Did I maybe fry my ECM or BCM??

[ScottyBoy]

Yesterday I was trying to recharge my AC after replacing some leaky Schrader valves and O-rings. Compressor wouldn't kick on to accept the refrigerant, so I unplugged and jumped the low pressure switch. Compressor kicked on, so I told my wife who was in the driver's seat, to make sure that the AC was on high, and the rear AC was set to high. No sooner than the fan switch it switched to high, then all hell breaks loose. The blower motor COMPLETELY died,my cooling fan relays started chattering, all sorts of relays through the vehicle and engine compartment started chattering, gauges went wonky, turn signals and headlight don't work, door locks and power windows don't work, damn near NOTHING electrical works anymore. I checked ALL fuses, nothing's blown. I checked battery cables, I checked to see if any engine grounds might be loose.... I'm at a loss. The ONLY thing I did out of the ordinary was jumped the AC low pressure switch. I believe that's connected to either the ECM or BCM, and "could" maybe be the root of my problem? Any ideas?

 

[Joseph Garcia]

Did you disconnect the battery's negative terminal before proceeding with these AC system tests.

 

[OR VietVet]

Did you look for any problems at the relays? I would not think the ECM is affected but maybe the BCM, but I still doubt it. Remove the battery cables and touch together at the ends and let sit for 15-20 minutes. Then reattach them and see what happens. If you did restart the engine after, was there any CEL's?

 

[ScottyBoy]

Yes, I forgot to mention that I did try disconnecting the battery. The relays chattering stopped, but then it all started again after I cycled the ignition. Engine DOES still start and run, but I haven't driven it. I tried 4 times to disconnect the battery to "reset" the system. I even held both cables together for nearly 2 minutes. Symptoms still there. One other thing I noticed, there was a humming or buzzing coming from the AC compressor. Sounds like the little fans on LED headlight bulbs that have fans on them. (No, my headlights on this vehicle do NOT have fans). I unplugged both plugs from the compressor and that buzzing at least stopped. I haven't tried plugging them back in yet because all other symptoms persist.

 

[ScottyBoy]

Did you look for any problems at the relays? I would not think the ECM is affected but maybe the BCM, but I still doubt it. Remove the battery cables and touch together at the ends and let sit for 15-20 minutes. Then reattach them and see what happens. If you did restart the engine after, was there any CEL's?

I did restart it several times afterwards.
No CEL after.

 

[Joseph Garcia]

Yes, I forgot to mention that I did try disconnecting the battery. The relays chattering stopped, but then it all started again after I cycled the ignition. Engine DOES still start and run, but I haven't driven it. I tried 4 times to disconnect the battery to "reset" the system. I even held both cables together for nearly 2 minutes. Symptoms still there. One other thing I noticed, there was a humming or buzzing coming from the AC compressor. Sounds like the little fans on LED headlight bulbs that have fans on them. (No, my headlights on this vehicle do NOT have fans). I unplugged both plugs from the compressor and that buzzing at least stopped. I haven't tried plugging them back in yet because all other symptoms persist.

What I asked is: Did you disconnect the battery's negative terminal (and leave it disconnected) BEFORE you did this work on your truck?

 

[ScottyBoy]

What I asked is: Did you disconnect the battery's negative terminal (and leave it disconnected) BEFORE you did this work on your truck?

No, I did NOT disconnect the battery before charging my AC system. The engine needs to be running to recharge it, so why would I have disconnected the battery?

 

[nonickatall]

Since when must the engine run, wenn you load the ac? The opposite is true, the compressor should not run with low refrigerant.

But that should not cause your symptoms.

Do I understand correct? You just bridged the pressure switch?

 

[S33k3r]

Honestly, if you didn't cook your ECM or BCM -- and I really think you didn't -- I would assume you took out a ground that was going bad. I'd check out that one that goes from the engine to the body in the engine compartment on the passenger side. The fact that everything runs, there is no check engine light, but you are still having symptoms leads me to that diagnosis. And you may not have blown it -- it just might have failed coincidentally.

 

[ScottyBoy]

UPDATE: I got it fixed! I don't know what the "EXACT" issue even was, but I took it to the guy who installed my engine this morning and let him look at it. He was honestly just as baffled as I was. But first thing he did was double check all the grounds, just in case anything wasn't fully tightened or something from the engine install. He hooked up his scanner to it and he was able to do FAR more than I could with my $350 Innova code reader. He was able to pull up old faults from the instrument cluster, and even faults from the OnStar module. Lol! He ended up re-flashing everything and that did the trick. Everything is now back to normal again. He even helped me finish recharging my AC system since I still had the vacuum pump ang gauges and Freon and all sitting in the back of my truck. So now I'm all set, truck running good again, and AC blowing cold again!

