The throttle position sensor (TPS) on your 1993-1995 Jeep Grand Cherokee can be accurately tested with a simple multimeter to find out if it's bad (or not).
Also, you don't have to remove it to test it and no scan tool is required for the test. In this tutorial I'll show you just how.
Contents of this tutorial:
To see the TP sensor's wiring diagram go to: 1993-1995 TP Sensor Wiring Diagram (Jeep Grand Cherokee 4.0L).
For the TPS on 1996 and newer Grand Cherokee, go to: How To Test TPS Codes: P0121, P0122, P0123 (1997-2001 Jeep 4.0L).
You can find this tutorial in Spanish here: Cómo Probar el Sensor TPS (1993-1995 4.0L Grand Cherokee) (at: autotecnico-online.com).
Symptoms Of A Bad Throttle Position Sensor (TPS)
The throttle position sensor (TPS) is one of the key components your Jeep's powertrain control module (PCM) uses to calculate the correct amount of fuel to inject into the engine (among several things). So, when the TPS fails, your Jeep is gonna' resent it and let you know right away something is amiss.
When the throttle position sensor (TPS) fails, you'll see one or more of the following symptoms:
- Check engine light (CEL) shining nice and bright.
- Diagnostic trouble codes (DTC) stored in the PCM's memory:
- 24: TP Sensor Voltage Low.
- 24: TP Sensor Voltage High.
- Your Jeep Grand Cherokee fails the 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 Jeep down the road.
TEST 1: Testing The TPS Voltage Signal
To get your TPS diagnostic on its way, you first need to identify ORG/DK BLU (orange w/ dark blue stripe) wire of the sensor's 3 wire connector.
The ORG/DK BLU wire is the middle wire of the connector and is the one that carries the throttle angle voltage signal, the TPS creates (and it's the one we're gonna' tap into with a multimeter).
When the throttle position sensor (TPS) fails, it'll fail in one of two ways. It'll either stop producing a throttle angle signal.. which usually means it'll stay stuck at a certain voltage value. Or the TPS will fail intermittently.
The test below will help you check for both types of failures.
NOTE: To ensure the accuracy of your test, my suggestion is to test the throttle position sensor (TPS) with a warmed up engine (but not running).
OK, let's start:
Place your multimeter in Volts DC mode and with the red multimeter test lead probe the wire labeled with the number 2 in the illustration above. This is the circuit that supplies the TP Signal to the PCM.
If you don't have a multimeter or need to upgrade yours, check out my recommendation: Abe's Multimeter Recommendation (found at: easyautodiagnostics.com).
NOTE: The throttle position sensor has to remain 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.)
Ground the black multimeter test lead on the battery negative terminal. Have you helper turn the Key On, but don't start the engine (this will power up the TP sensor).
Your multimeter should report .4 to .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: Multimeter registered a smooth increase or decrease in voltage with no gaps. This tells you several important things. First, that the TP sensor is working like it should. Lastly, that the TP sensor is getting power (5 Volts DC) on the VIO/WHT wire and ground on the BLK/LT BLU wire of the TP sensor connector.
No further testing is required.
CASE 2: Multimeter DID NOT register a smooth increase or decrease in voltage, in other words, it stayed stuck in one voltage value as you opened and closed the throttle plate, then this tells you that the sensor is bad and needs to be replaced.
If I where in your shoes, I would still make sure that the TP sensor is getting both power and ground. To check for power on the VIO/WHT wire, go to: TEST 2: Verifying TPS Has Power.
CASE 3: Multimeter DID NOT register any voltage, this test result doesn't condemn the TPS as BAD just yet. Why? Because...
... the TPS may be missing either power or ground. So the next step is to check that the TPS is getting power, go to TEST 2: Verifying TPS Has Power.