The P0123: Throttle Position Sensor Circuit High Voltage trouble code is one of the 3 trouble codes that the fuel injection computer will register when there's a problem with the throttle position sensor (TPS) on your 1999-2002 V8 Chevrolet Silverado or GMC Sierra.
You can usually conclude that the throttle position sensor has failed when this trouble code is registered in the computer's memory.
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 P0123 ¿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).
- P0122 -What Does It Mean? (1999-2002 V8 Silverado, Sierra, Suburban, Tahoe, Yukon).
What Does Trouble Code P0123 Mean?
When the throttle position sensor reports a higher than expected throttle plate angle that does not correspond to actual engine RPM, a trouble code P0123: Throttle Position Sensor Circuit High Voltage is registered by the computer.
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 lower than what the sensor is reporting, it then sets a P0123 trouble code.
Common Symptoms Of A P0123 Trouble Code
The fuel injection computer, on your Chevrolet Silverado (GMC Sierra), uses the information of several input sensors for fuel injection calculations.
The throttle position sensor is one of such input engine management sensors that the computer relies on.
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 probably already know, the accelerator pedal is connected to the throttle plate (on the throttle body) via an accelerator cable.
As you step on the accelerator pedal, the throttle plate opens and allows more air into the engine (which increases engine RPM).
As you step off the accelerator pedal, the throttle plate closes and less air is admitted into the engine (which causes engine RPM to decrease).
It's the throttle position sensor's job is to inform the fuel injection computer the throttle plate's angle as it opens/closes.
With this throttle angle information, the computer can now increase/decrease the amount of fuel being injected into the engine.
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 P0123 Trouble Code?
Quite a few thing can cause a P0123 trouble code but generally a bad throttle position sensor is its cause.
Besides a bad TPS, these other conditions can cause a P0123 trouble code:
- The TPS signal wire has a short-circuit problem to the wire that feeds the TPS with 5 Volts.
- The TPS Ground wire has an open-circuit problem between the TPS connector and the fuel injection computer's connector.
- Bad fuel injection computer (although very rare).
How To Diagnose And Repair A P0123 Trouble Code
To diagnose and repair the cause of a P0123 trouble code, you'll need to test the throttle position sensor (with the MAP sensor disconnected from its electrical connector).
The test will check that 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 Chevrolet 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).
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