The 1996-2003 3.8L Ford Windstar throttle position sensor is a three wire sensor that can be easily and accurately tested with a multimeter.
With the help of this tutorial, you'll be able diagnose a malfunctioning throttle position sensor and or troubleshoot diagnostic trouble codes (DTCs) P0121, P0122, P0123 on your Ford 3.8L V6 equipped Windstar mini-van.
The throttle position sensor diagnostic test is divided into three parts. All of them are explained in a step-by-step way.
Contents of this tutorial:
I've written several other Ford 3.8L specific ‘How to Test’ articles the you can find at: Ford 3.0L and 3.8L Index of Articles.
TPS TEST 1: Testing The TPS Signal
The first order of business, to find out if the throttle position sensor (TPS) is bad or not, is to see if it's producing a throttle position signal. Before you start, I recommend you read the entire article first, especially read the section: How The Throttle Position Sensor Works.
You'll need someone to help you test the throttle position sensor. OK, let's start:
Start and warm up the engine on your 3.8L Ford Windstar mini-van. It's important that the throttle position sensor be at normal engine operating temperature.
Select Volts DC Mode on your multimeter and with the RED multimeter Lead probe the Gray with White stripe wire of the throttle position sensor. This is the wire that connects to the TPS terminal labeled with the number 2 in the illustration above.
The throttle position sensor, on your 3.8L Ford mini-van's engine, has to remain connected to its electrical connector while doing this test.
Ground the black multimeter test lead on the battery negative terminal and then have your helper turn the Key On but don't start the engine.
You should see you multimeter register 0.5 to 0.9 Volts DC. If it doesn't, don't worry about it just yet, continue with the other steps.
Now, slowly rotate the throttle manually while you observe your multimeter.
For this test result to be accurate, you need to rotate the throttle by hand and not from inside the mini-van.
As the throttle opens, the voltage reading should increase smoothly and without any gaps or skips. Once the throttle is wide open, your multimeter should read about 4.5 to 4.9 Volts DC.
Now, slowly return the throttle to its closed position. As this is happening, the voltage readings, on your multimeter, should 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.
The purpose of the tapping is to see if this will cause gaps or skips in the voltage readings. If the TPS is good, no amount of tapping will cause the multimeter voltage readings to skip or go dead.
Repeat step 8 several times to make sure of your multimeter test results.
Interpreting The Results
CASE 1: If the multimeter registered a smooth increase or decrease in voltage with no gaps, then the throttle position sensor, on your 3.8L Ford mini-van, is good and you don't need to do TPS TEST 2 or 3.
Now, if the throttle position sensor code won't go away, take a look at the info found at: TPS Code Will Not Go Away for a few more suggestions as to what could be causing the TPS diagnostic trouble code (DTC).
CASE 2: If the multimeter DID NOT register a smooth increase or decrease in Voltage, and you saw the voltage reading skip or go dead when tapping the TPS, then this means that the throttle position sensor (TPS) is bad. Replace the throttle position sensor.
CASE 3: If the multimeter DID NOT register any voltage, this is not good, but doesn't condemn the TPS as bad yet.
The TPS may be missing either power or Ground and you can test these also, go to TPS TEST 2.