SUCK FEST!!! Boys, pray for Ben right now.
I have seen pro people fight this for days and days on Gm. Working in chevy dealership guys yell at each other a curse: “2770s to you and your kids!” People sell trucks cheap over this. Strongly consider a dealership over this and be very clear, get it in writing that you pay NOTHING if the problem is not resolved. Be sure to get that in writing if using any kind of private shop, and expect small claims court to get back your money. I have seen new ecm, bcm, transmission, transfer case, harnesses all thrown at this trying to end it. This problem put more gmt800 into ‘lemon law’ situation than any other that I know of. But since you been fighting it this long- sounds like you won’t quit, So....
This is a descent video showing how to load test a battery with a multi meter. But it really is not a proper load test because bad cables, bad starter, loose connections, etc can have a person condemn a good battery. Showing because people jump to this method because it is simple but this should not be your method for this scenario. Store it in memory banks, but move past it for your issues currently. You need EVERY TEST to the highest degree of accuracy, as you might have 6 tiny issues adding up to one problem.
However some key things to point out. There are many cheap multimeters, and many do not read accurately the Fluke 87 in this video is the one to get check around for best prices and get ready to cringe- $400 is a great price. There is reasons pro mechanics and pro electricians use this meter and are happy to pay that price. Get a cheaper one and misdiagnosis is frequent. Used to be when teaching people I said buy once, cry once . Now, I steer diy mechanical people away- USUALLY. Getting a power probe 3 kit is a bit cheaper and is far better for working on vehicles. But you are caught in an unusual situation- you are fighting p2771,2,3,4 etc code issue- and it is commonly a nightmare fix. You will probably buy the fluke 87 and power probe3 before this is done. If you have already spent hundreds at shops and are determined to diy this- understand you will not learn this and buy tools for under $600 by what I seen so far in this thread. If you don’t have a TOP NOTCH scanner- add another $1,000. You NEED one on this problem.
This is battery load tester. I bought this same basic unit almost 30 years ago, and used mine as a pro mechanic for many of those years. It still works fine.
Amazing deals on this 100 Amp 6/12V Battery Load Tester at Harbor Freight. Quality tools & low prices.
www.harborfreight.com
Do not buy any other electrical testing tools at harbor freight. Their multimeters are complete garbage. The power probe and fluke 87 will do everything else you ever need to do.
buying this is far better for Proper load test is disconnect cables and test battery separately. to test battery cables you can connect to the end of the cables, but often have to have the cables removed from the starter to do so just for accessibility. You will be doing both.
You need full schematics with pin outs and location listings. A subscription to all data is probably in you future. I say probably because maybe guys on here know of something better for chasing electrical that came out since i quit working pro? Anyone?
Do you have good pin out tools yet? If not, add them to the list.
I will warn you not to throw parts at it, new defective parts happen and complicate the issue. Say there is 3 bad connections and 1 bad sensor you have as original problem. You swap a different sensor that was good for a new defective. Now you maybnot find the bad connections, or the other sensor without complete disassembly and all individual testing. I have seen pros throw multiples of the same part chasing issues. You need to fully test each component as you go.
You WILL BE removing EVERY ground in the vehicle and cleaning/ repairing them. I can’t remember how many in cabin, 5 i think. 20ish in the rest of the rig. If the truck is rusty- you are toast and best bet at this point would be 6 awg ground wire from battery daisy chained to each ground point. It HAS TO go in one direction closest to battery first, farthest last. Grounding condenser might be needed. Note I do not recommend this in vehicles usually because of ground loop possibilities and the host of problems it can create. Do not do this in the beginning, this is a last ditch effort after you have replaced your primary harnesses, ecm and bcm.
If this is your daily driver-quit. Buy a rust bucket or moped and drive it for now while fixing this. Expect to completely remove a few electrical harnesses from the vehicle for testing and inspection.
Fight your way through this, and you will never fear auto electrical the rest of your life.
All this said, and sometimes it is a bad transmission, transfer case, etc.
