The 1999-2004 4.7L Jeep Grand Cherokee's throttle position sensor (TPS) can be tested using a simple multimeter to see if it's bad (or not). As a matter of fact, you don't need a scan tool! In this tutorial I'll show you how in a step-by-step way.
Contents of this tutorial:
- Symptoms Of A Bad Throttle Position Sensor.
- TEST 1: Testing The Throttle Position Sensor Voltage Signal.
- TEST 2: Verifying Throttle Position Sensor Has Power.
- TEST 3: Verifying Throttle Position Sensor Has Ground.
- Where To Buy Your Throttle Position Sensor And Save.
- More 4.7L Jeep Diagnostic Tutorials.
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:
- 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.
- Your 4.7L Jeep fails the smog check (state mandated emissions test).
- Bad gas mileage.
- Hard start and/or extended cranking time (after shut off).
- Black smoke coming out of the tailpipe.
- 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.
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:
Place your multimeter in Volts DC mode and with 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.
Ground the black multimeter test lead on the battery negative terminal. Have your helper turn the Key On, but don't start the engine (this will power up the TP sensor).
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.
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.
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.
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 4.
OK, now you'll need someone to help you lightly tap on the throttle position sensor with the handle of a screw-driver (or something similar, and I want to emphasize the words ‘lightly tap’) as you slowly open and close the throttle 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.
Repeat step 7 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.