How To Test The TPS With A Multimeter (1996-1998 3.0L V6 Nissan Quest)

As you're probably already aware, the throttle position sensor assembly on the 1996-1998 3.0L V6 Nissan Quest or Mercury Villager is made up of two components: a throttle position sensor and an idle switch.

In this tutorial, I'm going to explain how you can easily test the throttle position sensor portion of the assembly with a multimeter.

With your test results, you'll quickly find out whether the TPS is OK or toast, and whether the entire assembly needs to be replaced.

APPLIES TO: This tutorial applies to the following vehicles:

• 3.0L V6 Nissan Quest: 1996, 1997, 1998.
• 3.0L V6 Mercury Villager: 1996, 1997, 1998.

IDLE SWITCH TESTS:

• How To Test And Adjust The Idle Switch (1996-1998 3.0L V6 Nissan Quest).

TPS/IDLE SWITCH CIRCUIT DIAGRAM:

• TPS And Idle Switch Circuit Wiring Diagram (1996-1997 3.0L V6 Nissan Quest).
• TPS And Idle Switch Circuit Wiring Diagram (1998 3.0L V6 Nissan Quest).

Symptoms Of A Bad Throttle Position Sensor

The throttle position sensor assembly is bolted right onto the throttle body, and its job is to inform your Nissan Quest or Mercury Villager's throttle plate position to the powertrain control module (PCM).

To be a bit more specific, as you step ON or step OFF the accelerator pedal and the throttle plate opens or closes, the TPS sensor assembly measures the throttle plate angle and shoots this info to the PCM.

Since this throttle plate angle information is critical for keeping the engine running smoothly and for the transmission control module (TCM) to control the automatic transmission's shifts, when it fails, you're going to see one or more of the following engine performance issues.

• Hesitation when you tip into the throttle —You step on the gas and it seems like the engine "falls on its face" for a moment before power kicks in.
• Poor acceleration/weak power —You step on the gas pedal and the engine feels lazy, especially if you're pulling away from a stop or merging.
• Rough idle —The engine's idle isn't steady (may hunt up and down). You can feel the engine "shaky" especially at a stop light.
• Stalling (often at idle or when coming to a stop) —The engine may die when you let off the gas or when you shift into gear.
• Erratic throttle response —Throttle response feels inconsistent. In other words, stepping on the accelerator pedal doesn't always give you the same engine/power response.
• Weird/harsh/late automatic transmission shifting —Because the automatic transmission uses throttle angle/load info, a bad TPS signal can cause odd shift timing/feel.
• Check Engine Light (or stored fault code) —The PCM can flag the TPS circuit/signal as out of range.
  • P0120: Throttle Position Sensor Circuit.

Throttle Position Sensor Circuit Descriptions

There are two 3-wire connectors that connect to the throttle position sensor assembly on your Nissan Quest or Mercury Villager. One connector is brown, and the other is gray.

The brown connector connects to the throttle position sensor portion of the sensor assembly. The gray connector belongs to the idle switch portion of the sensor assembly.

Below, you'll find a brief description of the three circuits of the throttle position sensor portion of the sensor assembly, which we'll be using to test the TPS in the following test sections.

Terminal	Wire	Description
4	Brown (BRN)	5V Input
5	Red (RED)	TPS Signal Output
6	White with black stripe (WHT/BLK)	Sensor Ground Input

Where To Buy Your TPS/Idle Switch Sensor And Save

The throttle position sensor assembly isn't an expensive component. Still, it doesn't hurt to save some money.

In the following links, you'll find sensors from well-known automotive brands that I've used my entire automotive repair career and don't hesitate to recommend because they're reliable and don't cost an arm and a leg:

NOTE: Not sure if the above TP sensor fits your particular 3.0L Nissan Quest or Mercury Villager? Don't worry, once you get to the site, they'll make sure it fits by asking you the particulars of your vehicle. If it doesn't fit, they'll find you the right one.

TEST 1: Testing The TPS Voltage Signal

In a nutshell, this is how the throttle position sensor works when it's functioning correctly:

1. As the throttle plate opens, the TPS voltage signal increases from about 0.5 Volts to around 4.5 Volts at wide-open throttle (WOT) position.
2. As the throttle plate closes, the TPS voltage signal decreases smoothly back to baseline voltage.

You and I can easily check that the throttle position sensor is actually producing a variable voltage signal —as we manually open and close the throttle plate— by tapping into the white (WHT) wire of the brown 3-wire connector.

