How to Test the Throttle Position Sensor (Honda 1.5L, 1.6L)

source : http://troubleshootmyvehicle.com/honda/1.5L-1.6L/how-to-test-the-tps-sensor-1

Testing the throttle position sensor (TPS) to see if it has failed and causing a TPS diagnostic trouble code (DTC) is not hard.
As a matter-o'-fact, to test the TPS on your Honda Civic, you don't need a scan tool. In this tutorial, I'm gonna' show you how troubleshoot the throttle position sensor (TPS), on your Honda Civic, with a multimeter and in a step-by-step way.
Here are the contents of this tutorial at a glance:

  1. Symptoms of a Bad Throttle Position Sensor (TPS).
  2. How the Throttle Position Sensor (TPS) Works.
  3. Circuit (Wire) Descriptions of the TPS.
  4. START HERE: Troubleshooting the TP Sensor.
  5. TPS TEST 1: Testing the TPS Voltage Signal.
  6. TPS TEST 2: Verifying TPS Has Power.
  7. TPS TEST 3: Verifying TPS Has Ground.
  8. Where to Buy Your TP Sensor and Save.
  9. More Honda 1.5L, 1.6L Test Tutorials.

Symptoms of a Bad Throttle Position Sensor (TPS)

Your Honda Civic's PCM can't live without the input the throttle position sensor provides about throttle plate angle... so, when it receives a TP signal that doesn't square with actual engine operating conditions... your Civic is just not gonna' run right.
You'll see one or more of the following symptoms:
  1. Check engine light (CEL) shining nice and bright.
  2. Diagnostic trouble codes (DTC) stored in the PCM's memory:
    1. P0121: TP Sensor Circuit High Voltage.
    2. P0122: TP Sensor Circuit Low Voltage.
    3. P1121: TP Sensor Signal Lower Than Expected .
    4. P1122: TP Sensor Signal Higher Than Expected.
  3. Your Honda Civic fails the state mandated emissions test.
  4. Bad gas mileage.
  5. Hard start and/or extended cranking time (after shut off).
  6. Black smoke coming out of the tailpipe.
  7. Hesitation when accelerating your Civic.
In the next subheading we'll find out how the TPS works on your Honda Civic.


How the Throttle Position Sensor Works

Your Civic's PCM uses several sensor inputs to control the fuel system, ignition system, and automatic transmission (to name a few). Among those sensor inputs, is the information that the throttle position sensor (TPS) provides about throttle plate angle.
As you might already be aware, the accelerator pedal is connected, via a physical cable (accelerator cable) to the throttle plate on the throttle body.
As you step on and off the accelerator pedal, the throttle plate opens and closes. It's the throttle position sensor's function to measure the amount that the throttle plate opens and closes (throttle angle). It then sends this info to the PCM (Powertrain Control Module = Fuel Injection Computer) as a volt DC signal.
To give you a few more specifics:

  1. As you step on the accelerator pedal,
    1. The throttle plate opens and the TP sensor measures how much and relays this to the PCM.
    2. The fuel injection computer injects more fuel.
  2. As you let your foot off the accelerator pedal,
    1. The throttle plate closes and the TP sensor measures how much and relays this to the PCM.
    2. The fuel injection computer injects less fuel.


Circuit (Wire) Descriptions of the TPS

The throttle position sensor (TPS) on your Honda Civic is located on the side of the throttle body.
If you've already located it... you can see that the TP sensor connector has 3 wires (circuits) coming out of it.
Each wire has a specific job to do. By this I mean each wire carries a specific type of signal to or from the TPS to the PCM.
To better understand how we're gonna' test the throttle position sensor (TPS), in this tutorial, I'm going to briefly describe each wire's job and how the sensor works.
Don't worry... it's nothing too technical and it's all in plain English:
  1. The TP sensor is a 3 wire sensor.
    1. Wire labeled with the number 1.
      1. Feeds ground to the TP sensor.
      2. Ground is provided by the PCM (internally).
    2. Wire labeled with the number 2.
      1. Feeds the throttle angle voltage signal to the PCM.
      2. This voltage signal varies depending on the amount of throttle plate opening.
    3. Wire labeled with the number 3.
      1. Feeds power to the TP sensor.
      2. In the form of 5 Volts DC and is supplied only with Key On Engine Off (KOEO) or Key On Engine Running (KOER).
      3. Power comes directly from the PCM.
  2. The TP sensor is a potentiometer. Its resistance changes in response to changes in the throttle plate's angle.
    1. With throttle closed, a small voltage is create and sent to the PCM.
      1. At closed throttle the TP sensor outputs about .5 Volts DC.
    2. With throttle open to wide open, a bigger voltage is created and sent to the PCM.
      1. At wide open throttle the TP sensor outputs about 4.5 Volts DC.
REMEMBER: The throttle position sensor (TPS), at closed throttle, produces a low voltage signal of around .5 Volts DC. As the throttle plate starts to open (as you step on the accelerator pedal and accelerate the engine), this .5 Volt signal starts to increase. At wide open throttle, the TP sensor will output about 4.5 Volts DC.
With this bit of information, let's move on to the next subheading...



