P0123 -What Does It Mean? (1996-1998 1.5L Mazda Protege)

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

I'm also going to show you where to find the test tutorial you'll need to test the throttle position sensor and find out if it's good or bad.

You can find this tutorial in Spanish here: P0123 ¿Qué Significa? (1996-1998 1.5L Mazda Protege) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 1.5L Mazda Protege: 1996, 1997, 1998.

RELATED TROUBLE CODES:

• P0122 -What Does It Mean? (1996-1998 1.5L Mazda Protege).

What Does Trouble Code P0123 Mean?

As you're driving down the road, and you're stepping on and stepping off the accelerator pedal, the throttle plate (in the throttle body) opens and closes.

It's the job of the throttle position sensor to monitor the throttle plate as it opens and closes and to report that to the fuel injection computer.

In a good and functioning TPS:

• The throttle position sensor voltage signal increases as the throttle plate opens.
• The throttle position sensor voltage signal decreases as the throttle plate closes.

A trouble code P0123: Throttle Position Sensor Circuit High Voltage will set when:

• The throttle position sensor malfunctions and its TPS signal voltage stays stuck at a high voltage value.
• A problem occurs in the throttle position sensor's wiring and its TPS signal voltage stays stuck at a high value.

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 fuel injection computer relies on the throttle position sensor to know when you've stepped on or off the accelerator pedal, when the TPS 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 briefly mentioned earlier, the TPS is the component that reports the throttle plate's angle (as it opens/closes) to your 1.5L Mazda Protege's fuel injection computer.

Specifically, when you step on the accelerator pedal:

• The throttle plate opens.
• More air enters the engine.
• The computer injects more fuel.
• The engine accelerates.

When you step off the accelerator pedal:

• The throttle plate closes.
• Less air enters the engine.
• The computer injects less fuel.
• The engine decelerates.

What's important to know and remember is that 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 leading cause of a P0123 trouble code is a bad throttle position sensor.

But a P0123 trouble code can be caused by a few other problems (besides a bad TPS). For example:

• 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

To troubleshoot and repair a P0123 trouble code you'll need to test the throttle position sensor. The cool thing is that you can accomplish this test with a simple multimeter.

The throttle position sensor test involves checking that:

• 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.

If the TPS is bad and the cause of the P0123 trouble code, your test results will confirm that:

• The TPS signal voltage DOES NOT increase as you open/close the throttle plate.
• The TPS is receiving 5 Volts.
• The TPS is receiving Ground.

This is the tutorial that'll help you test the TPS on your 1996-1998 1.5L Mazda Protege:

• How To Test The TPS (1995-1998 1.5L Mazda Protege).

Where To Buy The TP Sensor And Save

The following link will help you to comparison shop for the throttle position sensor on your 1.5L Mazda Protege:

Not sure the TP sensor listed fits your particular 1.5L Mazda Protege? Don't worry, they'll make sure it fits your Protege, once you get to the TP sensor site, or they'll find the right one for you.

More 1.5L Mazda Protege Diagnostic Tutorials

You can find a complete list of 1.5L Mazda Protege diagnostic tutorials and wiring diagrams in this index:

• Mazda 1.5L Index Of Articles.

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

• Ignition System Wiring Diagram (1995 1.5L Mazda Protege).
• How To Test The Ignition System (1996-1998 1.5L Mazda Protege).
• How To Test Engine Compression (1995-1998 1.5L Mazda Protege).
• How To Test The MAF Sensor (1996-1998 1.5L Mazda Protege).