Code P0641, causing reduced engine power?

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." This reference voltage is important for various sensors and components in the vehicle's engine management system. This guide can help if you need to replace the PCM

https://www.2carpros.com/articles/how-to-replace-an-automotive-engine-computer-pcm-ecm-ecu-a-comprehensive-step-by-step-guide

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.

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.

Please do!