To test the TPS voltage signal output of the WHT wire, we're going to need to either back-probe the brown connector or use a wire-piercing probe on the wire itself, since the brown connector must remain connected to the throttle position sensor assembly during this TPS signal voltage output test.

My go-to method for doing this is using a wire-piercing probe. If you don't have one and need to buy one, this is the one I use and recommend: Goupchn 4mm Banana to Banana Plug Test Leads Kit (Amazon affiliate link).

Here are the steps:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Connect the red multimeter test lead to the RED wire of the sensor's brown 3-wire connector.
   
   The WHT wire connects to the terminal labeled with the number 2 in the illustration above.
   
   NOTE: Make your connections on the wire of the engine wiring harness connector, not on the wire coming out of the TPS sensor assembly itself. Also, all connectors must remain connected to each other during the test.

3. 3

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

4. 4

   Have your helper turn the key to the ON position, but don't start the engine (this will power up the TP sensor).

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 (by hand and from the engine compartment) while you observe the change in voltage numbers on your multimeter.
   
   As the throttle opens, the voltage numbers should increase.
   
   Once the throttle is wide open, your multimeter should read somewhere between 3.5 to 4.5 Volts DC.
   
   NOTE: For this test result to be accurate, you need to open the throttle by hand and not from inside the vehicle.

2. 7

   Slowly close the throttle.
   
   As the throttle plate closes, the voltage numbers should decrease to the exact same voltage you noticed in step 5.

Part 3

1. 8

   Lightly tap on the throttle position sensor with the handle of a screw-driver or something similar.
   
   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 glitch out (skip or go blank). If the TPS is OK, the tapping will have no effect on the voltage numbers.

2. 9

   Repeat step 8 several times to make sure of your multimeter test results.

Let's take a look at your test results:

CASE 1: The TPS signal voltage increased and decreased as you opened and closed the throttle plate. This test result lets you know the TPS portion of the sensor assembly is working like it should. In other words, it's not defective.

If you still suspect there's a problem with the throttle position sensor assembly, or you've got a TPS diagnostic trouble code (DTC) illuminating the check engine light that won't go away, there's a good chance the sensor assembly may be out of adjustment.

You can find the adjustment procedure in this tutorial: LINK GOES HERE.

CASE 2: The TPS signal voltage did not increase or decrease as you opened and closed the throttle plate. Having the TPS signal voltage output stay stuck, regardless of throttle plate position, usually tells you the throttle position sensor assembly is bad.

But before we replace it, we still need to make sure it's getting power and Ground from your Nissan Quest or Mercury Villager's PCM. For the first of these two tests, go to: TEST 2: Making Sure The TPS Is Getting 5 Volts.

CASE 3: The multimeter did not register any voltage at all as you opened and closed the throttle plate. When the multimeter reports no voltage at all during the TPS signal voltage output test, it usually means the sensor assembly isn't getting either power or Ground from the PCM —or the sensor itself could be bad.

We can continue troubleshooting by making sure the TPS is getting both 5 Volts and Ground from the PCM. For the first of these two tests, head over to: TEST 2: Making Sure The TPS Is Getting 5 Volts.

TEST 2: Making Sure The TPS Is Getting 5 Volts

The throttle position sensor gets power in the form of 5 Volts from the brown (BRN) wire of the brown 3-wire connector.

These 5 Volts, which are supplied by your Nissan Quest or Mercury Villager's PCM, are available only with the key in either the RUN or START position.

For our testing purposes, we're going to make sure these 5 Volts are present with the key in the RUN position and the engine OFF.

If the TPS sensor is getting power from your minivan's PCM, we'll move on to TEST 3 and make sure it's also getting Ground.

OK, let's begin.

1. 1

   Select Volts DC mode on your multimeter.

2. 2

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

3. 3

   Disconnect the brown 3-wire connector from the TPS/idle switch sensor assembly.

4. 4

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

5. 5

   With the red multimeter test lead probe the female terminal that connects to the BRN wire of the brown 3-wire connector.
   
   NOTE: Gently probe the female terminal with your multimeter test lead to avoid damaging it.

6. 6

   The multimeter should report 4.5 to 5 Volts DC.

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

CASE 1: The BRN wire is delivering 5 Volts DC. This test result confirms the PCM is supplying power to the TPS sensor.

Our next and final test is to make sure that the TPS sensor is getting Ground. Go to: TEST 3: Making Sure The TPS Is Getting Ground.

