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4L80E shifts too soon and bogs down until I shift manually through all gears and then shifts fine on it’s own

Ben Watts

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Good evening,

2002 Chevy 1500 HD with a 6.0L engine. I posted about a year ago and still have not found a solution to this problem. Hopefully you can help point me in the right direction.

The only code that comes up is a 4wd low circuit code and my 4wd service light comes on periodically, but only about once every two weeks. I have found some articles stating that the 4wd low circuit is on the same circuit as the transmission going into the PCM so I don’t know if this has anything to do with it. Below is what I am experiencing.

When I crank up, I have to go through the gears manually while driving. Once you go through all gears 1 through D, and reach about 55 mph, then the gears will shift smoothly on their own from a dead stop.

If I don’t go through all gears manually first, and try to take off in D right after initial crank up, then it will shift into the next higher gear too soon and bog down. If you try to push the gas to the floor it will not downshift.

However, if I run through the gears manually first and get up to 55 mph then stop and can floor it and shifts like it should.

Any suggestions would be helpful since I have been dealing with this for over a year now.
 
Have you cleaned the grounds? Load test the battery - we don't care how new it is or isn't: it's test time. What is the voltage before the first startup of the day? Offhand OnStar, a known battery parasite, is analog for 2002 and forever looking for a signal that ain't there anymore.

Shared circuits share problems. Say if you are shorting the 5 volt supply to a bunch of sensors, well, all the sensors are now INOP due to no 5v to em. Offhand I don't know if 4x4 has anything to do with it. But, Plausible.

How often do you shift in/out of 4x4 and when was the last time? If this is an electric shift 4x4 the position contacts get dirty. Shifting it through 4x4 low several times may help. Or instantly get stuck in 4x4 low and stay there... There are several other problems with the 4x4 system and controls. Bluntly I have a 4x4 shifter on the floor in my newer 2018 because even in the future nothing works. Keeps the electronics down.

Is the front diff leaking on the driver's side? I had the one in our 2002 rebuilt twice with the leak the only sign it ground itself up. 2nd time was under warranty...

On the 2002 5.3L there is a TSB to cut the "sense" wire going to the alternator regulator and put it to the output lug on the alternator. Noise or an interaction on the long sense wire before, during, after, a shift (or what the hell ever) confused the ECM and screwed up shifting. It was a common enough problem the dealer asked me about it vs. me complaining for them to trip over the TSB.

Quick and dirty is to pull the connector on the alternator (so it like ain't working making noise or charging) and see if the shifting problem is still there. No? I would test the alt for noise like bad diodes or open windings before cutting and moving the regulator remote voltage sense wire.
 
Thanks for reply. I will search for all ground connections and will have to a purchase a multimeter to load test the battery.

If anyone knows the location of ground connections for the 6.0L, 4L80E that would be very helpful.

I will post again when I have more information. Not sure when I will have time to check these various points.
 
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.
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.
 
That is an excellent post @Will L.
Especially about the multimeter. I have a multimeter that I have been using for years, bought from Northern over at Havre when I went to a diesel school. I thought it had been doing me well, wrong. The other day needed to test some voltages, readings were real low. Told my friend he should take it to a shop and get the test done. He did and voltages were where they needed to be.
Guess this old thing will be finding the trash bin, then, once again I will be begging for forgovness from the wifey. 😳😩😹😹😹😹
 
The worst thing ever is when people use cheap meters checking higher voltages. Many people die every year from it.
The meter would say it is good for it, but then they fail- sometimes in an arc flash (mini explosion).
Y’all wanna see a horrible way to die, learn about arc flash. Often takes weeks to finally die after having had copper blown up into tiny particles hotter than the sun fly into your body, often lighting your clothes on fire. Many folks think the 120v in a regular house isn’t a big deal, or even 2-3 car batteries that feed an rv. SMH
 
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