P0123 -What Does It Mean? (1995-1999 3.8L V6 Buick, Chevrolet, Pontiac, Olds)

A trouble code P0123: Throttle Position Sensor Circuit High Voltage is a very common trouble code that is generally caused by a bad throttle position sensor (TPS).

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.

En Español You can find this tutorial in Spanish here: Código P0123 ¿Qué Significa? (1996-1999 3.8L V6 Buick, Chevrolet, Pontiac, Olds) (at: autotecnico-online.com).

APPLIES TO: This tutorial, on the P0123 OBD II trouble code, applies to the following vehicles:

  1. 3.8L Buick LeSabre: 1996, 1997, 1998, 1999.
  2. 3.8L Buick Park Avenue: 1996, 1997, 1998, 1999.
  3. 3.8L Buick Regal: 1996, 1997, 1998, 1999.
  4. 3.8L Buick Riviera: 1996, 1997, 1998, 1999.

  1. 3.8L Chevrolet Lumina: 1998, 1999.
  2. 3.8L Chevrolet Monte Carlo: 1998, 1999.

  1. 3.8L Oldsmobile 88 (Eighty-Eight): 1996, 1997, 1998, 1999
  2. 3.8L Oldsmobile 98 (Ninety-Eight): 1996
  3. 3.8L Oldsmobile Intrigue: 1998, 1999
  4. 3.8L Oldsmobile LSS: 1996, 1997, 1998, 1999
  5. 3.8L Oldsmobile Regency: 1997, 1998

  1. 3.8L Pontiac Bonneville: 1996, 1997, 1998, 1999
  2. 3.8L Pontiac Grand Prix: 1997, 1998, 1999

What Does Trouble Code P0123 Mean?

A diagnostic trouble code P0123: Throttle Position Sensor Circuit High Voltage lets you know that the throttle position sensor's signal is stuck at a voltage greater than 4.7 Volts for more than one second.

To better understand why this is a problem, take a look at the section: What Does The Throttle Position Sensor Do?

Common Symptoms Of A P0123 Trouble Code

The TPS is a mission-critical component of the engine management system that is used by the fuel injection computer to calculate how much fuel to inject into the engine.

So when it fails, your vehicle's engine performance will suffer. You'll see one or more of the following symptoms:

  1. Rough or low idle.
  2. Very high idle.
  3. Engine may start and stall.
  4. Little to no acceleration

What Does The Throttle Position Sensor Do?

The throttle position sensor's job is to inform the fuel injection computer the throttle plate's angle as it opens/closes.

And as you're probably aware, the throttle plate opens/closes as you step on/off the accelerator pedal (they are connected via the accelerator cable).

When the throttle plate in its closed position (like when the engine is at idle and your foot is off the accelerator pedal), the signal voltage it produces 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?

The most common cause of a P0123 trouble code is a bad throttle position sensor.

Unfortunately, a bad TPS is not the only thing that can cause a P0123 trouble code. The most common are:

  1. The TPS signal wire has a short-circuit problem to the wire that feeds the TPS with 5 Volts.
  2. The TPS Ground wire has an open-circuit problem between the TPS connector and the fuel injection computer's connector.
  3. Bad fuel injection computer (although very rare).

How To Diagnose And Repair A P0123 Trouble Code

Troubleshooting and resolving a P0123 involves testing the throttle position sensor.

This means testing the TPS signal voltage to see if it is truly stuck at a high voltage value as you open/close the throttle plate.

It also means confirming that 5 Volts and Ground are reaching the TPS. You'll need to also make sure that the TPS connector is not damaged and that its 3 wires are not shorted together.

You can conclude that the TPS is bad and needs to be replaced if your test results confirm that:

  1. The TPS signal voltage DOES NOT increase/decrease as you open/close the throttle plate.
  2. The sensor is getting 5 Volts and Ground.
  3. The connector's 3 wires are OK.

You can find the TPS test explained in detail here: How To Test The GM 3.8L Throttle Position Sensor (TPS).

Where To Buy The TPS And Save

The following links will help you comparison shop for the throttle position sensor:

More 3.8L V6 GM Tutorials

You can find a complete list of 3.8L GM V6 tutorials in this index:

  1. GM 3.8L Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

  1. How To Test The MAF Sensor (GM 3.8L V6 1996-2005).
  2. How To Test A Does Not Crank Condition -Case Study (GM 3.8L).
  3. GM 3.8L Ignition Control Module And Crank (3X, 18X) Sensor Test.
  4. How To Test The Ignition Coil Pack -Misfire Troubleshooting Tests (GM 3.8L).
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