 

[S33k3r]

UPDATE: I got it fixed! I don't know what the "EXACT" issue even was, but I took it to the guy who installed my engine this morning and let him look at it. He was honestly just as baffled as I was. But first thing he did was double check all the grounds, just in case anything wasn't fully tightened or something from the engine install. He hooked up his scanner to it and he was able to do FAR more than I could with my $350 Innova code reader. He was able to pull up old faults from the instrument cluster, and even faults from the OnStar module. Lol! He ended up re-flashing everything and that did the trick. Everything is now back to normal again. He even helped me finish recharging my AC system since I still had the vacuum pump ang gauges and Freon and all sitting in the back of my truck. So now I'm all set, truck running good again, and AC blowing cold again!

May I suggest naming your guy/his shop? Sounds like someone we would want to do business with.

 

[Joseph Garcia]

I'd also like to know what scanner your mechanic has.

 

[ScottyBoy]

May I suggest naming your guy/his shop? Sounds like someone we would want to do business with.

He's not an actual shop. He is just a guy who works out of his home garage/shop. He has a pretty decent sized shop behind his house, and he STAYS busy just from word of mouth referrals. The guys at O'Reilly Auto parts gave me his info when I was ordering my engine. O'Reilly was one of the few local places who could get me a crate engine, pretty much EVERYONE else was on backorder with no definite expected ship date. Pretty much ALL the guys at O'Reilly vouched for him, they all said they knew him well and that he does good work and for reasonable prices.
And as far as what kind of scanner he has, I will have to ask him. I think it was an Autel, but I'll have to ask him for the model number and all.

 

[Hobert]

maybe its @iamdub !!! From Li'l Weezyana

 

[iamdub]

maybe its @iamdub !!! From Li'l Weezyana

Sounds like me- shop behind the house, word-of-mouth referrals, personal relationships with the O'Reilly guys and all! I don't have that nice of a scan tool. It is a decent Autel, though. It's about their best one-way model, but still a one-way.

Also, coincidentally, I was in Bossier City and Shreveport today.

@ScottyBoy, I'm glad you got it fixed, and so easily/cheaply. It sounds like, for whatever reason, jumping that switch scrambled the BCM's brains. What did you jump it with- a paper clip? Maybe you were touching something metal in the engine bay at the same time? Possibly while being a little sweaty/extra conductive?

 

[MassHoe04]

UPDATE: I got it fixed! I don't know what the "EXACT" issue even was, but I took it to the guy who installed my engine this morning and let him look at it. He was honestly just as baffled as I was. But first thing he did was double check all the grounds, just in case anything wasn't fully tightened or something from the engine install. He hooked up his scanner to it and he was able to do FAR more than I could with my $350 Innova code reader. He was able to pull up old faults from the instrument cluster, and even faults from the OnStar module. Lol! He ended up re-flashing everything and that did the trick. Everything is now back to normal again. He even helped me finish recharging my AC system since I still had the vacuum pump ang gauges and Freon and all sitting in the back of my truck. So now I'm all set, truck running good again, and AC blowing cold again!

Nice to see a WIN! Awesome!!

 

[petethepug]

Yes, the ability to have two way communication is key. GM is so sketchy about owners having access to their lucky charms or Tech2 capabilities that they’ve almost shot themselves in the foot.

Fortunately, the guy who invested in his programming capable Tech2 was vindicated by its little known capabilities. You got styled by someone who is having a frick’n blast with the keys to the kingdom.

 

[RET423]

For posterity sake, when you need to use the AC compressor to fill an empty system (because you don't have access to an AC Machine) the way you do it is to remove the AC relay from the fuse box and jump the pins with a paper clip (usually pin 30 to pin 87), this bypasses the high and low pressure cutout switches so the compressor will run and draw in the freon; once you get enough freon in the system to keep the low pressure switch from cutting off the compressor (about 25 psi on the low side) you can remove the paper clip and reinstall the AC relay to finish charging.

Simple and safe for the system, some systems combine the high and low pressure cutout switch into one switch which means a simple jump wire replaces the expected resistance on the circuit with a dead short. There are protections that might allow the system to survive this short (sounds like yours recovered with a reset/reflash) but jumping it at the relay prevents that from happening.

 

[swathdiver]

UPDATE: I got it fixed! I don't know what the "EXACT" issue even was, but I took it to the guy who installed my engine this morning and let him look at it. He was honestly just as baffled as I was. But first thing he did was double check all the grounds, just in case anything wasn't fully tightened or something from the engine install. He hooked up his scanner to it and he was able to do FAR more than I could with my $350 Innova code reader. He was able to pull up old faults from the instrument cluster, and even faults from the OnStar module. Lol! He ended up re-flashing everything and that did the trick. Everything is now back to normal again. He even helped me finish recharging my AC system since I still had the vacuum pump ang gauges and Freon and all sitting in the back of my truck. So now I'm all set, truck running good again, and AC blowing cold again!

This was a job for a Tech-2, not the Innova.

 

[petethepug]

To program with a Tech2, you can longer purchase the Tech2 as a standalone device anymore.

The Tech2 software integrated into a WIN 7 or 10 laptop is needed, along with the MDI device or the VX Nano which is really finicky until you learn all the work arounds.

To program a GM device on the bench, like a BCM or other new, off the shelf device is something I have no idea on what is required.