2009 chevy cobalt has p0641 code with traction control turned off, engine in reduced power mode

have the fault codes read and fix the fault that put the ECM in limp mode
reset the ECM on completion of repairs

You'll need someone to check the engine computer for trouble codes with a scanner or code reader.
The codes will tell you or a mechanic what to test.

2010 Chevy Cobalt code P0641 Yahoo Answers

Possible causes
- Faulty Engine Control Module (ECM)
- ECM harness is open or shorted
- ECM circuit poor electrical connection
- Shorted sensor on 5 volt circuit
What does this mean? When is the code detected?
The Engine Control Module (ECM) has detected the sensor 5 volt reference circuit voltage is higher or lower than expected
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
P0641 Chevrolet Description
The control module has 2 internal 5-volt reference buses called "5-volt reference 1" and"5-volt reference 2". Each reference bus provided 5-volt reference circuit for more than one sensor. Therefore, a fault condition on one 5-volt reference circuit will affect the other 5-volt reference circuits connected to the reference bus. The control module monitors the voltage on the 5-volt reference buses.

Read more: http://engine-codes.com/p0641_chevrolet.html#ixzz31AP60YfR

go to www.automecanico.com + www.autoelectronico.com translate the website amazing with your browser and fix it.
God bless you

As far as the cobalt, check tac/throttle actuator control. Below is circuit description for p1682.
The other codes was for knock sensor.

The check engine light being on now is a different problem , Have DTC'S - diagnostic trouble codes checked ,will have something to do with electronic throttle control . That is what reduced engine power is about . It's in a reduced power mode.
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.

Do you know what electronic throttle control is ?
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Throttle Actuator Control (TAC) System Description

The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and eliminates the need for mechanical cable. The TAC system performs the following functions:
• Accelerator pedal position sensing
• Throttle positioning to meet driver and engine demands
• Throttle position sensing
• Internal diagnostics
• Cruise control functions
• Manage TAC electrical power consumption
The TAC system includes the following components:
• The accelerator pedal position (APP) sensors
• The throttle body assembly
• The engine control module (ECM)

Your best bet , take it to a qualified repair shop .

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

That is a hard problem to pin point without knowing what codes the computer has stored. It can be any number or sensors or engine problems.

You can go to most auto parts stores and they will pull the codes for you for free.