TEST 1: Testing The Throttle Position Signal
The very first thing you'll do, is test to see if the throttle position sensor is creating (and thus sending) a good throttle angle signal to the fuel injection computer.
IMPORTANT: The TPS must remain connected to its electrical connector to be able to read the TPS signal with a multimeter. You'll need to use a back probe or a wire-piercing probe to check for the TPS voltage signal in the wire. You can see an example of this tool here: Wire Piercing Probe.
These are the steps:
Connect the red multimeter test lead to the wire that connects to the terminal labeled with the letter C in the photo.
Ground the black multimeter test lead on the battery negative (-) terminal.
Turn the key on, but don't crank or start the engine.
The multimeter should register about 0.5 to 0.7 Volts DC. If it doesn't, don't worry about it just yet, continue with the other steps.
Slowly open the throttle plate by hand till it's completely open while you eyeball the voltage displayed by the multimeter.
The voltage should increase till it stops at about 4.5 to 4.9 Volts DC (once the throttle plate is fully open) without any skips or gaps in the reading.
Slowly close the throttle plate till completely closed. Your multimeter should show a decreasing voltage till it reaches the voltage you recorded in step 3.
Have your helper lightly tap the TP sensor with the butt of a screw-driver's handle (or something similar, and I want to emphasize the words ‘lightly tap’) as you open and close the throttle plate once again.
The tapping SHOULD NOT have any effect on the voltage readings.
Repeat step 8 several times to make sure of your multimeter test results.
Let's interpret your test result:
CASE 1: The voltage increased and decreased smoothly and without any gaps. This is the correct test result and tells you that the throttle position sensor on your Isuzu (or Honda Passport) is OK and functioning correctly.
No need to continue with the other tests in the article since this result also confirms that the TPS is getting both power and Ground.
If the TPS diagnostic trouble code keeps coming back, take a look at the section: TPS Code Won't Go Away.
CASE 2: The voltage DID NOT increase or decrease smoothly and/or you saw gaps in the voltage reading. This test result tells you that the throttle position sensor is bad. Replace the TPS sensor.
CASE 3: The multimeter registered 0 Volts. Generally this test result tells you that the TPS sensor is bad.
But before you replace the TPS, it's important that you make sure that it's getting 5 Volts and Ground. Continue to the next test: TEST 2: Making Sure The TPS Is Getting 5 Volts.
TEST 2: Making Sure The TPS Is Getting 5 Volts
The throttle position sensor (TPS) on your 3.2L Isuzu Amigo (Rodeo, Trooper, Honda Passport, etc) needs power to work. This power comes in the form of 5 Volts DC from the fuel injection computer.
The test in this section will help you to confirm if these 5 Volts are present or not.
The wire that feeds these 5 Volts to the throttle position sensor is the wire that connects to the terminal labeled with the letter A in the illustration above.
This is what you'll need to do:
Place your multimeter in Volts DC mode.
Disconnect the TPS from its electrical connector.
Connect the red multimeter test lead (with the appropriate tool) to the terminal labeled with the letter A in the image above.
NOTE: If you probe the front of the connector, be careful not to damage the female terminal.
Connect the black multimeter test lead directly on the negative (-) battery terminal.
Have a helper turn the key on, but don't start the engine.
The multimeter should display 4.5 to 5 Volts.
Let's see what your multimeter test result means:
CASE 1: The multimeter registered 4.5 to 5 Volts. This is the correct test result and it confirms that the fuel injection computer and the wire is supplying the TPS with power.
The next step is to test the Ground circuit of the throttle position sensor, TEST 3: Testing The TPS Ground Circuit.
CASE 2: The multimeter DID NOT register 4.5 to 5 Volts. This test result tells you that the computer or the circuit are NOT providing the voltage that the TPS needs to operate. The two most likely reasons for this are: 1) an open-circuit problem in the wire or 2) the PCM may be fried.
Altho' it's beyond the scope of this article to test these two conditions, you have now eliminated the throttle position sensor (TPS) on your 3.2L Isuzu or Honda as being the cause of the problem and/or the TPS diagnostic trouble code (DTC) lighting up the check engine light (CEL).