P0122 -What Does It Mean? (1996, 1997, 1998 1.5L Mazda Protege)

In this tutorial I'll explain what a P0122: Throttle Position Sensor Circuit Low 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.

En Español You can find this tutorial in Spanish here: P0122 ¿Qué Significa? (1996-1998 1.5L Mazda Protege) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

  1. 1.5L Mazda Protege: 1996, 1997, 1998.

RELATED TROUBLE CODES:

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

What Does Trouble Code P0122 Mean?

In a nutshell, when the engine is running, the throttle position sensor monitors the throttle plate angle as you step on and step off the accelerator pedal.

In a good and functioning TPS, as the throttle plate opens, the throttle position sensor voltage signal increases.

And as the throttle plate closes, the TPS voltage signal decreases.

A throttle position sensor trouble code will set when:

  1. The throttle position sensor malfunctions and its TPS signal voltage stays stuck at a low voltage value.
  2. A problem occurs in the throttle position sensor's wiring and its TPS signal voltage stays stuck at a low 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 P0122 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:

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

What Does The Throttle Position Sensor Do?

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

Specifically, when you step on the accelerator pedal:

  1. The throttle plate opens.
  2. More air enters the engine.
  3. The computer injects more fuel.
  4. The engine accelerates.

When you step off the accelerator pedal:

  1. The throttle plate closes.
  2. Less air enters the engine.
  3. The computer injects less fuel.
  4. 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 P0122 Trouble Code?

The most common cause of a P0122 trouble code is a bad throttle position sensor.

Unfortunately, a P0122 trouble code can be caused by a few other problems (besides a bad TPS). Here's a basic list of a few other things that can cause it:

  1. An open-circuit problem in the TPS signal wire between the TPS and the fuel injection computer.
  2. An short-circuit problem in the TPS signal wire between the TPS and the fuel injection computer.
  3. The throttle position sensor is not receiving 5 Volts.
  4. A bad TPS connector.
  5. Bad fuel injection computer (although very rare).

How To Diagnose And Repair A P0122 Trouble Code

Testing to see if the throttle position sensor is bad (or not) is the way to troubleshoot and repair a P0122 trouble code.

The throttle position sensor test involves:

  1. Verifying that the TPS signal voltage increases/decreases as the throttle plate opens/closes (and is not stuck producing a low voltage value).
  2. Verifying that the TPS is getting 5 Volts from the fuel injection computer.
  3. Verifying that the TPS is getting Ground from the fuel injection computer.

You can correctly conclude that the TPS is bad and the cause of the P0122 trouble code if:

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

I've written a tutorial that'll help you test the TPS on your 1995-1998 1.5L Mazda Protege. You can find it here: How To Test The TPS (1995-1998 1.5L Mazda Protege).

Where To Buy The TP Sensor And Save

The following links 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:

  1. Mazda 1.5L Index Of Articles.

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

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