TPS TEST 2: Verifying The TPS Has Power

How To Test A P0122 Diagnostic Trouble Code (Honda 2.2L, 2.3L)

As mentioned at the beginning of this tutorial, the TP sensor on your Honda needs power to function.

The PCM feeds the TP sensor this power in the form of 5 Volts DC and thru the wire labeled with the number 3 in the illustrations in the image viewer.

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

    Grab your multimeter and select Volts DC mode on it.

  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.

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

  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 everything is set up, have a helper rotate the Key to its ON position but don't start the engine.

  5. 5

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

CASE 1: The multimeter registered 4.5 to 5 Volts. This confirms that your Honda's fuel injection computer and the circuit is supplying the TPS with power.

The next step is to test the Ground circuit of the Throttle Position Sensor, go to: TPS TEST 3: Verifying The TPS Has Ground.

CASE 2: The 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-circuit problem in the circuit or 2) the PCM may be fried.

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 The TPS Has Ground

How To Test A P0122 Diagnostic Trouble Code (Honda 2.2L, 2.3L)

So far you have verified that the TPS is not creating a throttle position signal (TPS TEST 1) and that the TPS is getting power (TPS TEST 2).

The last test, before condemning the throttle position sensor, is to verify that your Honda's PCM is feeding it 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.

Let's take a look at your test results:


CASE 1: The multimeter showed 11 to 12 Volts. Then the PCM and the wire/circuit (that supply this Ground) are OK.

Since you have now verified the following:

  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.

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

CASE 2: The 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-circuit problem 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).