The throttle position sensor on your 1997 thru' 2001 3.0L Mitsubishi Montero is two sensors in one. By this I mean that the TPS assembly has two parts that perform two specific functions. One part of the TPS assembly is a throttle position sensor. The other part is a closed throttle position switch.
In this tutorial, we're gonna' test the throttle position sensor part of the TPS assembly. This is a pretty simple test that can be easily be done with a multimeter.
The contents of this tutorial at a glance:
- 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.
Symptoms Of A Bad Throttle Position Sensor
When the throttle position sensor (TPS) fails, your Montero's PCM will set a diagnostic trouble code. Here's a basic list of symptoms you'll see:
- Check engine light (CEL) is illuminated on your Montero's instrument panel.
- A TPS diagnostic trouble code (DTC) stored in the PCM's memory:
- P0120: Throttle Position Sensor Circuit Malfunction.
- 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.
TEST 1: Testing The Throttle Position Sensor Voltage Signal
The throttle position sensor's job is to report the angle of the throttle plate. In a nutshell, when the throttle plate is closed the TPS reports a low voltage and as it opens the TPS reports a higher voltage.
When the TPS fails, it'll usually just stop reporting the increases/decreases in this throttle angle voltage. The cool thing is that you and I can check this throttle angle voltage signal with a multimeter (no scan tool is needed).
The wire that carries this throttle angle voltage signal to the PCM, and which we'll tap into, is the wire that connects to TPS pin #3 (in the illustration above).
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.)
OK, let's start:
Place your multimeter in Volts DC mode and with the RED multimeter lead probe the middle wire of the sensor's connector. This is the wire that connects to TPS pin #3 in the illustration above.
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 a voltage between .2 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: The voltage increased/decreased as you manually opened/closed the throttle plate. This test result confirms that the TP sensor is OK and not defective.
CASE 2: The voltage DID NOT increase/decrease as you manually opened/closed the throttle plate. This tells you that the throttle position sensor (TPS) on your Montero has a problem.
Before condemning the TPS to the scrap heap, you need to make sure that it's getting both power and ground. To check for power, go to: TEST 2: Verifying Throttle Position Sensor Has Power.
CASE 3: 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.