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.
Contents of this tutorial:
You can find this tutorial in Spanish here: Código P0122 ¿Qué Significa? (1996-2002 2.0L Mazda 626) (at: autotecnico-online.com).
APPLIES TO: This tutorial, on the P0122 OBD II trouble code, applies to the following vehicles:
- 2.0L Mazda 626: 1996, 1997, 1998, 1999, 2000, 2001, 2002.
RELATED TROUBLE CODES:
- P0121 -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 P0122 Mean?
The throttle position sensor (TPS) 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
Your Mazda 626's fuel injection computer relies on the throttle position sensor to calculate how much fuel to inject into the engine, since it alerts it to changes in the throttle plate angle.
Since the TPS is an important part of the engine management system, when it 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?
The throttle position sensor's job is to report the changes in the throttle plate's angle as it opens/closes.
And as you're probably aware, the accelerator pedal is connected to the throttle plate via an accelerator cable. So when you step on/off the accelerator pedal, the throttle plate opens/closes.
As you step on the accelerator pedal, the throttle plate opens and more air rushes into the engine. With more air entering the engine, the fuel injection computer needs to inject more fuel.
As you step off the accelerator pedal, less air enters the engine. With less air entering the engine, the fuel injection computer needs to inject less fuel.
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/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. 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.
- 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
Troubleshooting and repairing a P0122 trouble code involves testing the throttle position sensor and making sure that:
- 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 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.
I've written a tutorial that'll help you test the TPS on your 1996-2002 2.0L Mazda 626. You can find it here: 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 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:
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).
If this info saved the day, buy me a beer!