No communication

Check fuse HVAC CTRL BATT located BCM underdash right of center console near dash. Also here is the ALDL wiring diagrams below with a guide to help check it.

https://www.2carpros.com/articles/how-to-check-wiring

Check out the diagrams (Below). Please let us know what you find. We are interested to see what it is.

Okay I went through every fuse in the car, none are blown

I did find a location under the hood that says ecm batt 10Amp but there is no fuse there (it is location 51).....it only has gold connectors only on one side of where the blades plug in, so it looks like just a spare socket...just weird because all the other locations like that say not used....

The car is just running real sluggish since the check enigine light has come on and now I cannot read the codes.....Any more advice would be great...THANKS

That is weird because the fuse panel skips over 51 check out below.

Thanks...Yes I checked this fuse panel yesterday also...All my fuses were good. my data link connector under the steering wheels only has 6 wires can you send me a diagram of what voltage or routing these wires should go to so I can check for open circuits..If you think I need to go a different route, just let me know .....Thanks for helping me...still kinda confused if the data link connector is for the ECM or BCM

Only wire with power is Red/White taht is powered by the fuse you checked. The others are Lan serial buss and a ground.ALDL connects to BCM then ECM and 11 other computers. What type scanner was used? tried several?

Thanks man, you are great....Yeah I tried several and even took to the dealership and theirs would not work. They want to charge me by the hour to now trouble shoot the electrical system. I got under there yesterday and look at the data link connector and it only has 6 wires, does that sound right?

yes one power two grounds and three to BCM. If I where to guess think BCM is suspect

When I get home today I guess I will check these wires, what voltage should I be looking for on the red (prob. just 12 volts)

Thinking maybe should I check the large locking connectors on BCM

Tan/Black wire from ALDL goes to BCM terminal #1
Tan goes to BCM term #19
Both black ground
Red/White 12v

Man thanks so much , I will try it when I get home

This is a 2008 4 cyl, so I am not sure if that makes a difference. I swore I saw a green wire in the harness but not for sure. I will try it when I get home

Hey Doc
I checked the red wire 12 volts strong at that point and both grounds are perfect. There is a green wire , would you please look up that for me (location termination). Also on the BCM terminals I did not see any numbers, how is the numbering scheme for this terminal block (left to right?) Thanks a million

I checked the tan wires (2 of them)and a green wire from Data link to the bcm panel (see pic)...no continuity on them no matter what I did. I had voltage on red pin and ground on both blacks. Do these tan and green wires go straight to BCM or should I look for a connector along the way

They go straight to BCM found green wire from data link to BCM from pic looks like that is right location. Unplug at BCM and check what OHM scale using?

I took the J2 blue connector off of the BCM (see example pic) and pinned it out and I have continuity straight from the data link to that connector, so it is getting signal. At this point Do you think replacing the bcm is even an option

I wish I knew if it was just a sensor to replace causing this sluggish acceleration because that is all that is wrong with the car since the check engine light came on and I would take a chance and replace something minor, if I could find out what commonly goes bad on the G6 at around 60,0000 miles

Replacing BCM would be next action it interfaces with PCM and all other processors . Try this disconnect battery for several hours see if it clears light

If I buy another bcm does it have to be flashed for my car or is it just plug and play. I guess I need to make sure it is the exact same GM part #?? (see pic) I appreciate it so much and even though I am still so frustrated over this car, you have helped keep me calm..I also did the battery trick last week and it still ran crappy but the light stayed off for two days then came back on

Yes new BCM must be programed. When BATT reconnected and MIL off did driveability improve? is reduced engine power on? Did dealer suggest relearn of BCM?

I got some different news!!! I worked all weekend, checking this and that... I found the female pin of the red wire on the data link plug looked bent up inside where it would not make a conncetion with the male scanner plug. So I bent it down where it would make a connection, drove back to the same autoparts store, same scanner and it linked up first time and read the car!!! The only problem is the dealership cleared the check engine light last week so the scanner says "no check engine light detected" "more drive cycles required. So now hopefully the light will come back on, not sure how they cleared it but everytime I cleared it with the battery trick it would come back on in 2 to 3 days. Let me know what you think about this new revelation

You did good bent pin not common but sure would keep from linking. Was not sure that BCM was at fault after you cleared all wiring. this is good bit of info to remember when next non com comes up. if MIL lights up post code and will give it a go

I honestly prayed before plugging in the scanner this morning :) Here is what code I have: P4020 - Catalyst System Efficiency Below Threshold (Bank 1).

Code states CAT operating below threshold level. Need to clear and see if it resets up to three drive cycles. Also check physical condition of exhaust ans CAT and O2 sensor wiring. We are looking for any other codes to show up. How is engine running?

The engine runs sluggish on start and eventually evens out around 50mph. Noticed also when at idle you can rev it up to 4K rpm and put it to the floor and it stays at 4K (not even close to redline)
I am hoping just 02 sensors....

Believe CAT is particaly blocked by sluggish accel and standing rev to only 4K

so do not waste money on 02 sensor??? (bank 1 ) downstream sensor is around $40

No need exhaust back pressure test done to verify replacement of CAT. O2 is not going to cause problem and would set a different code. Remove front O2 if engine revs higher the CAT

Is the cat failing a common problem with this car (I got 68,000 miles) Where can I get a back pressure test done?

CAT can fail for various reasons such as leaking fuel injector, engine miss, overheating, incorrect fuel additive.
Most shops can do test very common to check out suspect CAT

Hi, so I have the same problem going on with my car, same make, model and year. I went to get inspected and there was voltage but no connection. Had it checked and the guy said it's more than likely my ECM. All fuses worked except 2 but he said those aren't powered? There were (2) 10 volt, not sure what numbers though. But he said it's a bust or something. I guess everything on the dash. I'm really hoping it's not the ECM considering it's very costly. Any advice would be great, thank you!

There is a fuse that runs the self diagnostic system. Here is a guide and a wiring diagram so you can see for yourself and then check the fuse. HVAC control

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Please let us know what you find.

Cheers, Ken