Code P0641, causing reduced engine power?

Tiny
DSMITTY1290
  • MEMBER
  • 2008 CHEVROLET HHR
  • 2.4L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 220,000 MILES
I keep getting a code p0641 with reduced engine power it's intermittent so it's hard to troubleshoot. Plus, I don't really know where to start. Thanks in advance.
Thursday, September 14th, 2023 AT 4:33 AM

8 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,602 POSTS
So, this code can happen when the PCM goes out or you have a sensor that is shorted causing the PCM to dump voltage. I would remove the camshaft potions wiring connector and use a voltmeter to check the voltage at terminal A in the connector, it should be 5 volts. If not, start unplugging the remainder of the sensors one at a time until you see the voltage return, this will be the shorted unit causing the problem.

The OBD-II trouble code P0641 in a 2008 Chevrolet HHR indicates a problem with the "5-Volt Reference 1 Circuit."

Here are the engine wiring diagrams so you can see the sensors involved that must be unplugged from the system. Check out the images (below). Let us know what happens and please upload pictures or videos of the problem so we can see what's going on.
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Thursday, September 14th, 2023 AT 11:48 AM
Tiny
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Thank you so much. I'll start testing sensors right away and I will let you know.
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Thursday, September 14th, 2023 AT 12:51 PM
Tiny
DSMITTY1290
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Okay. So, I tested camshaft sensor and it get 5 volt but I fluctuates sometimes between 2.9 and 5.0v is my connector bad or is it the ECU? Thank you in advance.
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Thursday, September 14th, 2023 AT 3:33 PM
Tiny
DSMITTY1290
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Also, should I be getting battery power from the other terminal and if so, could that be my issue? Because I'm not getting but 4v.
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Thursday, September 14th, 2023 AT 3:54 PM
Tiny
DSMITTY1290
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Hey back again, it's going straight to engine disable mode I start the car it jumps to about 1,500-2,000 RPMs then engine disabled shut down.
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Friday, September 15th, 2023 AT 8:10 AM
Tiny
KEN L
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When you are monitoring the 5 volt reference unplug the other sensor to see if it jumps if not it sounds like the PCM is bad, you can get a preprogrammed unit by searching Google or Ebay.
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Friday, September 15th, 2023 AT 11:20 AM
Tiny
DSMITTY1290
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Thank you. I'll have to order the new one, but I will keep you updated once it's replaced.
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Friday, September 15th, 2023 AT 2:46 PM
Tiny
KEN L
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  • 47,602 POSTS
Please do!
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Monday, September 18th, 2023 AT 10:13 AM

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