Reduced power light came on

Your best bet would be to take your vehicle to a qualified repair shop that knows how to test an not guess as to the problem . Having control modules checked for DTC's - diagonstic trouble codes should always be the first step diagnosing modern automobiles . Replacing parts is not the way to try an fix your car. Would hate for you to replace a part an not have it fix the vehicle . Engine power reduced is associated with the electronic throttle control , no speed sensor .
ENGINE POWER REDUCED
Throttle Actuator Control (TAC) System Description for 3.6L engine or Throttle Actuator Control (TAC) System Description for the 2.4L engine

The engine control module (ECM) is the control center for the throttle actuator control (TAC) system. The ECM determines the driver's intent based on input form the accelerator pedal position sensors, then calculates the appropriate throttle response based on the throttle position sensors. The ECM achieves throttle positioning by providing a pulse width modulated voltage to the throttle actuator motor. The throttle blade is spring loaded in both directions, and the default position is slightly open.
002 Electronic Throttle Operation
Drive by Wire Function and diagnostics by Wells
Reduced power mode will cause traction control system to be shut off turning on the light . Nothing wrong with traction control.
So do yourself a favor an take it to a GM dealer or someother qualified repair shop .

The throttle actuator opens the throttle. Your gas pedal is really just a switch that sends an electrical signal to the computer which in turn opens the throttle body with an electric servo motor. On most gm products the actuator is a part of the throttle body and cannot be replaced seperately. This is an accurate code and the only way to be sure (without having a dealers repair manual and thousands of dollars of test equipment) is to replace it. I had this same issue with my 04 Cadillac. Bought a used throttle body for 1/3 price of new on ebay and ran fine for several years until I sold it.

2003 Silverado 2500HD REDUCED ENGINE POWER - Discussion on Topix

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Dec 28, 2009 - 20 posts - ‎12 authors I have replaced the throttle body, had the wires re-connected and .... The gauges all went wild and reduced engine power displayed on the dash. I looked it .... The truck just went to idle for no reason and it keeps happening. 2003 Chevy Trailblazer-CHECK ENGINE LIGHT AND ...
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Reduced Engine Power Message Displayed on GM Vehicles

www.underhoodservice.com/tech-tip-reduced-engine-power-message-dis...
Dec 10, 2012 - Tech Tip: Reduced Engine Power Message Displayed on GM Vehicles ... Model year 2008-'10 vehicles must have the engine control module (ECM) reprogrammed ... Do not drop the electronic throttle control components.

Your caddy has Electronic throttle control ,drive by wire ! Do you know what this is ? You gas pedal ,if you look at it has wires connected to it .These wires hook up to the engine computer ,the engine computer has more wires that hook up to a dc electric motor under the hood on the throttle body which open an close the throttle plate ,which makes the vehicle go faster or slow down !

Are there any messages on your dash REDUCED POWER ? Check engine light lit ?

Pt 1 2007 Chevy 2500HD Reduced Engine Power Warning Fault Code P1516...

have seen it last a few days...

I suggest you tell us what this mystery vehicle is so we can try to help. But from what you described i would start by checking fuel pressure at the fuel rail. And changing the fuel filter.

Most of the time with the 5.3L in the GM vehicles it is a problem with the Throttle body for P1235 code. Usually you can pull the air intake off the throttle body, take a rag with some break cleaner and open the plate. Clean the inside of plate and throttle body. I will probably be Black Gunk build up that comes off. Just clean it really well. The sensor between the pedal and the throttle body have match signals. If one is off then it goes into reduced power mode. So this can be caused by this residue build up. It usually will fix your issue. It can come back but it will get you back on the road and help take you out of limp mode or reduced power mode.

These are not codes , they are warning lights , telling you the driver that a problem exist . code says, traction control off,next code says ,service stabilitrak and the last code says...engine power reduced. DTC'S - diagnostic trouble codes could be stored in the control modules that control these system's . The main problem is more then likely with the reduced engine power. This is because of a problem with the electronic throttle control system . This problem will turn off these other thing's , turning on their light's .
Throttle Actuator Control (TAC) System Description
All newer vehicles have this ! There are position sensors in the Gas pedal and on the throttle body on the engine , The computer uses a DC volt electric motor to make the vehicle go . The sensors wear over time , the motor can wear , wiring can break etc...
Reduced Engine Power Mode
When the ECM detects a condition with the TAC system, the ECM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions:
• Acceleration limiting--The ECM will continue to use the accelerator pedal for throttle control; however, the vehicle acceleration is limited.
• Limited throttle mode--The ECM will continue to use the accelerator pedal for throttle control; however, the maximum throttle opening is limited.
• Throttle default mode--The ECM will turn off the throttle actuator motor and the throttle will return to the spring loaded default position.
• Forced idle mode--The ECM will perform the following actions:
- Limit engine speed to idle by positioning the throttle position, or by controlling the fuel and spark if the throttle is turned off.
- Ignore the accelerator pedal input.
• Engine shutdown mode--The ECM will disable fuel and de-energize the throttle actuator.
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I work at a chevy dealer an can not believe the one you took it to can't find the problem . Where is this dealer ? I will have a long talk with my district rep.
Drive by Wire Function and diagnostics by Wells

This has nothing to do with the heat on the vehicle .
Reduced Power
The reduced power telltale is turned ON by the cluster when it receives a command from the body control module (BCM). The engine control module (ECM) (L81) engine sends a message to the BCM over the CAN serial data link.
The reduced power telltale is illuminated when the ECM is limiting engine torque in a low traction situation. This telltale is used only for the V6 (L81) engine application.
The reduced power telltale is turned ON by the cluster for 2-3 seconds, when the ignition is turned to RUN, for a visual system check.

Taking the vehicle to a qualified repair shop an having it diagnosed would be your best . Unless you have a factory tech 2 scan tool to read BCM DTC'S - diagnostic trouble code's an have factory diagnostic repair info.
Reduced Engine Power Mode
When the ECM detects a condition with the TAC system, the ECM may enter a reduced engine power mode. Reduced engine power may cause one or more of the following conditions:
• Acceleration limiting--The ECM will continue to use the accelerator pedal for throttle control; however, the vehicle acceleration is limited.
• Limited throttle mode--The ECM will continue to use the accelerator pedal for throttle control; however, the maximum throttle opening is limited.
• Throttle default mode--The ECM will turn off the throttle actuator motor and the throttle will return to the spring loaded default position.
• Forced idle mode--The ECM will perform the following actions:
• Limit engine speed to idle by positioning the throttle position, or by controlling the fuel and spark if the throttle is turned off.
• Ignore the accelerator pedal input.
• Engine shutdown mode--The ECM will disable fuel and de-energize the throttle actuator.

Yup. The throttle body connectors have a history of failing on these cars. Replace the throttle body and the wire connectors that go to it, and you're back in business. Not terribly difficult and you can get the parts from any dealer. Saturn actually has a bulletin out on this problem but they won't cover it unless you're under warranty - no recall for this.