FORD TPS SENSOR REPLACEMENT PART 2
TPS TEST 1: Testing the 5 Volt Reference Signal
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The very first test we'll do, is to make sure that the throttle position sensor (TPS) is getting power.
As you already know, this power is in the form of 5 Volts DC and is provided by the PCM.
This test (as all of the tests in this article) must be done with a multimeter, either digital or analog. Also, I recommend that the engine be at its operating temperature... since the heat accumulated by the TPS from the engine may help to find a stubborn glitch in the sensor.
These are the steps:
- Remove any plastic covers that may be hiding the TPS from view and access.
- Put your multimeter in Volts DC mode (don't have a digital multimeter? Need to buy one? Click here to see my recommendations: Buying a Digital Multimeter for Automotive Diagnostic Testing).
- With the RED multimeter lead, and an appropriate tool, probe the circuit labeled with the number 1 in the photo.
- Connect the BLACK multimeter lead to a good and clean ground point on the engine or directly on the negative battery terminal.
- Turn the Key to its ON position but do not start the engine.
- Your multimeter should read 4.5 to 5 Volts.
CASE 1: If the multimeter registered 4.5 to 5 Volts, then the PCM is feeding the appropriate voltage. The next step is to test the Signal Return Circuit, TEST 2: Testing the Sensor Return (Ground) Circuit.
CASE 2: If the multimeter DID NOT register 4.5 to 5 Volts, then the PCM is NOT feeding the appropriate voltage either because there's an open short in the circuit or the PCM is fried. Altho' testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your Ford vehicle as being the cause of the problem and/or the TPS diagnostic trouble code (DTC) lighting up the check engine light (CEL).
TPS TEST 2: Testing the Sensor Return (Ground) Circuit
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If you've reached this point, then you've confirmed that the TPS is getting power (5 Volts DC) from the PCM.
The next test is to confirm that the PCM is feeding the TPS with ground.
This test follows pretty much the same procedure as TEST 1. Just a friendly reminder... the Ground Circuit is provided by the PCM, so do not short this circuit to Power (12 Volts) either intentionally or accidentally.
OK, let's start:
- Put your multimeter in Volts DC mode.
- With the BLACK multimeter lead, and an appropriate tool, probe the circuit labeled with the number 3 in the photo.
- Connect the RED multimeter lead directly on the battery positive terminal.
- Turn the Key to its ON position but do not start the engine.
- Your multimeter should read battery voltage (11 to 12 Volts).
CASE 1: If the multimeter registered 11 to 12 Volts, then the PCM is feeding a good ground to the TP sensor. The next step is to verify that the TP sensor is creating a good Throttle Position Signal the PCM can use, go to: TEST 3: Testing the TP Signal.
CASE 2: If the multimeter DID NOT register 11 to 12 Volts, then there's a problem with the Ground Circuit, either because there's an open short in the circuit or the PCM is fried.
Altho' testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your Ford vehicle as being the cause of the problem and/or the TPS diagnostic trouble code (DTC) lighting up the check engine light (CEL).
TPS TEST 3: Testing the TP Signal
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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 sensorlightly 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 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.
