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.
Contents of this tutorial:
You can find this tutorial in Spanish here: Código P0122 ¿Qué Significa? (1999-2001 1.6L Mazda Protege) (at: autotecnico-online.com).
APPLIES TO: This tutorial, on the P0122 OBD II trouble code, applies to the following vehicles:
- 1.6L Mazda Protege: 1999, 2000, 2001.
RELATED TROUBLE CODES:
What Does Trouble Code P0122 Mean?
The throttle position sensor (TPS), on your 1.6L Mazda Protege, creates a voltage signal that increases as the throttle plate opens.
Once the throttle plate starts to close, the TPS signal voltage decreases.
When the TPS signal voltage stays is stuck at a very low voltage, when it should be greater, a trouble code P0122: Throttle Position Sensor Circuit Low Voltage is set by the fuel injection computer.
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 fuel injection computer, of your 1.6L Mazda Protege, relies on several input sensors to calculate the amount fuel to inject into the engine.
The throttle position sensor is one of such input sensors that are critical to the engine management system of your 1.6L Mazda Protege.
When the throttle position sensor fails, 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?
Since the throttle plate is connected to the accelerator pedal, via an accelerator cable, when you step on or off the accelerator pedal, the throttle plate opens or closes.
As you're probably already aware, when you step on the accelerator pedal, more air enters the engine and it accelerates.
With more air entering the engine, the fuel injection computer has to inject more fuel into it.
When you step off the accelerator pedal, less air enters the engine and it decelerates.
With less air entering the engine, the fuel injection computer now has two inject last fuel into it.
It's the throttle position sensor's job to monitor and report the throttle plate angle, as it opens and closes, to the fuel injection computer.
When the throttle plate is closed (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 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.
Unfortunately, a bad TPS is not the only cause of a P0122 trouble code. The following problems can also cause this trouble code:
- 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.
- The throttle position sensor is not receiving 5 Volts.
- A bad TPS connector.
- Bad fuel injection computer (although very rare).
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:
- Making sure that the TPS signal voltage increases/decreases as the throttle plate opens/closes (and is not stuck producing a low voltage value).
- Making sure that the TPS is getting 5 Volts from the fuel injection computer.
- 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:
- 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.
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 name brand (Walker Products):
More 1.6L Mazda Protege Tutorials
You can find a complete list of 1.6L Mazda Protege tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test For A Blown Head Gasket (1.6L Mazda Protegé).
- How To Test The Fuel Injectors (1999-2001 1.6L Mazda Protegé).
- How To Test Engine Compression (1999-2001 1.6L Mazda Protegé).
- How To Test The Ignition Coils (1999-2001 1.6L Mazda Protegé).
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