tranny in a 2005 gmc sierra 1500 5.3 v8 flex

desonie45

Original poster
Member
Apr 21, 2015
9
my check engine light came on it gave a code po785 i changed my shift solenoids truck shifted great for about an hour light came back on thank it was stuck in 3 not sure took it back to shop cleared the cods truck runs great did this three times i also have a abs sensor out on drivers side i checked all plugs everythang looked fine. were u plug in the code reader the fuse burnt up dident know it and the truck ran good all day i put in a new fuse and truck back into limp mode any ideals iam no mechanic but i do it my self if i can air bag light is on, sometimes service 4x4 messages comes on i put new fuel pump in new plugs an wires there were more cods that cam up but dot remember what they were something with ignition switch it works fine something about my air intake abs sensor can any one help?
 

Sparky

Member
Dec 4, 2011
12,927
Ummm ok

It sounds like you have some real electrical issues. Not sure if the Sierras had the same ignition switch issues that the GMT360 platform did, but if so it may be worth swapping that switch out. Just because the truck starts doesn't mean the switch works fine.

Other than that, you may need to get some scan tools on the data bus to figure out what the heck is going on.

Also, PLEASE use some punctuation and grammar in your posts. It is very hard to read what you wrote down and make full sense of it.
 

desonie45

Original poster
Member
Apr 21, 2015
9
Changed my ignition switch truck ran good for a while and had one thing go wrong. The truck would not shift out of third so i shut truck off and restarted it and it shifted fine all day. I noticed my battery will read below 12 and sometimes above 14. When its above 14 it shifts great below 12 it shifts a bit hard.If there is not enough power to tranny will it cause it to shift bad. once truck is worm there is no issue. After i changed ignition switch truck ran a lot better , but still a small issue don't thank tranny is getting enough power could that be my issue.
 

desonie45

Original poster
Member
Apr 21, 2015
9
Not sure how old battery is but i will go have alternator checked. It wont shift right unless truck is worm, and after it is worm i have to shut truck off let it set for a min and then it will do fine all day.
 

desonie45

Original poster
Member
Apr 21, 2015
9
Ok they checked my alternator at auto zone and it failed, so i changed it and drove off. my battery gauge started to drop so i took it back to auto zone and they tested new alternator and it failed. put my old one back on and it passed. The battery also passed. when i first start the truck the battery gauge reads above 15 in about 5 minutes it will drop below 12. it does this continually with or with out a new alternator. seems like something is pulling to much power, I pulled fuse to radio nothing happened.

My main concern is in the mornings it will shift a bit hard and then goes to limp mode. Once truck is worm i turn truck off for a min or two start truck back up and it will bun the tires off the truck.it shifts great. I put in a new fuel pump,new shift solenoids, new oil pressure gauge,new driver side abs sensor,new ignition switch. i checked all plugs to transmission they all looked clean. Also changed spark plugs and wires.
 

desonie45

Original poster
Member
Apr 21, 2015
9
There was a fire in the truck and it burnt the head liner. The owner before me put in a new liner and he said he taped off all wires.I have no lights on the selling. I test drove the truck before i bought it,it drove great, 350 miles later all the problems started. i have owned truck for 14 days as of today.
 

Sparky

Member
Dec 4, 2011
12,927
There was a fire in the truck? Ah man why didn't you say that earlier...

You very well may have wire(s) grounding out someplace, circuits damaged, etc. That's going to a job to sort out...
 

desonie45

Original poster
Member
Apr 21, 2015
9
yea fire in the truck, i trusted the guy i bought if from that he fixed everything. does the head liner come down easy? never taken one down before.
 

desonie45

Original poster
Member
Apr 21, 2015
9
I found all my ground wires that go from battery to frame and battery to alternator and they were corroded. I cleaned them off and my battery gauge stayed the same all day.But i noticed when i let the the truck idle in park for a while it started to drop,I turned truck off restarted truck and it went to normal. I went and bought a multimeter and checked battery and alternator everything checked out. This morning the truck was stuck in 3 gear for about 5 min. I pulled over turned truck off let it set for a two mins.Turned it back on and it shifted better than it ever has. I checked all wires i could find they were good. There were some burnt wires above the headliner,as far as i could tell they were not connected to anything. Getting closer to finding my problem. I changed all my shift solenoids but did not change the TTC. I may go ahead and do that!

Could my speed sensor cause my shift problem even if my speedometer is working fine?
 

desonie45

Original poster
Member
Apr 21, 2015
9
thanks gingerbread man. I will be checking my lines out in morning. Is the tranny cooler part of the engine cooling system. Whats strange is that it shifts fine when the truck is at proper temp. it stays in 3rd until its warm and after it is at proper temp i have to pull over turn truck off let it set of a min or two restart truck and it will shif great for the rest of the day. Even in the middle of the day if the truck cools all the way down it will shift fine.only does it after truck sets for 5-8 hours. But i will for sure check these items out. thanks any other ideals will be appreciated..
 
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desonie45

Original poster
Member
Apr 21, 2015
9
Ok well I took my throttle body apart and cleaned it, it was extremely bad and also cleaned my mass air flow sensor truck ran like crap for an hour. The next morning I let truck worm up before driving and no shift problems at all,check engine light gone. So was that my problem? Well I changed all shift solenoids, my fuel pump because it went out, oil pressure gage, plugs and wires took every ground wire I could find and cleaned them, there was a fire on the head liner took all wires out inspected them found a two wire plug burnt up, and took all bad factory tape off wires and installed all new tape. New oil and filter. Tyranny filter and fluid. I have only had truck for 20 days. I hope I don't have to do any thing else to it for a while, I do plane on putting on a combo lift only 4 inches and put some 33 inch tires. Does any one recommended a good lift kit or am I asking for more problems buy putting a lift on?? I do go off road only for hunting reasons not to raise hell. My truck is my office I work for a storm restoration company and I am in it 8-10 hours a day and I wont it to look as good as I can make it.
 

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