P0123 -What Does It Mean? (1996-2000 1.6L Honda Civic)

In this tutorial I'll explain what a P0123: Throttle Position Sensor Circuit High Voltage means and what's involved in diagnosing and repairing its cause.

I've also included the link to the tutorial you'll need to test your 1.6L Honda Civic's throttle position sensor.

APPLIES TO: This wiring diagram applies to the following vehicles:

• 1.6L Honda Civic CX: 1996, 1997, 1998, 1999, 2000.
• 1.6L Honda Civic DX: 1996, 1997, 1998, 1999, 2000.
• 1.6L Honda Civic EX: 1996, 1997, 1998, 1999, 2000.
• 1.6L Honda Civic HX: 1996, 1997, 1998, 1999, 2000.
• 1.6L Honda Civic LX: 1996, 1997, 1998, 1999, 2000.
• 1.6L Honda Civic Si: 1999, 2000.
• 1.6L Honda Civic Del Sol S: 1996, 1997.
• 1.6L Honda Civic Del Sol Si: 1996, 1997.
• 1.6L Honda Civic Del Sol VTEC: 1996, 1997.

RELATED TROUBLE CODES:

• P0122 -What Does It Mean? (1996-2000 1.6L Honda Civic).

What Does Trouble Code P0123 Mean?

To understand what a trouble code P0123 means, it's important to know that the throttle position sensor (TPS) creates a voltage signal that increases or decreases according to the movement (angle) of the throttle plate.

In a nutshell, as the throttle plate opens, the TPS signal voltage increases. As the throttle plate starts to close, the TPS signal voltage decreases.

A trouble code P0123: Throttle Position Sensor Circuit High Voltage is set by the fuel injection computer when one of the following occurs:

• The TPS signal voltage does not increase/decrease as the throttle plate opens/closes but stays stuck at a high voltage value.
• The TPS signal voltage is higher than the value the fuel injection computer predicts it should be.

For a more detailed explanation of how the TPS works, take a look at the section: What Does The Throttle Position Sensor Do?

Common Symptoms Of A P0123 Trouble Code

Since the TPS is the input sensor the fuel injection computer relies on to know when you've stepped on or off the accelerator pedal, when it fails engine performance will suffer.

You'll see one or more of the following symptoms:

• Check engine light illuminated with a TPS trouble code.
• Rough or low idle.
• Very high idle.
• Engine may start and stall.
• Little to no acceleration

What Does The Throttle Position Sensor Do?

As I've already mentioned before, when you step on the accelerator pedal, the throttle plate opens. This in turn causes more air to enter the engine.

When you let off the accelerator pedal, the throttle plate closes and less air enters the engine.

The component that reports the throttle plate's angle (as it opens/closes) to the fuel injection computer is the throttle position sensor.

At closed throttle position (for example, you've got your foot off the accelerator pedal), the TPS signal voltage is about 0.4 to 0.9 Volts DC.

Now, as the throttle plate opens, the throttle position sensor signal voltage increases. At wide open throttle (WOT), the TPS signal voltage is around 4.5 Volts.

As the throttle plate closes, the throttle position sensor signal voltage decreases.

As long as the fuel injection computer sees the TPS voltage signal increasing/decreasing, it knows you're stepping ON/OFF the accelerator pedal (and that the TPS is functioning correctly).

What Causes A P0123 Trouble Code?

The most common cause of a P0123 trouble code is a bad throttle position sensor.

Unfortunately, a P0123 trouble code can be caused by a few other problems (besides a bad TPS).

These are:

• An open-circuit problem in the TPS signal wire between the TPS and the fuel injection computer.
• An short-circuit problem in the TPS signal wire between the TPS and the fuel injection computer.
• A bad TPS connector.
• Bad fuel injection computer (although a very rare problem).

How To Diagnose And Repair A P0123 Trouble Code

You can easily troubleshoot and repair your 1.6L Honda Civic's P0123: Throttle Position Sensor Circuit High Voltage trouble code by testing the throttle position sensor.

The throttle position sensor test is done with a simple multimeter and it involves:

• The TPS signal voltage increases/decreases as the throttle plate opens/closes (and is not stuck producing a high voltage value).
• The TPS is getting 5 Volts from the fuel injection computer.
• The TPS is getting Ground from the fuel injection computer.

You can correctly conclude that the TPS is bad and the cause of the P0123 trouble code if:

• Your test results confirm that the TPS signal voltage DOES NOT increase as you open/close the throttle plate.
• Your test results confirm that the TPS is getting 5 Volts.
• Your test results confirm that the TPS is getting Ground.

I've written a tutorial that'll help you test the TPS on your 1996-2002 2.0L Honda Civic. You can find it here: How To Test The TPS (1994-2002 2.0L Honda Civic).

Where To Buy The TP Sensor And Save

The Honda service manual tells you to replace the entire throttle body when the TP sensor fails but you can actually buy it separately.

Where can you buy the TP sensor? You can buy it at your local auto parts store but it's gonna' cost a whole lot more. Check out the following links and compare:

Not sure the TP sensor listed fits your particular Honda? Don't worry, they'll make sure it fits your Honda, once you get to the TP sensor site, or they'll find the right one for you.

More 1.6L Honda Civic Tutorials

You can find a complete list of 1.6L Honda Civic tutorials in this index:

• Honda 1.6L Index of Articles.

Here's a small sample of the tutorials you'll find in the index:

• How To Test For A Blown Head Gasket (Honda 1.6L).
• How To Test The Alternator (1996-2000 1.6L Honda Civic).
• Testing Shift Control Solenoid Valves A and B (1996-2000 1.6L Honda Civic).
• How To Troubleshoot A No Start (Honda 1.6L).
• How To Test The Igniter, Ignition Coil Accord, Civic, CRV, and Odyssey (at: easyautodiagnostics.com).