TPS TEST 2: Verifying TPS Has Power

How To Test A P0123 Diagnostic Trouble Code (Honda 2.2L, 2.3L)

If your TP sensor did not show a variable voltage when you manually actuated the throttle in TPS TEST 1, then the next step is to make sure it's being fed with power.

The wire labeled with the number 3, in the illustrations in the image viewer, is the one that carries these 5 Volts from the PCM to the TP sensor.

In this test section, we'll test for the presence of these 5 Volts using a multimeter.

NOTE: You can test for these 5 Volts DC with the TP sensor connected or disconnected to the TPS. I personally prefer to do this test with the TP sensor's connector unplugged.

This is what you'll need to do:

  1. 1

    Set your trusty multimeter's dial to Volts DC mode.

  2. 2

    Probe the number 3 wire, with the red multimeter test lead and an appropriate tool (like a Wire-Piercing Probe). The throttle position sensor's connector can be connected to the sensor or not when you probe this circuit.

    IMPORTANT If you probe the front of the TPS connector, be careful and don't damage the terminal. Damaging the terminal will require that you replace the connector.

  3. 3

    Connect the black multimeter test lead to a good and clean ground point on the engine or directly on the negative (-) battery terminal.

  4. 4

    When you've set up the test, have a helper turn the Key On Engine Off (KOEO).

  5. 5

    Your multimeter should display 4.5 to 5 Volts on its screen. OK, now let's interpret your test results below:

CASE 1: multimeter registered 4.5 to 5 Volts, this confirms that the TP sensor is being fed with power (4.5 to 5 Volts DC).

The next step is to test the ground circuit of the throttle position sensor, go to TPS TEST 3: Verifying TPS Has Ground.

CASE 2: multimeter DID NOT register 4.5 to 5 Volts, Recheck your connections and repeat the test. If your multimeter still doesn't register the 4.5 to 5 Volts DC...

... then you've just eliminated the TP sensor itself as bad. The two most likely reasons for this are: 1) an open short in the circuit or 2) the PCM may be fried (althoug a bad PCM is very rare).

Although it's beyond the scope of this article to test these two conditions, you have now eliminated the throttle position sensor (TPS) on your Honda as being the cause of the problem and/or the TPS diagnostic trouble code (DTC) lighting up the check engine light (CEL).

TPS TEST 3: Verifying TPS Has Ground

How To Test A P0123 Diagnostic Trouble Code (Honda 2.2L, 2.3L)

The TP sensor connector wire labeled with the number 1, in the illustration in the image viewer, is the one that supplies ground to the sensor.

In this last test... we'll be using the multimeter in Volts DC mode to check that this circuit is providing the throttle position sensor (TPS) a good path to ground.

IMPORTANT: Remember, the PCM is the one that provides this ground internally... so be careful and don't accidentally or intentionally apply power (12 Volts) to this circuit or you'll fry the PCM.

OK, here are the test steps:

  1. 1

    With your multimeter still in Volts DC mode from TPS TEST 2.


  2. 2

    Probe the wire labeled with the number 1 in the photos with the black multimeter test lead. The TPS connector can be connected or not to the Sensor.

    It's important that you do not probe the front of the connector or you run the risk of damaging the terminal.

  3. 3

    Now, with the red multimeter test lead, probe the battery positive (+) terminal.

  4. 4

    Once again, when everything is ready, have your helper turn the Key to its ON position but don't start the engine.

  5. 5

    If this circuit is OK and the PCM is providing a good path to ground, your multimeter will display 11 to 12 Volts.


CASE 1: multimeter showed 11 to 12 Volts, this confirms that the PCM and the wire/circuit (that supply this ground) are OK.

All three test have confirmed that:

  1. The TPS is not providing a varying voltage signal when manually opening the throttle plate.
  2. The TPS is being fed 5 Volts DC.
  3. The TPS is being fed ground.

Therefore, you can conclude that the TP Sensor is BAD and needs to be replaced.


CASE 2: Multimeter DID NOT show 11 to 12 Volts, Recheck your connections and repeat the test. If your multimeter still doesn't show the indicated voltage...

...then this indicates a problem with either the PCM (internal fault/problem) or an open in the wire between the TPS and the PCM itself.

Although testing these two conditions are beyond the scope of this article, you have now eliminated the throttle position sensor (TPS) on your Honda as being the cause of the problem and/or the TPS Diagnostic Trouble Code (DTC) lighting up the check engine light (CEL).