P0641 engine power reduced

Tiny
KLK023
  • MEMBER
  • 2007 CHEVROLET COBALT
Engine Mechanical problem Automatic 63,300 miles

while driving after 20 minutes the check engine light will come on and it will read engine power reduced at which time you can't go over 40 miles an hour, so I pulled over and waited a minute and restarted it and it runs fine and happens again 10 or 15 min later. Today I tried to drive through it and it ran fine for about two minutes then said engine disabled, pulled over waited a few minutes and restarted, ran fine. Took it to napa auto parts so they could run the code and it was p0641. Let it idle for 20 min and it said engine disabled again so they unplugged the mass intake sensor and decided that it was working. The chevy house said they couldn't get it to do the engine reduced power. Any suggestions
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Saturday, September 11th, 2010 AT 4:32 PM

16 Replies

Tiny
KEN
  • ADMIN
Hello,

This code has to do with the 5 volt reference the computer uses to run the system. This is typical of the computer going bad and needed replacement.

Please let us know what happens.

Cheers, Ken
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Thursday, July 13th, 2017 AT 6:25 PM
Tiny
DARLAJAMES
  • MEMBER
  • 2007 CHEVROLET COBALT
  • 17,100 MILES
Yesterday I was driving in the rain and my low fuel light came on, normally my gas gage is lower before the light would come on, so I exited to go to the station and the dash said engine power reduced and I could do nothing but coast and when I would try to start it it would die right after
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Thursday, July 13th, 2017 AT 6:26 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • EXPERT
You need to have the computer scanned to identify where the problem is coming from. Most parts stores will do it for free or lend you a scanner.
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Thursday, July 13th, 2017 AT 6:26 PM (Merged)
Tiny
MECHANICALIDIOT
  • MEMBER
Im have a similar problem with my 05 cobalt im getting P0340
P0601 as the codes any ideas on how to fix it
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Thursday, February 1st, 2018 AT 5:26 PM
Tiny
KEN
  • ADMIN
Hello,

This will be a camshaft angle sensor that is not working right. Here is a guide to help you see what you are in for when doing the job.

https://www.2carpros.com/articles/camshaft-angle-sensor-replacement

Here is where is is in your car

Check out the diagrams (Below)

Let us know what happens and please upload pictures or videos of the problem.

Cheers, Ken
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Friday, February 2nd, 2018 AT 11:33 AM
Tiny
MECHANICALIDIOT
  • MEMBER
Its that easy to fix it! I took it to a firestone and they told my like 6 things need to do to fix it along with changing out the pcm. Im super happy its that simple, thank you.
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Friday, February 2nd, 2018 AT 12:34 PM
Tiny
MECHANICALIDIOT
  • MEMBER
Ken I was told that codes could also be bad wires running to the ECM or a low voltage on it would you still recommend changing the angle sensors
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Sunday, February 4th, 2018 AT 6:13 AM
Tiny
KEN
  • ADMIN
Yes I would change the sensors first because they have a high rate of failure if that doesn't work then we can start chasing wiring issues.
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Sunday, February 4th, 2018 AT 11:42 AM
Tiny
MECHANICALIDIOT
  • MEMBER
Im in the engine compartment of my car and im not seeing the sensor anywhere
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Wednesday, February 7th, 2018 AT 12:05 PM
Tiny
MECHANICALIDIOT
  • MEMBER
Just change the sensor and the problem still is happening
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Wednesday, February 7th, 2018 AT 12:30 PM
Tiny
MECHANICALIDIOT
  • MEMBER
Im still getting P0340 intake camshaft position cmp sensor circuit and
P0601 control module read error
We tested the voltage output is at 15.2 VDC
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Wednesday, February 7th, 2018 AT 12:42 PM
Tiny
ASEMASTER6371
  • EXPERT
The 641 code is related to the other code as well. It has to do with a 5 volt reference voltage to the accelerator position sensor, which is the gas pedal.

You need to check the voltage at the sensor and see if you have this 5 volt signal at that sensor as well as the crank sensor as well.

