TPS TEST 3: Testing The TP Signal
OK, so far all of your tests have confirmed that the TP sensor is receiving juice (5 V) and ground, therefore it should be producing a good throttle position signal if all is good and this test will help you to find out.
You'll need someone to help you in this part to lightly tap on the throttle position sensor's body with a screw driver (or other appropriate tool) as you observe your multimeter and actuate the throttle.
OK, let's start testing:
- Part 1
- Put your multimeter in Volts DC mode.
- With the RED multimeter lead, and an appropriate tool, probe the circuit labeled with the number 2 in the photo.
- Connect the BLACK multimeter lead directly on the battery negative terminal.
- Turn the Key to its ON position but do not start the engine.
- Your multimeter should read about .9 to 1 Volt (the reading on your vehicle will vary just a little, about ± 1 volt).
- Part 2
- Now that everything is set up...
- Rotate the throttle plate by hand as you observe the multimeter.
- The multimeter's initial reading should increase smoothly as you open the throttle plate to its Wide Open Position.
- Now, slowly release the throttle plate to its fully closed position, all the while observing the multimeter's reading.
- The multimeter's voltage reading should decrease in a smooth and linear fashion.
- Part 3
- OK, now have your assistant tap on the throttle position sensor lightly with a hard object, such as the butt of a screw-driver's handle.
- Have your assistant tap on it as you progressively open the throttle to its open-wide position and as you slowly release it back to its closed position.
- All the while you've got your eyes glued on the multimeter to see if the tapping affects the voltage readings.
- Repeat this (tapping the TPS) several times to make sure of your results.
Interpreting The Results
If the throttle position sensor (TPS) is good, the DC voltage on the multimeter should increase smoothly until it reaches it maximum voltage, which is about 4.5 Volts DC. As you slowly release the throttle plate back to its closed position, the multimeter again should display a gradual decrease in voltage till it reaches the initial base voltage you recorded in the beginning of the test.
If the TPS is BAD, then there will be sudden gaps/loss of voltage as you increase or decrease the throttle plate's to its fully open or fully closed position, especially when you tap on the sensor. Or, there will be no voltage reading at all. OK then, here are the two possible outcomes:
CASE 1: If the multimeter registered a smooth increase or decrease in voltage, then the TP sensor is working OK and is not the cause of the TPS fault code issue. Go to: TEST 4: TPS Code Won't 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, then the throttle position sensor (TPS) is BAD. Replacing the throttle position sensor will solve the TPS diagnostic trouble code (DTC) lighting up your CHECK ENGINE LIGHT (CEL) on your Ford (or Lincoln or Mercury) car, Pick Up, or SUV.
TPS TEST 4: TPS Code Won't Go Away
So you've tested the TPS per the instructions in this article and according to the test results, the TPS is good... yet the CHECK ENGINE LIGHT is still on. Well, here are a couple of suggestions that might inspire your next diagnostic move:
- The throttle plate's idle-stop screw's factory adjustment has been altered so that the engine could be idled up and mask a miss/misfire and/or rough idle. This increases the TP sensor's signal to the PCM. The PCM doesn't like it and light ups the CHECK ENGINE LIGHT (CEL).
- The throttle cable is binding and causing the throttle plate to not fully close.
- This can be verified by simply having someone inside the vehicle pushing the accelerator cable to the floor and releasing it, with the engine OFF, while you visually check that the throttle plate and cable are not getting stuck somewhere in their travel.
- The TPS is failing intermittently. Which means that it works fine most of the time, but every now and then it doesn't:
- I have found that the best way to test these intermittents is to road-test the vehicle with the multimeter hooked up to the TP Signal Wire with a long wire so that I can comfortably observe the Signal going up and down as I or someone else drives.
- The TP sensor's connector is BAD, usually the locking tab is broken and the connector has worked itself loose, causing an intermittent false connection.
Where To Buy The Throttle Position Sensor And Save
The following links will help you comparison shop for the factory original Motorcraft and after-market throttle position sensor (TPS):
Not sure if the TP sensors above fit your particular Ford vehicle? Don't worry, once you get to the site, they'll make sure they fit and if they don't, they'll find you the right ones.
If this info really saved the day, buy me a beer!