CASE 2: The BRN wire isn't delivering 5 Volts DC. Double-check that you're probing the correct terminal of the brown connector and that this terminal actually connects to the BRN wire and repeat the test.

If you still don't see 5 Volts present at the terminal, then we can rule out the TPS sensor itself as the cause of the TPS diagnostic trouble code (DTC) and the resulting engine performance issues, since without power the TPS can't produce a voltage signal the PCM can use.

Although it's beyond the scope of this tutorial to diagnose this issue further, your next step is to find out why those 5 Volts are missing from the circuit and fix the problem.

Once the TPS gets power, it'll function again and the TPS trouble code should clear, along with the engine performance issues.

The most likely cause of the missing 5 Volts in the BRN wire is an open-circuit problem between the brown TPS connector and the PCM connector.

TEST 3: Making Sure The TPS Is Getting Ground

If you've reached this point, your TPS sensor diagnostic tests have confirmed the following:

• TEST 1 —The TPS signal voltage is stuck or missing as you open and close the throttle plate.
• TEST 2 —The TPS is getting its PCM-supplied 5 Volts.

We're now going to make sure the TPS sensor is getting Ground on the white with black stripe (WHT/BLK) wire of the sensor assembly's 3-wire brown connector.

Just like the 5 Volts we tested in TEST 2, this Ground is supplied by the PCM, and we'll check it with the key in the RUN position and the engine OFF.

Let's get testing:

1. 1

   Select Volts DC mode on your multimeter.

2. 2

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

3. 3

   Disconnect the 3-wire brown connector from the TP sensor assembly.

4. 4

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

5. 5

   With the black multimeter test lead probe the terminal that connects to the BLK/WHT wire of the brown TPS 3-wire connector.
   
   NOTE: Gently probe the female terminal with your multimeter test lead to avoid damaging it.

6. 6

   The multimeter should report 10 to 12 Volts DC.

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

CASE 1: Your multimeter reported 10 to 12 Volts DC. This confirms that your Quest or Villager's PCM is supplying the Ground the TPS sensor needs to produce a variable signal as you open or close the throttle plate.

If you've confirmed the following conditions, then you can conclude the TPS sensor is toast and the assembly needs to be replaced:

• The TPS signal voltage stays stuck or is missing when you actuate the throttle plate (TEST 1).
• The BRN wire is delivering the 5 Volts from the PCM (TEST 2).
• In this last test section, you confirmed the TPS sensor is getting Ground from the PCM.

When it's time to replace the TPS sensor assembly, I want to recommend the following sensors. They're from known automotive brands I trust (Standard Motor Products and Hitachi), rely on, and don't hesitate to recommend:

• Standard Motor Products TH186 Throttle Position Sensor (Amazon affiliate link).
• Hitachi TPS0005 Throttle Position Sensor (Amazon affiliate link).

NOTE: The TPS sensor assembly must be adjusted to specification after replacement. You can find the step-by-step adjustment procedure here: How To Test And Adjust The Idle Switch (1996-1998 3.0L V6 Nissan Quest).

CASE 2: Your multimeter did not report the indicated voltage. Make sure the terminal you're probing actually connects to the WHT/BLK wire and repeat the test. If your multimeter still doesn't report the indicated 10 to 12 Volts DC, then this confirms the sensor isn't getting Ground from the PCM.

Although it's beyond the scope of this tutorial to figure out why this Ground is missing from the circuit, your next step is to troubleshoot the issue and restore this Ground to the WHT/BLK wire.

Once the TPS sensor receives Ground from the PCM, it'll function again, the TPS trouble code will clear, and the engine performance issues caused by this problem will clear as well.

The most likely cause of this missing Ground in the WHT/BLK wire is an open-circuit issue between the brown TPS connector and the PCM connector.

More 3.0L V6 Nissan Quest Diagnostic Tutorials

You can find a complete list of tutorials for your 3.0L V6 Nissan Quest and Mercury Villager here:

• 3.0L V6 Nissan Quest Index Of Articles.

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

• How To Test The Fuel Pump (1993-1998 3.0L V6 Nissan Quest).
• How To Troubleshoot A Cylinder Misfire (1993-1998 3.0L V6 Nissan Quest).
• How To Test The Fuel Injectors (1993-1995 3.0L V6 Nissan Quest).
• How To Test For A Blown Head Gasket (1993-1998 3.0L V6 Nissan Quest).