Roy

Circuit/System Description

The engine control module (ECM) has 2 internal 5-volt reference busses called 5-volt reference 1 and 5-volt reference 2. Each reference bus provides 5-volt reference circuits 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 that reference bus. The ECM monitors the voltage on the 5-volt reference busses.

The 5-volt reference 1 bus provides 5 volts to the following sensors:

* The manifold absolute pressure (MAP) sensor
* The fuel tank pressure (FTP) sensor
* The air conditioning (A/C) refrigerant pressure sensor
* The accelerator pedal position (APP) sensor 2
* The intake camshaft position (CMP) sensor

The 5-volt reference 2 bus provides 5 volts to the following sensors:

* The APP sensor 1
* The throttle position (TP) sensor 1 and 2
* The crankshaft position (CKP) sensor

Conditions for Running the DTC

* DTCs P0601, P0602, P0603, P0604, P0605, P0606, P0607, and P2610 are not set.
* The ignition is in Unlock, Accessory, Run, or Crank.
* The ignition voltage is more than 5.23 volts.
* DTCs P0641 and P0651 run continuously when the above conditions are met.

Conditions for Setting the DTC

The ECM detects a voltage out of tolerance condition on the 5-volt reference 1 or 2 bus for more than 0.5 second.

Action Taken When the DTC Sets

DTCs P0641 and P0651 are Type A DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0641 and P0651 are Type A DTCs.

Diagnostic Aids

It may be possible to locate the fault by disconnecting one component at a time from the 5-volt reference circuit while viewing the 5-Volt Reference circuit parameter on the scan tool. The scan tool parameter would change from Fault to OK when the source of the fault is disconnected.

If all 5-volt reference components have been disconnected and a Fault is still indicated, the fault may exist in the wiring harness.

Circuit/System Verification

With the ignition ON and the engine OFF, observe the 5-volt Reference 1 and 2 parameters. The scan tool should display 4.3-4.7 volts for a normally operating system.

Circuit/System Testing

Important: Additional DTCs will set when disconnecting the components.

1. Ignition OFF, disconnect the harness connector of all appropriate sensors for the applicable DTC.

Important: A short to voltage on the signal circuit of certain components may cause this DTC to set.

2. Ignition ON, measure for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.

If the voltage is less than the specified value, test for a short to ground on all the 5-volt reference circuits. If all circuits test normal, replace the control module.
If the voltage is greater than the specified value, test for a short to voltage on all the 5-volt reference circuits, or the signal circuit, for each component associated with the appropriate 5-volt reference circuit. If all circuits test normal, replace the control module.

3. Connect each component associated with the 5-volt reference circuit, one at a time, while monitoring the voltage. The voltage should not change more than 1 volt.

If the voltage display changes more than the specified value when a component is connected, replace the component.

Repair Instructions

* Accelerator Pedal Position Sensor Replacement
* Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
* Control Module References for ECM replacement, setup, and programming
* Fuel Tank Pressure Sensor Replacement
* Manifold Absolute Pressure Sensor Replacement
* Throttle Body Assembly Replacement
* Camshaft Position Sensor Replacement - Intake
* Crankshaft Position Sensor Replacement

Repair Verification

With the ignition ON and the engine OFF, observe the 5-Volt Reference 1 and 2 parameters. The scan tool should display 4.3-4.7 volts for a normally operating system.
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Thursday, February 8th, 2018 AT 1:53 AM
Tiny
MECHANICALIDIOT
  • MEMBER
So if I do all of that I should be able to figure out what is wrong with my car
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Thursday, February 8th, 2018 AT 10:58 AM
Tiny
ASEMASTER6371
  • EXPERT
Did you check any of the tests on the flow chart?

Roy
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Thursday, February 8th, 2018 AT 12:08 PM
Tiny
MECHANICALIDIOT
  • MEMBER
No yet my buddy is the one with the tools I was checking to see if that chart would go to the codes I had
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Thursday, February 8th, 2018 AT 12:30 PM
Tiny
ASEMASTER6371
  • EXPERT
Yes, it is related to both codes

Roy
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Thursday, February 8th, 2018 AT 12:35 PM

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