P0122 -What Does It Mean? (1996, 1997, 1998, 1999, 2000 1.8L Mazda Protege)

In this tutorial I'll explain what a trouble code P0122: Throttle Position Sensor Circuit Low Voltage means and what's involved in diagnosing and repairing its cause.

I'm also going to direct you to the TPS test tutorial that you'll need to test the throttle position sensor.

En Español You can find this tutorial in Spanish here: P0122 ¿Qué Significa? (1996-2000 1.8L Mazda Protege) (at: autotecnico-online.com).

APPLIES TO: This tutorial, on the P0122 OBD II trouble code, applies to the following vehicles:

  1. 1.8L Mazda Protege: 1996, 1997, 1998, 1999, 2000.

RELATED TROUBLE CODES:

  1. P0123 -What Does It Mean? (1996-2000 1.8L Mazda Protege).

What Does Trouble Code P0122 Mean?

Your 1.8L Mazda Protege's throttle position sensor produces a voltage signal that corresponds to the throttle plate angle.

Specifically, 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 P0122: Throttle Position Sensor Circuit Low Voltage sets and lights up the check engine light when the TPS signal voltage stays stuck at low voltage 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

The throttle position sensor is one of several input sensors that the fuel injection computer uses to calculate the amount of fuel to inject into the engine.

Since the throttle position sensor is a critical component of the engine management system of your 1.8L Mazda Protege, when it fails 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 accelerator pedal is connected to the throttle plate, on the throttle body, by an accelerator cable.

So, when you step on the accelerator pedal:

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

When you step off the accelerator pedal:

  1. The throttle plate closes.
  2. Less air enters the engine.
  3. The fuel injection computer injects less fuel into the engine.
  4. The engine decelerates.

The engine management component that is tasked with monitoring and reporting the throttle plate angle, as it opens and closes, is the throttle position sensor.

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

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 or 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.

But a bad TPS is not the only issue that can cause a P0122 trouble code. The following problems can also cause this trouble code:

  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 a very rare problem).

How To Diagnose And Repair A P0122 Trouble Code

A trouble code P0122 can easily be diagnosed and repaired by testing the throttle position sensor.

The TPS test involves:

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

Where To Buy The TPS And Save

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

More 1.8L Mazda Protege Tutorials

You can find a complete list of 1.8L Mazda Protege tutorials in this index:

  1. Mazda 1.8L Index Of Articles.

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

  1. How To Test Engine Compression (1995-2000 1.8L Mazda Protegé).
  2. How To Test For a Blown Head Gasket (1995-2000 1.8L Mazda Protegé).
  3. How To Test The Fuel Injectors (1999-2000 1.8L Mazda Protegé).
  4. How To Test The MAF Sensor (1999-2000 1.8L Mazda Protegé).
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