The 1996 and 1997 2.4L Nissan Altima with an automatic transmission uses a throttle position assembly that is two components in one. One part of the assembly is the throttle position sensor and the other part is the idle switch.
In this tutorial, I'll show you how to test the throttle position sensor part using only a multimeter.
Contents of this tutorial:
Symptoms Of A Bad Throttle Position Sensor
A bad throttle position sensor on your 1996-1997 2.4L Nissan Altima will set a trouble code and light up the check engine light (CEL). Here's a brief list of symptoms you'll see with the TPS fails:
- Check engine light (CEL) illuminated on your Altima's instrument panel.
- A TPS diagnostic trouble code (DTC) stored in the PCM's memory:
- P0120: Throttle Position Sensor Circuit.
- Your 2.4L Nissan Altima fails the 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.
TEST 1: Testing The Throttle Position Sensor Voltage Signal
To find out if the throttle position sensor is fried (or not) we're gonna' see if it's creating a throttle plate angle voltage signal with a multimeter (in Volts DC mode).
This is an ‘on car’ test, since we'll test the sensor while it's still connected to its connector and bolted to the throttle body. We'll manually open the throttle plate and see what voltage the TP sensor is outputting.
If the throttle position sensor (TPS) is fried, the voltage signal won't increase/decrease as you open/close the throttle plate.
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 lead probe the middle wire of the sensor's 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 1996-1997 Nissan Altima.
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: 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.