P0123 -What Does It Mean? (1996-2002 2.0L Mazda 626)

In this article I'll explain what a trouble code P0123: Throttle Position Sensor Circuit High Voltage means and what you'll need to do to diagnose and repair its cause.

I've also included a link to the TPS test tutorial that is going to help you test the throttle position sensor and find out if it's bad (or not).

You can find this tutorial in Spanish here: Código P0123 ¿Qué Significa? (1996-2002 2.0L Mazda 626) (at: autotecnico-online.com).

APPLIES TO: This tutorial, on the P0123 OBD II trouble code, applies to the following vehicles:

• 2.0L Mazda 626: 1996, 1997, 1998, 1999, 2000, 2001, 2002.

RELATED TROUBLE CODES:

• P0122 -What Does It Mean? (1996-2002 2.0L Mazda 626).
• P0123 -What Does It Mean? (1996-2002 2.0L Mazda 626).

What Does Trouble Code P0123 Mean?

It's the throttle position sensor's job to measure the throttle plate angle as it opens/closes when you step on/off the accelerator pedal.

To be a bit more specific:

• When you step on the accelerator pedal and the throttle plate opens, the TPS creates a voltage signal that increases.
• As you step off the accelerator pedal and the throttle plate starts to close, the TPS signal voltage decreases.

All of these TPS signal voltage changes are reported directly to your Mazda 626's fuel injection computer.

When the TPS signal voltage stays stuck in a high voltage value, as the throttle plate opens and closes, the fuel injection computer sets a trouble code P0123: Throttle Position Sensor Circuit High Voltage and lights up the check engine light on the instrument cluster.

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

One of the key input sensors the fuel injection computer uses to calculate how much fuel to inject into the engine is the throttle position sensor.

Naturally, when the throttle position sensor fails, your Mazda 626's 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?

The accelerator pedal is connected to the throttle plate via an accelerator cable.

As you step on the accelerator pedal, the throttle plate opens and admits more air into the engine. This requires that the fuel injection computer injects more fuel into the engine.

As you step off the accelerator pedal, less air is admitted into engine. With less air entering the engine, the fuel injection computer needs to inject less fuel.

It's the throttle position sensor's job to constantly monitor the throttle plate angle and report it to the fuel injection computer.

The throttle position sensor does this by producing a signal voltage that increases as the throttle plate opens and decreases as it closes.

To be a bit more specific:

• At closed throttle plate position (for example, you've got your foot off the accelerator pedal), the 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?

A bad throttle position sensor is generally the most common cause of a P0123 trouble code.

Unfortunately, a bad TPS is not the only thing that can cause a P0123 trouble code. Here's a basic list of a few other things that can cause it:

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

How To Diagnose And Repair A P0123 Trouble Code

A trouble code P0123 can easily be diagnosed and repaired by testing the throttle position sensor to see if it's bad (or not).

The throttle position sensor can easily be tested with a multimeter to see if:

• The TPS signal voltage increases/decreases as the throttle plate opens/closes (and is not stuck producing a low 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.

The following tutorial help you test the TPS on your 1996-2002 2.0L Mazda 626: How To Test The TPS (1994-2002 2.0L Mazda 626).

Where To Buy The TPS And Save

The following links will help you comparison shop for the throttle position sensor of a known and solid automotive name brand (Walker Products):

More 2.0L Mazda 626 Tutorials

You can find a complete list of 2.0L Mazda 626 tutorials in this index:

• Mazda 2.0L 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 (2.0L Mazda 626).
• How To Test The MAF Sensor (1996-1997 2.0L Mazda 626).
• How To Test Engine Compression (2.0L Mazda 626).
• How To Test The Fuel Pump (1994-1999 2.0L Mazda 626).