Testing the throttle position sensor on your 1990-1994 Nissan 3.0L Pathfinder (3.0L D21 Pickup) is not hard and can be done with a multimeter.
As you're already aware, the TPS is two components in one assembly. One part of the assembly is an idle switch and the other is the throttle position sensor (this is the reason why the TPS assembly has two connectors).
In this tutorial, I'll show you how to test the throttle position sensor part of the TPS assembly with 3 simple tests. Depending on the results of these 3 tests, you'll be able to accurately diagnose the throttle position sensor as bad (or not).
Contents of this tutorial at a glance:
- Symptoms Of A Bad Throttle Position Sensor.
- TEST 1: Testing The Throttle Position Sensor Voltage Signal.
- TEST 2: Verifying The Throttle Position Sensor Has Power.
- TEST 3: Verifying The Throttle Position Sensor Has Ground.
- Where To Buy Your Throttle Position Sensor And Save.
- More 3.0L Nissan Tutorials.
NOTE: To see if this tutorial applies to your specific 3.0L equipped Nissan, take a look at the Applies To: box on the right column.
You can find this tutorial in Spanish here: Cómo Probar El Sensor TPS (1990-1994 3.0L Pathfinder) (at: autotecnico-online.com).
Symptoms Of A Bad Throttle Position Sensor
In a nutshell, the fuel injection computer on your 3.0L Pathfinder (3.0L D21) needs the throttle position sensor to let it know how much the throttle plate opens or closes as you step on (or off) the accelerator pedal (since the accelerator pedal is connected to the throttle plate via a cable).
With the throttle position info the fuel injection computer can now: inject more/less fuel, advance/retard ignition timing, etc.
Being that the TPS is a critical input sensor of the engine management system, when it fails your 3.0L Nissan is gonna' resent it. You'll see one or more of the following symptoms:
- A TPS diagnostic trouble code (DTC) stored in the PCM's memory:
- 43 Throttle Position Sensor.
- Your Pathfinder fails the smog check (state mandated emissions test).
- Bad gas mileage.
- Hard start and/or extended cranking time (after shut off).
- Black smoke coming out of the tailpipe.
- Hesitation when accelerating your vehicle down the road.
Thankfully, the TPS can be tested without a scan tool and in the next section we'll start with the very first test.
TEST 1: Testing The Throttle Position Sensor Voltage Signal
The voltage signal that the TPS produces, when the throttle plate is closed, is around 0.4 Volts DC. As the throttle plate opens, this voltage increases. At the wide open throttle (WOT) position the TPS produces about 4 Volts DC.
Knowing this lets us test the sensor's performance with a multimeter and that's what we'll do to find out if it's good or bad.
NOTE: The throttle position sensor has to remain connected to its connector for this test to work (this is where a wire piercing probe comes in handy to get to the signal inside the wire. To see what one looks like, click here: Wire Piercing Probe Tool).
OK, let's start:
Place your multimeter in Volts DC mode and with the red multimeter test lead probe the middle wire of the TPS sensor's connector.
Ground the black multimeter test lead on the battery negative (-) terminal. Have your helper turn the key ON, but don't start the engine (this will power up the TP sensor).
Your multimeter should report a voltage around 0.4 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 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 confirms that the TP sensor is doing its job and is not defective.
CASE 2: The throttle angle voltage DID NOT increase (and/or decrease) as you opened and closed the throttle plate. This tells you that the TPS, on your 3.0L Nissan Pathfinder is bad.
Before you run out and buy it, I'm gonna' suggest that you do two more tests. One is to check that the TPS is getting power. The other is to check that it's Ground. To check that the TPS is getting power, 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.