One of the most common throttle position sensor trouble codes is the P0122: Throttle Position Sensor Circuit Low Voltage trouble code.
When this bad boy pops up, you can usually conclude that the throttle position sensor has failed.
In this tutorial, I'll explain what this trouble code means. I'll also talk about some of the tests you can perform to find its cause and solution.
Contents of this tutorial:
You can find this tutorial in Spanish here: Código P0122 ¿Qué Significa? (1999-2002 V8 Silverado, Sierra, Suburban, Tahoe, Yukon) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
Chevrolet:
- Silverado (1500, 2500):
- 4.8L, 5.3L: 1999, 2000, 2001, 2002
- Silverado (2500):
- 6.0L: 1999, 2000, 2001, 2002
- Suburban (1500):
- 5.3L: 2000, 2001, 2002
- Suburban (2500):
- 6.0L: 2000, 2001, 2002
- Tahoe:
- 4.8L, 5.3L: 2000, 2001, 2002
GMC:
- Sierra (1500, 2500):
- 4.8L, 5.3L: 1999, 2000, 2001, 2002
- Sierra (2500):
- 6.0L: 1999, 2000, 2001, 2002
- Yukon:
- 4.8L, 5.3L: 2000, 2001, 2002
- Yukon XL (1500):
- 5.3L: 2000, 2001, 2002
- Yukon XL (2500):
- 6.0L: 2000, 2001, 2002
RELATED TROUBLE CODES:
- P0121 -What Does It Mean? (1999-2002 V8 Silverado, Sierra, Suburban, Tahoe, Yukon).
- P0123 -What Does It Mean? (1999-2002 V8 Silverado, Sierra, Suburban, Tahoe, Yukon).
What Does Trouble Code P0122 Mean?
A trouble code P0122: Throttle Position Sensor Circuit Low Voltage is set when the TPS reports a very low throttle plate angle that does not correspond to actual engine RPM.
The fuel injection computer can predict, based on engine RPM and other inputs, what the TPS voltage signal should be.
When the computer sees that the TPS voltage signal should be higher, when it isn't, it sets a P0122 trouble code.
Common Symptoms Of A P0122 Trouble Code
The throttle position sensor is one of several key input engine management sensors the fuel injection computer uses for fuel injection calculations.
Since the TPS is a critical component 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 is illuminated.
- Rough or low idle.
- Very high idle.
- Engine may start and stall.
- Little to no acceleration
What Does The Throttle Position Sensor Do?
As you're already aware, the accelerator pedal is connected to the throttle plate via an accelerator cable.
As you step on or off the accelerator pedal, the throttle plate opens or closes to admit more less air into the engine.
It's the throttle position sensor's job is to inform the fuel injection computer the throttle plate's angle as it opens/closes.
When the throttle plate is in its closed position (like when the engine is idling and your foot is 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?
A bad throttle position sensor is generally the cause of a P0122 trouble code, but not always.
I've also seen a bad MAP sensor cause this trouble code (since both the MAP and TPS share the same 5 Volt DC power circuit).
Other things that can cause a P0122 trouble code are:
- An open-circuit or short-circuit problem in the TPS signal wire between the TPS and the fuel injection computer.
- A bad TPS connector.
- A bad MAP sensor.
- Throttle position sensor receiving less than 5 Volts from its 5 Volt reference wire.
- Bad fuel injection computer (although very rare).
How To Diagnose And Repair A P0122 Trouble Code
Diagnosing and repairing the cause of a P0122 trouble code involves testing the throttle position sensor with the MAP sensor disconnected from its electrical connector.
The purpose of the throttle position sensor test is to see if the TPS signal voltage increases/decreases as you manually open/close the throttle plate.
The test also includes making sure that the throttle position sensor is getting 5 Volts and Ground from the fuel injection computer.
If the TPS signal voltage DOES NOT increase as you open/close the throttle plate and the sensor is getting 5 Volts and Ground, then you can conclude that the sensor is bad and needs to be replaced.
If the TPS is good, then the next step is to test the MAP sensor.
You can find the TPS test explained in detail here: How To Test The TPS (1999-2002 V8 Chevrolet Silverado, GMC Sierra).
Where To Buy The TPS And Save
The following links will help you comparison shop for the throttle position sensor. The AC-Delco brand is the original equipment brand for all Chevrolet and GMC vehicles:
More Silverado, Sierra, Suburban, Tahoe, And Yukon Tutorials
You can find a complete list of V8 Silverado, Sierra, Suburban, Tahoe, and Yukon tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- Resistance Specifications Of The TAC Electronic Throttle Body.
- How To Test The GM Accelerator Pedal Position (APP) Sensor 2.
- How To Test The MAF Sensor (GM 4.8L, 5.3L, 6.0L, 8.1L).
- Blown Head Gasket Test (GM 4.8L, 5.3L, 6.0L).
If this info saved the day, buy me a beer!
