TEST 2: Verifying Throttle Position Sensor Has 5 Volts And Ground
If in TEST 1, the TP signal wire did not show any voltage or had a voltage that was stuck in one value, the next step is to make sure that the sensor is getting power and Ground. Power is in the form of 5 Volts DC. Both these 5 Volts DC and Ground are provided by the fuel injection computer.
Verifying their presence involves another set of simple multimeter voltage tests.
These are the test steps:
Verify that the wire labeled with the #1 (in the photo) has 4.5 to 5 Volts with the key on but engine off. This is usually a brown with white stripe (BRN/WHT) wire.
Connect the red multimeter test lead (using the appropriate tool) to the wire labeled with the #1. Connect the black multimeter test lead to the negative (-) battery terminal.
Your multimeter should read 4.5 to 5 Volts DC.
Verify that the wire labeled with the #3 (in the photo) has Ground with the key on but engine off. This is usually a gray with red stripe (GRY/RED) wire.
Connect the black multimeter test lead (using the appropriate tool) to the wire that connects to the wire labeled with the #3 of the TPS connector. Connect the red multimeter test lead to the positive (+) battery terminal.
Your multimeter should read 10 to 12 Volts DC.
Let's take a look at what your test results mean:
CASE 1: Your multimeter confirms that 5 Volts and Ground are being fed to the TPS. This is the correct and expected test result.
You can conclude that the TPS, on your 4.0L Ford, is bad only if all tests have confirmed that:
- The TP sensor IS NOT providing a varying voltage signal when manually opening/closing the throttle plate.
- The TP sensor is being fed 5 Volts DC.
- The TP sensor is being fed ground.
CASE 2: Power or Ground are not present. Double check your connections and make sure that you're testing the correct wires. If your multimeter still does not show power and/or ground...
...then you can conclude that there's an open in the wiring between the TP sensor harness connector and the PCM's harness connector. In the extreme of cases, the PCM has an internal problem (although this is very rare).
Although testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) as being the cause of the problem and/or the TP sensor diagnostic trouble code (DTC) lighting up the check engine light (CEL).
Where To Buy The TPS And Save
The following links will help you to comparison shop for the 1990-1994 4.0L Ford TPS. I think they'll save you a few bucks:
Not sure if the above TPS fits your particular 4.0L Ford Explorer (Aerostar or Ranger)? Don't worry, once you get to the site they'll make sure it fits by asking you the specifics of your particular Ford vehicle. If it doesn't fit, they'll find you the right one.
If this info really saved the day, buy me a beer!