TEST 2: Testing The TPS Voltage Signal
For our second test, we're gonna check the TPS signal output by manually opening and closing the throttle plate.
The test result that'll tell us the TPS is OK, is a TPS signal voltage that increases as we open the throttle plate and decreases as we close the throttle plate.
As in TEST 1, we're going to check this TPS voltage output on the GRY/WHT wire that I've labeled with the number 2.
IMPORTANT: The throttle position sensor must remain connected to its connector in order to access the signal in the wire. You'll need to use a back-probe on the connector or a wire-piercing probe on the wire. You can see what this tool looks like and where to buy it here: Wire Piercing Probe.
Let's get started:
- 1
Place your multimeter in Volts DC mode.
- 2
Connect the red multimeter test lead to the grey with white stripe (GRY/WHT) wire of the TP sensor harness connector.
I've labeled the GRY/WHT wire with the number 2 in the photo above.
NOTE: The TPS must remain connected to its connector to test the TPS voltage signal. - 3
Connect the black multimeter test lead directly on the battery negative (-) post.
- 4
Turn the key on but don't crank or start the engine.
- 5
Manually rotate the throttle plate to its open position.
You'll get the best results by opening and closing the throttle plate directly on the throttle body instead of stepping on the accelerator pedal. - 6
The multimeter should show an increasing voltage as you (or your helper) open up the throttle plate.
- 7
Close the throttle plate as you observer the multimeter.
- 8
The multimeter should show a decreasing voltage as you begin to close the throttle plate.
- 9
Using a screwdriver's handle, gently tap the TP sensor as you open and close the throttle plate and observe the multimeter.
The purpose (of tapping the TP sensor with the screwdriver's handle) is to see if the TP sensor shows gaps in the voltage signal. Why? Because a good TP sensor will show a continuous increasing or decreasing voltage signal even while getting tapped by the screw-driver's handle.
Let's analyze your test results:
CASE 1: The TPS voltage signal increased/decreased as you opened/closed the throttle plate. This is the correct test result and it indicates that the throttle position sensor is good.
With this test result you can also conclude that the TPS sensor is getting both power (5 Volts) and Ground from the fuel injection computer.
CASE 2: The TPS voltage signal DID NOT increase/decrease as you opened and closed the throttle plate. This test result usually indicates that the TPS sensor is defective.
To make sure the TPS sensor is bad the next step is to check that the BRN/WHT wire is feeding the TPS with 5 Volts. For this test go to: TEST 3: Making Sure The TPS Is Receiving 5 Volts.
CASE 3: The multimeter DID NOT register any voltage. This test result usually indicates that the TPS sensor is defective.
To make sure the TPS sensor is bad the next step is to check that the BRN/WHT wire is feeding the TPS with 5 Volts. For this test go to: TEST 3: Making Sure The TPS Is Receiving 5 Volts.
TEST 3: Making Sure The TPS Is Receiving 5 Volts
In this test section, we're going to check that the throttle position sensor is getting power, which is in the form of 5 Volts DC and are provided by the fuel injection computer.
The wire that delivers these 5 Volts is the one that I've labeled with the number 1 in the photo above. This is the brown with white stripe (BRN/WHT) wire of the TPS 3-wire connector.
If the TPS is receiving power, your multimeter should register a voltage between 4.5 to 5 Volts DC.
Let's get testing:
- 1
Disconnect the TPS from its electrical connector.
- 2
Place your multimeter in Volts DC mode.
- 3
Connect the black multimeter test lead to the negative (-) battery terminal.
- 4
Turn the key the ON position but don't start the engine.
- 5
With the red multimeter test lead, gently probe the female terminal that connects to the brown with white stripe (BRN/WHT) wire of the TPS connector.
I've labeled the BRN/WHT wire with the number 1 in the photo above. - 6
Your multimeter should read 4.5 to 5 Volts DC.
Let's analyze your test results:
CASE 1: The BRN/WHT wire is feeding the TPS with 5 Volts. This is the correct test result.
Now that you have confirmed the TPS is getting 5 Volts, the next step is to make sure it's getting Ground. Go to: TEST 4: Making Sure That The TPS Is Receiving Ground.
CASE 2: The BRN/WHT wire IS NOT feeding the TPS with 5 Volts. Without these 5 Volts the TPS will not function.
These missing 5 Volts are usually the result of an open-circuit problem in the BRN/WHT wire between the TPS sensor's connector and the fuel injection computer's connector.
TEST 4: Making Sure That The TPS Is Receiving Ground
Up to this point you have:
- Checked the TPS voltage output with the key on engine off (TEST 1).
- Confirmed that the TPS signal does not increase/decrease as you open/close the throttle plate (TEST 2).
- Confirmed that the TPS is getting 5 Volts (TEST 3).
In this last test section, we're going to check that the TPS is getting Ground. As with the 5 Volts, this Ground is provided by the fuel injection computer.
The wire that delivers Ground to the TPS is the one I've labeled with the number 3 in the photo above and it'll be the grey with red stripe (GRY/RED) wire of the 3-wire connector.
IMPORTANT: Be careful not to short the Ground wire to battery power, or you'll fry the fuel injection computer. The multimeter voltage test suggested below (to test the Ground circuit) is a safe and accurate test.
These are the test steps:
- 1
Disconnect the TPS from its electrical connector.
- 2
Place your multimeter in Volts DC mode.
- 3
Connect the red multimeter test lead to the positive (+) battery terminal.
- 4
Turn the key the ON position but don't start the engine.
- 5
With the black multimeter test lead, gently probe the female terminal that connects to the grey with red stripe (GRY/RED) wire of the TPS connector.
I've labeled the GRY/RED wire with the number 3 in the photo above. - 6
Your multimeter should read 10 to 12 Volts DC.
Let's analyze your test results:
CASE 1: The GRY/RED wire is feeding Ground to the TPS. This is the correct test result.
You can correctly conclude that the TPS is defective if you have:
- Checked the TPS voltage output with the key on engine off (TEST 1).
- Confirmed that the TPS voltage signal does not increase/decrease as you opened/closed the throttle plate (TEST 2).
- Confirmed that the TPS is getting 5 Volts (TEST 3).
- Confirmed, in this test section, that the TPS is getting Ground.
CASE 2: The GRY/RED wire IS NOT feeding Ground to the TPS. Without Ground the TPS will not function.
This missing Ground is usually caused by an open-circuit problem in the GRY/RED wire between the throttle position sensor's connector and the fuel injection computer's connector.
More 4.2L Ford E150 And E250 Test Tutorials
If this tutorial was helpful, be sure and take a look at all of the 4.2L V6 E150 and E250 diagnostic tutorials in this index:
Here's a sample of the tutorials you'll find there:
- How To Test Engine Compression (1997-2003 4.2L V6 Ford E150, E250).
- How To Test The Fuel Pump (1997-2000 4.2L V6 Ford E150, E250).
- How To Test The CKP Sensor With A Multimeter (1997-2003 4.2L V6 Ford E150, E250).
- How To Test For A Blown Head Gasket (1997-2003 4.2L V6 Ford E150, E250).
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