P0123 Honda 1.7L – How To Test Civic TPS

When the scan tool for your Honda Civic is showing a stored P0123 Honda trouble code, it means there’s a problem with the throttle position sensor or TPS in your 1.7 liter Honda. This sensor is primarily responsible for reading the angle of your throttle blade, and transmits this positioning to your Honda ECU so that the right amount of fuel and spark can be delivered.

The specific wording behind the P0123 Honda code is Throttle Position Sensor/Switch Circuit High Input. This means that your D17 Honda throttle position sensor is transmitting a signal that your Honda ECU cannot understand. Because this signal is not recognized and is too high for your ECU to use, your 1.7 liter Honda engine may run poorly. Some of the symptoms of this common issue are :

  • Inconsistent throttle response
  • Poor fuel economy
  • Bucking or lurching
  • No response from gas pedal

In order to correct this issue, I will be showing you how to test the signal wire from your Honda Civic throttle position sensor in a 2001 Honda Civic LX with a 1.7 liter engine in it. Because of the nature regarding the P0123 Honda trouble code, I will show you how to test the signal wire using a multi meter to determine what signal your Honda TPS is transmitting.


Common Causes of P0123 trouble code


There are several common problems that can trigger the P0123 check engine light, and this handy guide will help you locate where the problem really lies. Some of the things that can cause your yellow check engine indicator to go on are :

  • Failing Throttle position sensor
  • Problem with wiring
  • TPS error
  • Bad TPS ground

In typical Honda tradition, replacing your Honda throttle body is the only way to change your throttle position sensor if you take your car to a dealership. With the right tools and know-how you can use a throttle position sensor replacement, which is much cheaper than the entire throttle body assembly.

The only issue with this is that you will need to calibrate your sensor once you’ve installed it to your Civic, so that it understands where wide open throttle ends and where the closed throttle position begins.

The replacement TPS part number is T42005 and this repair part typically comes with a gasket and replacement sensor unit. You may need to cut off the posts to your old TPS, so that you can remove the old part from your throttle body.

Where is my Honda Civic throttle position sensor located?

This 3 pin sensor is mounted opposite of the throttle blade, which is connected to your accelerator pedal through your throttle cable. To find this sensor you must remove the plastic cover to your intake manifold at the top of your engine bay.


In order to test your Honda Civic throttle position sensor, you will be using your multimeter to read the voltage signal being sent to your ECU. Once you have your plastic D17 engine cover taken off, you can put the black lead of your multimeter to the negative post of your battery.


This three wire throttle position sensor must be backpinned for this part of your test. To properly backpin your sensor, bend a paperclip into a L shape and shove one end into the middle wire or PIN 2 of your Honda TPS. This wire is red and black and represents the signal wire for your throttle body.

Once you have this middle wire backpinned, you are ready to test your Honda Civic throttle position sensor. Probe the middle backpinned wire with your multimeter after you insert your ignition key and turn to the “ON” position. Do not turn your Civic engine on but make sure that your ignition is turned so that all your engine sensors are properly powered.

How To Test your Civic TPS


The TPS in your Honda Civic is basically a potentiometer that’s designed to increase voltage as your throttle body opens. The typical range for this sensor is between 0 – 5 volts of operation. With your ignition key inserted and turned to the “ON” position, you should see roughly .50 to .45 voltage at the middle signal wire.

If you have this reading at this pin, have a friend sit inside the car and slowly depress the accelerator pedal. If you are working solo on this project, you can use your other hand to manually deflect the throttle body butterfly to open your throttle blade.

You should see your multimeter showing the voltage slowly rising to match the throttle blade opening. Once you have cranked the throttle open all the way, you should see 4.5 volts at this middle wire. Repeat this and make sure that your voltage is climbing evenly and not peaking or missing sections of voltage range. This may result in an intermittent error, which could drive you crazy when trying to track down your TPS voltage issue.

The P0123 Honda trouble code is telling you that the voltage sent is too high, so the next order of business is to slowly close the throttle body. Again you are looking for a smooth transition as you or your friend closes the throttle body.

What happens if my test comes back good but my P0123 Honda code keeps coming back?


If your voltage looks good but your check engine light remains, you may have an intermittent issue with your throttle position sensor. While testing for voltage at wide open throttle or (WOT,) gently tap the side of your sensor to see if the voltage signal disappears during any part of the procedure.

Voltage dips or missing chunks of voltage range can also lead to this trouble code, and when you are tapping the TPS this error can be noticed more easily. Congratulations you now know how to test your TPS to resolve the P0123 Honda check engine code! Have any questions about this guide? Leave us a comment below and let us know!

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