How To Test The Throttle Position Sensor (1999-2004 4.7L V8 Jeep Grand Cherokee)

The 1999-2004 4.7L Jeep Grand Cherokee's throttle position sensor (TPS) is probably one of the easiest sensors on the engine to test.

Not only that, you can check it with a simple multimeter to see if it's bad (or not). As a matter of fact, you don't need a scan tool or any other fancy (or expensive) diagnostic equipment!

In this tutorial, I'll show you how step by step. You'll quickly find out if the TPS is good or bad, and with your test results, you'll be able to diagnose any of these codes: P0121, P0122, or P0123.

APPLIES TO: This tutorial applies to the following vehicles:

• 4.7L V8 Jeep Grand Cherokee: 1999, 2000, 2001, 2002, 2003, 2004.

MAP SENSOR DIAGNOSTICS:

• How To Test The MAP Sensor (1999-2001 4.7L V8 Grand Cherokee).

Symptoms Of A Bad Throttle Position Sensor

The basic function of the throttle position sensor's create a signal that tells the PCM how much the throttle plate opens/closes as you step ON/OFF the accelerator pedal.

This throttle angle signal is then used by the PCM to calculate fuel injection, advance/retard ignition timing, etc. So when the TPS fails, your 4.7L Jeep Grand Cherokee's engine performance is gonna' suffer.

Here are some of the symptoms, of failed TPS, you may see:

1. A TPS diagnostic trouble code (DTC) lighting up the check engine light:
   • P0121: Throttle Position (TP) Circuit Performance Problem.
   • P0122: Throttle Position (TP) Circuit Low Input.
   • P0123: Throttle Position (TP) Circuit High Input.
2. Your 4.7L Jeep fails the smog check (state mandated emissions test).
3. Bad gas mileage.
4. Hard start and/or extended cranking time (after shut off).
5. Black smoke coming out of the tailpipe.
6. Hesitation when accelerating your vehicle down the road.

Thankfully, the TPS can be tested without a scan tool and in the next section we'll start with the very first test.

Where To Buy Your TP Sensor And Save

The following links will help you to comparison shop for the throttle position sensor:

Not sure if the above TP sensor fits your particular 4.7L equipped Jeep Grand Cherokee? Don't worry, once you get to the site, they'll make sure it fits by asking you the particulars of your vehicle. If it doesn't fit, they'll find you the right one.

TEST 1: Testing The Throttle Position Sensor Voltage Signal

The successfully diagnose the TPS as good or bad, we need to know that:

• The TPS produces a voltage signal.
• This voltage signal increases as the throttle plate opens. At wide-open-throttle (WOT), the TPS produces about 4.5 Volts DC.
• This voltage signal decreases as the throttle plates closes from its open position.
• The wire that carries this TP voltage signal is the orange with red stripe (ORG/RED) wire of the TPS connector.

Using a multimeter, you and I can see these increases/decreases in real time. This is how we're gonna' test it!

NOTE: The throttle position sensor has to remain bolted to the throttle body and connected to its connector for this test to work (this is where a wire piercing probe comes in handy to get to the signal inside the wire. To see what one looks like, click here: Wire Piercing Probe Tool.

OK, let's start:

1. 1

   Place your multimeter in Volts DC mode.

2. 2

   Connect the red multimeter test lead probe the middle wire of the sensor's connector.
   
   This is the wire that connects to TPS terminal #2 in the illustration above.

3. 3

   Ground the black multimeter test lead on the battery negative (-) terminal.

4. 4

   Have your helper turn the key to the ON position, but don't start the engine (this will power up the TP sensor).

5. 5

   Your multimeter should report a voltage between 0.2 to 0.9 Volts DC. If your multimeter doesn't, don't worry about it just yet, continue with the other steps.

Part 2

1. 6

   Now, slowly open the throttle (by hand and from the engine compartment) while you observe the change in voltage numbers on your multimeter.
   
   For this test result to be accurate, you need to open the throttle by hand and not from inside the vehicle.

2. 7

   As the throttle opens, the voltage numbers will increase.
   
   This increase in voltage should be smooth and without any gaps or skips.
   
   Once the throttle is wide open, your multimeter should read somewhere between 3.5 to 4.5 Volts DC.

3. 8

   Now, slowly close the throttle.
   
   As the throttle is closing, you should see the voltage decrease smoothly and without any gaps or skips, to the exact same voltage you noticed in step 5.

Part 3

1. 9

   Lightly tap on the throttle position sensor with the handle of a screw-driver as you slowly open and close the throttle plate and observe the multimeter.
   
   If the TPS is bad, the tapping will cause the voltage numbers to skip or go blank.
   
   If the TPS is OK, the tapping will have no effect on the voltage numbers.

2. 10

   Repeat step 9 several times to make sure of your multimeter test results.

Let's take a look at your test results:

CASE 1: The throttle angle voltage increased and decreased as you opened and closed the throttle plate. This confirms that the throttle position sensor is OK and not defective.

CASE 2: The throttle angle voltage DID NOT increase (and/or decrease) as you opened and closed the throttle plate. This tells you that the TPS is bad and causing the TPS trouble code lighting up the check engine light (CEL) on your 4.7L Jeep Grand Cherokee.

Before you run out and buy it, I'm gonna' suggest that you do two more tests. One is to check that the TPS is getting power. The other is to check that it's Ground. To check that the TPS is getting power, go to: TEST 2: Verifying Throttle Position Sensor Has Power.

