A trouble code P0122: Throttle Position Sensor Circuit Low Voltage let's you know that your Honda Civic's fuel injection computer has noticed a problem with the voltage signal that the throttle position sensor is sending it.
In this tutorial I'll explain what it means and what's involved in diagnosing and repairing its cause.
I'm also going to show you where to find the test tutorial you'll need to test the throttle position sensor.
Contents of this tutorial:
APPLIES TO: This wiring diagram applies to the following vehicles:
- 1.6L Honda Civic CX: 1996, 1997, 1998, 1999, 2000.
- 1.6L Honda Civic DX: 1996, 1997, 1998, 1999, 2000.
- 1.6L Honda Civic EX: 1996, 1997, 1998, 1999, 2000.
- 1.6L Honda Civic HX: 1996, 1997, 1998, 1999, 2000.
- 1.6L Honda Civic LX: 1996, 1997, 1998, 1999, 2000.
- 1.6L Honda Civic Si: 1999, 2000.
- 1.6L Honda Civic Del Sol S: 1996, 1997.
- 1.6L Honda Civic Del Sol Si: 1996, 1997.
- 1.6L Honda Civic Del Sol VTEC: 1996, 1997.
RELATED TROUBLE CODES:
What Does Trouble Code P0122 Mean?
To understand what a trouble code P0122 means, it's important to know that 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 a malfunction with the throttle position sensor (or its signal circuit) occurs and the TPS signal voltage stays stuck at a low voltage value, 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 1.6L Honda Civic's fuel injection computer relies on the throttle position sensor to know when you've stepped on or off the accelerator pedal.
This makes the throttle position sensor a critical component of the engine management system.
When the TPS 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?
In a nutshell, when you step on the accelerator pedal, the throttle plate opens and more air enters the engine.
When you let off the accelerator pedal, the throttle plate closes and less air enters the engine.
The component that reports the throttle plate's angle (as it opens/closes) to the fuel injection computer is the throttle position sensor.
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:
- 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
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:
- 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 Honda Civic. You can find it here: How To Test The Throttle Position Sensor (Honda 1.6L).
Where To Buy The TP Sensor And Save
The Honda service manual tells you to replace the entire throttle body when the TP sensor fails but you can actually buy it separately.
Where can you buy the TP sensor? You can buy it at your local auto parts store but it's gonna' cost a whole lot more. Check out the following links and compare:
Not sure the TP sensor listed fits your particular Honda? Don't worry, they'll make sure it fits your Honda, once you get to the TP sensor site, or they'll find the right one for you.
More 1.6L Honda Civic Tutorials
You can find a complete list of 1.6L Honda Civic 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 (Honda 1.6L).
- How To Test The Alternator (1996-2000 1.6L Honda Civic).
- Testing Shift Control Solenoid Valves A and B (1996-2000 1.6L Honda Civic).
- How To Troubleshoot A No Start (Honda 1.6L).
- How To Test The Igniter, Ignition Coil Accord, Civic, CRV, and Odyssey (at: easyautodiagnostics.com).
If this info saved the day, buy me a beer!