START HERE: Troubleshooting the TP Sensor

The key to diagnosing the your Honda Civic's throttle position sensor (TPS) is to remember that:
  1. The TP sensor's voltage signal increases when the throttle plate opens
  2. The TP sensor's voltage decreases when the throttle plate closes.
So, the absolute best way to find out if the TPS has failed on your Civic is by manually testing the TP sensor with a multimeter (while it's still on the throttle body and connected to its electrical connector).
Here's a summary of the 3 tests in this tutorial:

  1. Check the TP sensor's voltage signal with a multimeter.
    1. You'll be connecting your multimeter to the TP sensor connector's middle wire and then manually opening and closing the throttle to see if the TP sensor produces a varying DC voltage signal.
    2. TEST 1: Testing the TPS Voltage Signal.
  2. Verify that the TP sensor is getting power (if TEST 1 is failed).
    1. This is a simple multimeter test too.
    2. TEST 2: Verifying TPS Has Power.
  3. Verify that the TP sensor is getting ground (if TEST 1 is failed).
    1. This is a simple multimeter test too.
    2. TEST 3: Verifying TPS Has Ground.

TPS TEST 1: Testing the TPS Voltage Signal


The middle wire (labeled with the number 2 in the illustration) is the one that carries the voltage signal, that the TP sensor creates, back to the PCM.
Using a multimeter, we're gonna' tap into this wire and see if the TP sensor can create and report a variable voltage signal.
Once we're tapped into this circuit, we'll manually rotate the throttle to its opened and closed positions and see if our multimeter now records the TP signal voltage increasing and decreasing.
I'll explain everything in a step-by-step manner in the following instructions.
NOTE: To ensure the accuracy of your test, it's best to test the throttle position sensor (TPS) with the engine warmed up.
OK, let’s start:
Part 1
  1. 1
    Place your multimeter in Volts DC mode and with the RED multimeter lead probe the wire labeled with the number 2 in the photos. This is the circuit that supplies the TP Signal to the PCM.

    If you don't have a multimeter or need to upgrade yours, check out my recommendation: Abe's Multimeter Recommendation (found at: easyautodiagnostics.com).

    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.)
  2. 2
    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).
  3. 3
    Your multimeter should report .4 to .9 Volts DC. If your multimeter doesn't, don’t worry about it just yet, continue with the other steps.
Part 2
  1. 4
    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.
  2. 5
    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 4.9 Volts DC.
  3. 6
    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.
Part 3
  1. 7
    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.
  2. 8
    Repeat step 7 several times to make sure of your multimeter test results.
Let's take a look at your test results:
CASE 1: Multimeter registered a smooth increase or decrease in voltage with no gaps, this is the correct and expected test result. In other words, the TP sensor passed with flying colors.
This test result also let's you know that the problem causing the P1121 trouble code is intermittent and not present at this point in time.
CASE 2: Multimeter DID NOT register a smooth increase or decrease in voltage, and you saw the voltage reading skip or go dead when tapping the TPS... then this means that the throttle position sensor (TPS) is BAD. Replace the throttle position sensor.

CASE 3: Multimeter DID NOT register any voltage, this test result doesn't condemn the TPS as BAD just yet. Why? Because...
... the TPS may be missing either power or ground. So the next step is to check that the TPS is getting power, go to TPS TEST 2: Verifying TPS Has Power.


TPS TEST 2: Verifying TPS Has Power

The wire (circuit) labeled with the number 3 in the illustration is the one that feeds the TP sensor with power.
As stated earlier, this power is in the form of 5 Volts DC and is feed to the TP sensor by the PCM.
If your TP sensor did not show a variable voltage when you manually actuated the throttle in TPS TEST 1, then there's a good chance it's not being fed with power.
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 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 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 (although 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


So far (if you've started from TEST 1), you've confirmed that the TP sensor isn't creating a variable signal, that it's getting power...
... now, we're gonna' check to see if it's getting ground.
This ground is provided by the wire labeled with the number 1, in the illustration in the image viewer.
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 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 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).

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