How To Test The TPS (1993-1994 3.0L Ford Ranger)

TEST 2: Making Sure The TPS Is Getting 5 Volts And Ground

In this section, we're gonna' make sure that you are Ford Ranger's TPS is getting 5 Volts and Ground.

Both the 5 Volts and Ground are provided by your Ford Ranger's fuel injection computer.

The wire that feeds 5 Volts to the TPS is the brown with white stripe (BRN/WHT) wire of the connector. This BRN/WHT wire connects to the terminal identified with the number 3 in the illustration above.

The wire that feeds Ground to the TPS is the grey with red stripe (GRY/RED) wire of the connector. This GRY/RED wire connects to the terminal identified with the number 3 in the illustration above.

NOTE: Be very careful to not short the Ground wire to battery 12 Volts or you will fry your Ford Ranger's fuel injection computer. The voltage test indicated in the test steps below is a very safe way to test the Ground circuit.

These are the test steps:

1. 1

   Check the BRN/WHT wire for power with the Key On Engine Off (KOEO) (see illustration above).
   
   Back probe the wire that connects to terminal number 3 with the red multimeter test lead and connect the black lead to the battery negative (-) post.
   
   The multimeter should register 4.5 to 5 Volts DC.

2. 2

   Check the GRY/RED wire for Ground with the Key On Engine Off (KOEO) (see illustration above).
   
   Back probe the wire that connects to terminal number 1 with the black multimeter test lead and connect the red lead to the battery positive (+) post.
   
   The multimeter should register battery voltage (12+ Volts).

Let's interpret your test results:

CASE 1: The TPS is getting 5 Volts and Ground. This is the correct test result.

Taking into account that you've reached this point because the TPS did not pass the test in TEST 1 and that it is getting 5 Volts and Ground, you can now correctly conclude that the TPS on your Ford Ranger is defective. Your next step is to replace the throttle position sensor.

CASE 2: The TPS is not getting 5 Volts or Ground. Without 5 Volts or Ground the throttle position sensor will not work.

The next step is to find out why power or Ground is missing and resolve the issue. I can tell you from personal experience that usually what causes this to happen is an open circuit in the wires between the fuel injection computer and the TPS connector.

TPS Trouble Code Won't Go Away

Every now and then you'll see a case where the TPS is working correctly (or its brand new), yet the fuel injection computer keeps saying it's defective (or that there is a problem in its circuits). If this is the case in your particular situation, then I think the following suggestions will help you in furthering your troubleshooting efforts:

1. Make sure that the throttle position sensor connector isn't damaged. The most common type of connector problem is the is that the is that the that it's locking times are broken. So when the engine starts to vibrate the connector makes a false contact with TPS itself.
2. Make sure that the idle stop screw, on the throttle body, is at its correct adjustment (the arrow in the photo above points to it). In these older vehicles, it's very common thing to see that the idle-stop screw has been adjusted to up the engine RPM at idle. And this adjustment will usually cause fuel injection computer to set a TPS trouble code.
3. Check the continuity of the three wires between the TP sensor connector and the fuel injection computer. This test will help you to find out if there is an open or a short circuit between the TPS and the fuel injection computer.
4. Check that the fuel injection computer isn't defective. Although this can seem quite impossible for the do-it-yourselfer, this is how you can do it:
   1. Eliminate the TPS itself as defective.
   2. Eliminate and open circuit or a short circuit in the wiring between the TPS and the fuel injection computer.
   3. Confirm that the fuel injection computer's Ground circuits are okay. In other words: the computer is getting plenty of Ground through its Ground wires.
   4. Make sure that the fuel injection computer is getting power on all of its power circuits.
   5. If all of the above diagnostic tests pass with flying colors, then more than likely you've got a bad fuel injection computer on your hands.