How To Test The TPS (1995-2000 4.0L Ford Explorer, Aerostar, And Mercury Mountaineer)

TPS TEST 2: Making Sure The TPS Is Receiving 5 Volts

The throttle position sensor (TPS) on your 4.0L equipped Ford vehicle needs power to work. This power comes in the form of 5 Volts DC from the fuel injection computer.

The terminal that delivers these 5 Volts to the TPS is the one labeled with the number 1 in the photo above.

This test will help you to confirm if these 5 Volts are present or not.

This is what you'll need to do:

1. 1

   Grab your multimeter and select Volts DC mode on it.

2. 2

   Disconnect the connector from the TP sensor.

3. 3

   Probe the brown with white stripe (BRN/WHT) wire with the red multimeter test lead and an appropriate tool (like a wire-piercing probe).
   
   The BRN/WHT wire connects to the female terminal labeled with the number 1 in the photo above.
   
   NOTE: Be careful not to damage the female terminal.

4. 4

   Connect the black multimeter test lead to the negative (-) battery terminal.

5. 5

   When everything is set up, have a helper rotate the key to its ON position but don't start the engine.

6. 6

   The multimeter should display 4.5 to 5 Volts DC.

Let's take a look at what your test results mean:

CASE 1: The multimeter registered 4.5 to 5 Volts. This is the correct test result and it confirms that the fuel injection computer and the wire are supplying the TPS with power.

The next step is to make sure that the throttle position sensor is getting Ground, go to: TPS TEST 3: Making Sure The TPS Is Receiving Ground.

CASE 2: The multimeter DID NOT register 4.5 to 5 Volts. This test result tells you that the TPS is not receiving power. Without these 5 Volts, the TPS will not function.

The two most likely reasons for this are:

• An open-circuit problem in the wire between the TPS connector and the PCM connector.
• The PCM may be fried (very very rare).

Altho' it's beyond the scope of this tutorial to test these two conditions, you have now eliminated the throttle position sensor (TPS) on your Ford 4.0L 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: Making Sure The TPS Is Receiving Ground

So far you've verified that the TPS is not creating a throttle position signal (TPS TEST 1) and that the TPS is getting power (TPS TEST 2).

The second and last step, before condemning the throttle position sensor as bad, is to verify that it's receiving Ground.

The terminal that supplies Ground to the TPS is the one labeled with the number 3 in the photo above.

CAUTION: The fuel injection computer is the one that provides Ground to the TPS. Be careful and don't accidentally or intentionally apply battery power (12 Volts) to this circuit. If you do, you'll fry the PCM.

OK, here are the test steps:

1. 1

   Grab your multimeter and select Volts DC mode on it.

2. 2

   Disconnect the connector from the TP sensor.

3. 3

   Probe the gray with red stripe (GRY/RED) wire with the black multimeter test lead and an appropriate tool (like a wire-piercing probe or a back-probe).
   
   The GRY/RED wire connects to the female terminal labeled with the number 3 in the photo above.
   
   NOTE: Be careful not to damage the female terminal.

4. 4

   Connect the red multimeter test lead to the positive (+) battery terminal.

5. 5

   When everything is set up, have a helper rotate the key to its ON position but don't start the engine.

6. 6

   The multimeter should display 10 to 12 Volts DC.

Let's take a look at what your test results mean:

CASE 1: The multimeter showed 10 to 12 Volts. This the correct test result and it confirms that the TPS is getting Ground. You can also conclude that the PCM and the wire/circuit (that supply this Ground) are OK.

This multimeter test result also confirms that the TPS sensor is bad and needs replacement only if you have confirmed that:

• The TPS is not producing a signal that increases/decreases as the throttle plate opens/closes (TEST 1).
• The TPS has power in the form of 5 Volts DC (TEST 2).
• The TPS has Ground (TEST 3).

If you need to replace the TPS, check out the following section: Where To Buy The TPS And Save.

CASE 2: The multimeter DID NOT show 10 to 12 Volts. This tells you that the TPS is not getting Ground.

This is usually due to a problem with either the PCM (internal fault/problem) or an open-circuit problem in the wire between the TPS and the PCM itself.

Altho' testing these two conditions are beyond the scope of this tutorial, 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 Code Won't Go Away

So you've tested the throttle position sensor (TPS) and according to the test results, the TPS is good, but the check engine light (CEL) keeps coming back on even after you erased the diagnostic trouble code (DTC) from the computer's (PCM) memory. 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 lights up 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 pedal 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've found that the best way to test these intermittent problems 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.