How To Test The Isuzu 3.2L Throttle Position Sensor (3.2L Isuzu Amigo, Rodeo, and Trooper, 3.2L Honda Passport)

This article will help you to diagnose a BAD throttle position sensor on your 3.2L 93-99 Isuzu Amigo, Rodeo, Trooper or Honda Passport.

This is a simple multimeter test that's done in Volts DC mode. No Scan Tool's required.

To help you navigate this article a little easier, here are its contents at a glance:

  1. Important Tips And Suggestions.
  2. Symptoms Of A BAD TPS.
  3. How Does the Throttle Position Sensor Work?
  4. TEST 1: Testing The Throttle Position Signal.
  5. TEST 2: Checking The 5 Volt Feed Circuit.
  6. TEST 3: Testing The TPS Ground Circuit.
  7. TPS Code Won't Go Away.

Important Tips And Suggestions

TIP 1: The most effective way to test the throttle position sensor on your Isuzu is to test it while the engine is at normal operating temperature. So, if the engine is cold, on your Isuzu, crank up the engine and let it warm up for about 20 minutes.

TIP 2: All three of the wires that come out of the throttle position sensor connect directly to the Fuel Injection Computer... so you have to be very careful not to short these to 12 Volts, or you'll fry the computer.

TIP 3: You can use a digital or an analog multimeter. Both will work.

Symptoms Of A BAD TPS

You'll have the CHECK ENGINE LIGHT on, for sure, on your instrument cluster and one of several of the following symptoms:

  1. TPS diagnostic trouble codes (DTCs) stored in the vehicle's computer's memory.
    1. P0121: Throttle Position (TP) Sensor Circuit Performance.
    2. P0122: Throttle Position (TP) Sensor Circuit Performance/Low Voltage.
    3. P0123: Throttle Position (TP) Sensor Circuit Performance/High Voltage.
  2. Really BAD gas mileage. You know that it's not the price of gasoline that has you thinking that your Isuzu 3.2L (or 3.2L Honda Passport) is costing you more at the pump.
  3. Transmission does not shift out of second gear. Now, this doesn't happen very often, but it happens.
  4. No power and/or hesitation as you accelerate the vehicle. It feels like all of a sudden someone cut the power out momentarily as you step on the gas to get the vehicle moving.

How Does the TPS Work?

Circuit Descriptions Of The TPS (3.2L Isuzu Rodeo)

In a nutshell, this is how the throttle position sensor Works:


  1. When you turn the Key to the On position and then start the engine, the TPS gets power thru' the wire labeled with the letter A.
    1. This power is in the form of 5 Volts.
    2. These 5 Volts are provided by the PCM.
  2. Ground is provided by the Fuel Injection Computer thru' the circuit labeled with the letter B.
  3. Now, the accelerator cable connects to the throttle on the engine. The throttle position sensor is bolted to the throttle body in a position where it can measure the amount the throttle opens and closes (as you step on or release the accelerator pedal).
  4. So then, when you accelerate the engine, the throttle plate opens and the TPS immediately measures this and sends this info to the Fuel Injection Computer. This is accomplished thru' the wire labeled with the letter C.
  5. Now, when you let go of the accelerator pedal, the throttle closes and always the alert sentinal, the TPS keeps feeding this change to the Fuel Injection Computer.
  6. The Fuel Injection Computer uses this info (that the TPS provides) to control Fuel Injection, Ignition Advance and host of other things to keep your engine running smoothly.

Testing the TPS, to see if it's bad or not, simply involves making sure it's getting power and ground and that it's creating a throttle plate position signal.

Alright, let's get testing in the next couple of pages...