CASE 3: The multimeter DID NOT register any voltage. This test result doesn't condemn the TP sensor as bad just yet.

Why? Because the TP sensor may be missing either power or Ground. So the next step is to check that the TP sensor is getting power, go to: TEST 2: Verifying Throttle Position Sensor Has Power.

TEST 2: Verifying Throttle Position Sensor Has Power

If you've reached this point, your multimeter has confirmed that the TPS is not creating an increasing/decreasing throttle position (TP) voltage signal. In some rare cases, this is due to the fact that the TPS is either missing power or Ground. So, in this test step, we're gonna' make sure it's getting power.

The throttle position sensor connector's wire that feeds this power (5 Volts DC) to the TPS is the orange (ORG) wire. This ORG wire connects to TPS terminal #1 in the illustration above.

These are the test steps:

1. 1

   Set your multimeter to Volts DC mode and turn the key on but don't start the engine.
   
   This will power up the TP sensor's connector.

2. 2

   Check the TPS connector's ORG wire with the red multimeter test lead (see the illustration above).
   
   IMPORTANT Avoid probing the front of the TPS connector. Probing the metal terminal of the TPS connector, with your multimeter's test lead, could damage it and require that you replace the connector. Use a back probe or a wire piercing probe instead of probing the front of the connector.

3. 3

   Connect the black multimeter test lead to a good and clean Ground point on the engine or directly on the negative (-) battery terminal.

4. 4

   When you've set up the test, have a helper turn the Key On Engine Off (KOEO).

5. 5

   Your multimeter should display 4.5 to 5 Volts on its screen. OK, now let's interpret your test results below:

CASE 1: Your multimeter confirms that the ORG wire has 4.5 to 5 Volts. This tells you that the TPS connector is feeding the TPS with power.

The next and last test, is to make sure that the throttle position sensor is getting Ground (from the PCM too). For this test, go to: TEST 3: Verifying Throttle Position Sensor Has Ground.

CASE 2: Your multimeter confirms that the ORG wire DOES NOT have 4.5 to 5 Volts. Double check that you're testing the correct connector terminal and repeat the test.

If your multimeter still doesn't show the 4.5 to 5 Volts DC, then this test result tells you that the reason the TPS is not creating a proper TP voltage signal (in TEST 1) is due to a lack of power.

Since the PCM provides this power, the most likely culprit is an open in the ORG wire between the TPS connector and the PCM connector. Although beyond the scope of this tutorial, your next step is to diagnose and restore this missing power.

TEST 3: Verifying Throttle Position Sensor Has Ground

In this last test, you're gonna' make sure that the TPS is being fed Ground. Ground is fed by the black with light blue stripe (BLK/LT BLU) wire. The BLK/LT BLU wire is the one that connects to TPS pin #3.

To check for the availability of Ground, you'll do a simple voltage test with your multimeter very much like the one you did in TEST 2.

IMPORTANT: Ground is provided directly by the fuel injection computer. Be careful and don't intentionally or accidentally short this wire (circuit) to battery power or you'll fry the fuel injection computer.

OK, here are the test steps:

1. 1

   Set your multimeter to Volts DC mode.

2. 2

   Probe the TPS connector's BLK/LT BLU wire with the black multimeter test lead.
   
   Avoid probing the front of the TPS connector. Probing the metal terminal of the TPS connector with the multimeter test lead could damage it (and require that you replace the connector). Use a back probe or a wire piercing probe instead of probing the front of the connector.

3. 3

   Now, with the red multimeter test lead, probe the battery positive (+) terminal.

4. 4

   Turn the key to its ON position but don't start the engine. This will power up the fuel injection computer.

5. 5

   Your multimeter will display 11 to 12 Volts if terminal B is feeding the TPS with Ground.

   
   

CASE 1: The multimeter showed 10 to 12 Volts. This is the correct and expected test result and confirms the TPS is getting Ground.

You can conclude that the TPS is bad only if you have confirmed that:

1. The TP sensor is not creating an increasing/decreasing voltage signal when manually opening/closing the throttle plate (TEST 1).
2. The TP sensor is being fed 5 Volts DC (TEST 2).
3. The TP sensor is being fed Ground (TEST 3).

Taking the 3 test results above, you can conclude that the throttle position sensor is bad and needs to be replaced (and that this will solve the TP sensor code lighting up the check engine light).

When you're ready to replace the TPS, I recommend the following from brands I've used in the field and recommend:

• Standard Motor Products TH190T Throttle Position Sensor (Amazon affiliate link).
• A-Premium TPS Throttle Position Sensor (Amazon affiliate link).

CASE 2: Multimeter DID NOT show 10 to 12 Volts. Double check that you're testing the correct connector terminal and repeat the test.

If your test result still indicates that the TPS is not getting Ground, then we can conclude that one of two things are causing this lack of Ground:

1. There's an open in the BLK/LT BLU wire between the TP sensor connector and the fuel injection computer's connector.
2. The fuel injection computer has an internal problem (although this is extremely rare).

Although testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your 4.7L Jeep Grand Cherokee as being the cause of the problem and/or the TP sensor diagnostic trouble code (DTC) lighting up the check engine light (CEL).

More 4.7L V8 Jeep Grand Cherokee Diagnostic Tutorials

You can find a complete list of 4.7L Jeep tutorials in these two indexes:

• 4.7L V8 Jeep Grand Cherokee Index Of Articles.