This evening my car suddenly gave me warning messages, Engine Power Reduced, Traction Reduced, Service Traction, Service ECS. I limped the couple miles home under severely reduced power and pulled the OBD II code of P0641. The Chilton's manual says this is 'Sensor Reference voltage A -- circuit open'. Poking around online I keep seeing references to the ECM, but I don't know how I could test this at home before spending hundreds to replace it.

Can it be tested if I pull it from the vehicle and take it in to a shop (assuming they have the right computer for this vehicle.

2008 Chevy HHR, 2.4L automatic

Thanks in advance, car Yodas.

 

I'd be double checking the ground wire connections to the transmission, rad cradle, and such.
I would also urge you to have a look at the fuse box under the hood to see if the halves are tight and secure to each other, and the fuses and relays are firmly mounted.
Also how old is the battery, are the terminals tight and clean?

 

Not sure on the battery, I've only had the car about a year and a half and it's the one that came with it, but the connections are squeaky clean and tight. I do have a <year old battery that I could throw in there if necessary. I was going to pull the connections off the ECM and make sure they're clean, but it's like a Chinese puzzle and I haven't figured out how they come off yet. Chilton's has been of no help whatsoever, the photos it has of the ECM and connections aren't even what my car looks like.

Thanks for the tip on the fuses. I'll have to look up where to find the ground wire connections but that should be easy to find online.

 

This is what Google found for me.
P0641 Chevrolet 5 Volt Reference Voltage Incorrect OBDII Engine Light Trouble Code | Engine-Codes.com

A reference to something does not mean it has anything to do with it.

Chilton's has always been of no use to me. Google is great. Check out the links in my sig.

 

There are no ways to field test an PCM removed from the car. There are shops that rebuild them but they are not always available to the general public.

I myself would not be so fast in condemning the PCM. The PCMs do fail but it's not a common as people think.

There are a lot of techs out there that replace the PCM then find that wasn't the problem. When you see a repair bill that has a PCM replacement and mutable other sensors chances are the PCM didn't fix it so the tech Finally found the faulty sensor or wiring problem.a PCM is not returnable.

Your code states the 5 volt reference was shorted or lost. Any sensor on the 5 volt reference loop could have shorted or a wire shorted and that code would be set.

When the PCM looses the 5 volt reference it will not see any of those other sensors as reliable.

The first thing I would do is disconnect the battery for a few min. And reevaluate the problem.

 

I disconnected the negative cable on the battery (should I have done both?) for about 30 minutes last night, and went through the fuse box making sure the fuses and relays looked good. A couple of the relays moved a negligible amount when I pressed down on them, though I wouldn't have thought it would be enough to generate an error code. After I reconnected the battery, I drove it for a couple miles and it seemed better, and didn't have the error messages anymore. I drove it 6 miles to work this morning without the code showing up again.

Bad thing is, next weekend I have to drive halfway across country, from the midwest out to the west coast and it would really suck for it to break down in the middle of the summer-heat desert.

Anyway, thanks for the tips, everyone. At the very least, they got me to work today, so that's something Sometimes I really miss the days when a car could be fixed without a $30,000 diagnostic computer at hand...

 

Are the fuse panel halves tight?

 

You mean the lid that covers the fuses/relays in the engine compartment? If so, yes. If not, then I'll have to take a second look when I get home this evening. Or is there a second fuse panel somewhere that I need to check?

 

No just the one under the hood, remove the lid you will see four bolt heads gently tighten those up, I believe them to be 7 mm
Look down to the right of the oil filter housing to see a stud with black wires connected to it that is the ground for the trans and engine.
Look to the right of the rad on the rad cradle you will see a wire connected to a stud there, it is also a ground wire ensure it is tight and clean.

 

Easy instructions, thank you!