Test The TPS (1997-1999 1.6L Nissan Sentra)

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 an automotive scan tool. Moreover, you don't need to remove the TPS assembly from the throttle body to test it.

ES You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1997-1999 1.6L Nissan Sentra) (at: autotecnico-online.com).

NOTE: This tutorial applies to the following vehicles:

• 1.6L Nissan Sentra: 1997, 1998, 1999.
• 1.6L Nissan 200 SX: 1997, 1998.

IDLE SWITCH TEST: 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).

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)
Terminal	Wire	Description
1	PNK/BLU	5 Volt
2	YEL	Throttle Position Signal
3	BLK	Ground

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:

1. 1

   Turn the key to the ON position but don't crank or start the engine.

2. 2

   Place your multimeter in Volts DC mode.

3. 3

   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.

4. 4

   Ground the black multimeter test lead on the battery negative (-) terminal.

5. 5

   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.

Part 2

1. 6

   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.

2. 7

   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.

3. 8

   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.

Part 3

1. 9

   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.

2. 10

   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, go to: TEST 2: Verifying The TPS Is Getting 5 Volts.

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 The TPS Is Getting 5 Volts.

TEST 2: Verifying The TPS Is Getting 5 Volts

Like any other electrical component under the hood, the TPS sensor needs power and Ground to function. So before concluding that the TP sensor is toast, we need to make sure it's getting both.

In this test section, we're going to verify that it's receiving 4.5 to 5 Volts from the PCM. The wire that delivers these 5 Volts (from the PCM to the TPS sensor) is the pink with blue stripe (PNK/BLU) wire on the TP sensor's 3-wire connector.

NOTE: This test is done on the connector that plugs into the throttle position sensor portion of the TPS assembly. In other words, we're going to check for power directly at the female terminal of the 3-wire connector that corresponds to the PNK/BLU wire.

Let's get started:

1. 1

   Disconnect the TPS sensor from its 3-wire connector.

2. 2

   Place your multimeter in Volts DC mode.

3. 3

   Connect the black multimeter test lead to the battery negative (-) post.

4. 4

   Turn the key to the ON position but don't crank or start the engine.

5. 5

   Probe the female terminal (of the connector) that connects to the PNK/BLU wire with the red multimeter test lead.

6. 6

   Your multimeter should read 4.5 to 5 Volts DC.

Let's take a look at what your test results mean:

CASE 1: The multimeter confirms the TPS is getting 4.5 to 5 Volts DC. This is the correct and expected test result and it confirms the PCM is supplying power to the TPS sensor.

Your next step is to make sure that the TP sensor portion of the TPS sensor assembly is getting Ground. For this test, head over to: TEST 3: Verifying The TPS Is Getting Ground.

CASE 2: 4.5 to 5 Volts are not present. Double-check that you're testing the correct terminal on the TP sensor pigtail connector and repeat the test.

If your multimeter still doesn't show 4.5 to 5 Volts DC, then we can conclude the TP sensor itself is OK, since without power it's not going to function.

The most likely cause of this missing voltage is an open-circuit in the 5-Volt supply wire between the TP sensor connector and the PCM connector. Although troubleshooting these missing 5 Volts is beyond the scope of this tutorial, your next step is to find out why they're missing and restore them to the circuit.

Once the TP sensor is getting power again, it will function normally and the TPS diagnostic trouble code will go away.

TEST 3: Verifying The TPS Is Getting Ground

So far, your TP sensor diagnostic has confirmed the following:

• TEST 1: The TP voltage signal is either stuck or missing as you open and close the throttle plate.
• TEST 2: The PNK/BLU wire is delivering power from the PCM to the sensor.

In this last test section, we're going to make sure the PCM is supplying the sensor with Ground. This Ground is delivered to the TP sensor through the black (BLK) wire of the sensor's 3-wire connector. We'll use a simple multimeter test to verify its presence.

This PCM-supplied Ground is only available with the key in the ON or START position. For our testing purposes, we'll check for this Ground with the key ON and the engine OFF.

IMPORTANT: Since this is a PCM-supplied Ground, do not connect this wire to battery voltage, or you risk damaging the PCM. The multimeter voltage test outlined in the instructions below is a safe way to confirm the presence of Ground in this circuit.

NOTE: This test is done on the connector that plugs into the throttle position sensor portion of the TPS assembly. In other words, we're going to check for Ground directly at the female terminal of the 3-wire connector that corresponds to the BLK wire.

These are the test steps:

1. 1

   Disconnect the TPS sensor from its 3-wire connector.

2. 2

   Place your multimeter in Volts DC mode.

3. 3

   Connect the red multimeter test lead to the battery positive (+) post.

4. 4

   Turn the key to the ON position but don't crank or start the engine.

5. 5

   Probe the female terminal (of the connector) that connects to the BLK wire with the black multimeter test lead.

6. 6

   Your multimeter should read 10 to 12 Volts DC if the PCM is supplying Ground.

Let's take a look at what your test results mean:

CASE 1: The multimeter confirms the TPS is getting Ground. This is the correct and expected test result and it confirms the PCM is supplying Ground to the TPS sensor.

You can conclude that the TPS is bad only if all tests have confirmed that:

1. The TP sensor is not providing a varying voltage signal when manually opening/closing the throttle plate (TEST 1).
2. The TP sensor is being fed 5 Volts DC (TEST 2).
3. The TP sensor is being fed Ground (this test section).

Therefore, you can conclude that the throttle position sensor is bad and needs to be replaced (and that this will solve the TP sensor code lighting up the check engine light).

CASE 2: Ground is not present. Double-check that you're testing the correct terminal on the TP sensor pigtail connector and repeat the test.

If your multimeter still doesn't show 10 to 12 Volts DC, then we can conclude the TP sensor itself is OK, since without Ground it's not going to function.

The most likely cause of this missing PCM-supplied Ground is an open-circuit in the Ground wire between the TP sensor connector and the PCM connector. Although troubleshooting this missing Ground is beyond the scope of this tutorial, your next step is to find out why it's missing and restore it to the circuit.

Once the TP sensor is getting Ground from the PCM again, it will function normally and the TPS diagnostic trouble code will go away.

More 1.6L Nissan Tutorials

You can find a complete list of tutorials in this index: Nissan 1.6L Index Of Articles.

Here's a small sample of the 1.6L Nissan tutorials you'll find in the index:

• How To Test Engine Compression (1.6L Nissan).
• How To Test For A Blown Head Gasket (1.6L Nissan).
• How To Test The Idle Switch (1997-1999 1.6L Nissan Sentra).
• Mass Air Flow (MAF) Sensor Test Nissan Sentra 1.6L (1995-1999) (at: easyautodiagnostics.com).