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Transmission issue

2003LANCHE

Full Member
Joined
Oct 3, 2021
Messages
9








Hello everyone let me start off by saying my 2003 Avalanche has 290k miles. I bought it 5 months ago it's a 1 owner never in an accident. The transmission has slipped since i bought it and have recently got around too having my mechanic entirely rebuild the transmission for $1300. Considering im having an electrical issue it's worth noting that it has an aftermarket stereo (has worked great no issues). and the driver side door lock actuator has not worked. I replaced it and it didn't fix it. I thought it had a short in the driver's side door and didn't want too mess around with the wiring as it does not bother me too much having too use the key too unlock the door. (Not sure if this has anything too do with anything but) I have got the "Battery not charging" message since i bought it and have learned too ignore it when it periodically comes on. My mechanic has checked the battery many times and alternator is brand newish so its not that. 200 miles after driving with my new transmission i have noticed the transmission would slip into 3rd when going about 70mph and sometimes just would not shift back into 4th at all unless i stopped using the vehicle for 20-30min. Check engine light was on for the shift solenoid D and Transmission fluid pressure switch. after a few days of using it here and there the transmission lost all gears except park (Thank God I was at home) my mechanic came over and dropped the pan, replaced the Transmission fluid pressure switch, put the fluid back in, told me too start it up and put it into gear. I had a working transmission again! 2 days after that today i get the check engine light again for the same code. So im pretty sure whats going too happen next... im scared too drive it now that its acting up again. Fuses relays are all fine i checked them first. I really want too fix it the plan was too keep it forever and ever i have wanted an Avalanche ever since I was a little boy and im so sad that i can't even drive it :( im beside myself just thinking about maybe having too sell it. dont know what too do now or what too look for if you have any suggestions at all on what too do next PLZ leave a comment.
 
I don't know too much on your transmission issue hopeful you or mechanic can figure out. My 07 I switched out all solenoids when I dropped transmission pan to change fluid and filter.
I would try solenoids & or wiring harness controlling solenoids?
Also you could try checking the battery/frame ground points on Avalanche see if can clean/sand/wire brush. My alternator had some charging issues mostly hot days running A/C.
I bought new battery ground sensor before cleaning connections making sure bare meatal tight contact. Since I purchased it still replaced old sensor, had to remove ground frame points to get sensor on so cleaned and tightened ground points same time.
It helped very much I also noticed after getting new agm battery when battery has full charge the dash voltage can drop from 14V to about 12v. My battery not charging message dosnt display but my 07 seems to be charging much better since.
Your door lock may be a bad connection or broken wire in-between? Harbor freight has cheap ohms readers can try testing pins from door connector to ?Idk? Would research where lock controls go.
I would think most is in driver door as my 07 has controller for all windows and doors I'd think it's inside that?
Good luck 👍
 
1st thing I'll say is that is a nice lookin' truck

AS for your transmission woes, I have little advice, I have no experience rebuilding automatics, solenoid packs seem to be what they default to replacing.. Rebuilding a manual gearbox, I've succeeded doing that a few times.

Your door lock issue, I'd put 12v right to the lock motor, if it works, I'd suspect the DDM (drivers door module) or the wiring from the DDM to the door lock motor. The DDM is the switch and electronics assembly (on your door) that operates the mirrors, windows and door locks. The DDM is one of the many overly complicated electrical devices that GM put on our vintage trucks that wear out. The good news is disassembly and cleaning of the DDM is not too difficult and you may succeed. Better news is the DMM is even easier to replace, junk yards get around $40 for a working DDM, new they run about $125.
 
I agree with the above for the door.

As for the transmission, it sounds like you need to give it back to the mechanic and have him fix the problem. Unless he's gonna tell you that your trans harness going from the transmission to the computer is damaged, everything else comes down to the transmission and what's inside it.

The electronics usually get replaced in their entirety when a transmission is overhauled by someone that knows better. The solenoids, shift switches, wiring harness, ect. All of that is sitting right in the pan. If you're taking her down to gut it, it's only another hour or so to swap the pan components.

As far as I know, P1810 is given when the computer cant decipher what gear the transmission is currently in. Be that a strange pressure issue from a solenoid, a wiring harness issue impacting the signal of the pillow switches or solenoid, the o-rings on the pillowswitch being damaged/ missing, or even metal flakes shorting out the switches if the pan wasnt totally cleaned out when it was rebuilt.
 
You said the mechanic replaced the pressure switch, and you still have the problem.
Notice how the code description reads "Transmission Fluid Pressure Position Switch Circuit".
The switch is just one part of the circuit. Apparently, the switch was not the issue.
The rest of the circuit needs to be addressed as well. Could be a poor connection, or a short to ground occurring.
Unfortunately, that is the problem with owning a computer controlled (newer) vehicle.
Any connection issues in a circuit will cause voltage drops, and the computer will not receive the correct signals as a result.
Hence the old computer saying "Garbage in, garbage out".
The transmission is not working correctly, because the computer controlling it is not receiving the correct electrical signals.
The computer then does not know how to respond, since it is now attempting to operate outside its normal parameters.
In short - if the messages are trash, operation will be trash.
I would start by getting a good diagram of that particular circuit, and then check it one piece at a time.
(As Johnny Cash used to say...sorry, couldn't resist >:D)
Wiring connections for a computer controlled circuit must be 100% good.
Take apart connectors and clean off any dirt or corrosion. Make sure the pins are not bent or loose fitting.
Check wires for any chafing which would cause insulation loss and a short circuit.
You said it will work fine again if you stop using the truck for about half an hour?
Perhaps there is a connector or a wire harness somewhere near a source of heat that is damaged and making intermittent contact with ground, when it shouldn't be. Anything stupid like that.
Hope any of this helps you narrow it down. Good luck!
 
I agree with CarMech. It definitely sounds like a wiring issue instead of a mechanical problem. In my previous life I was a GM Master Electrician, and when I had multiple weird electronic problems happening at the same time, the first place I looked was ground circuits. Find a good wiring diagram and locate all the grounds, unbolt them from the frame/body/engine and clean them well and reattach them. Concentrate on PCM grounds, as this could also be related to your charging message. Our trucks are getting older, and depending on where you live, corrosion in electrical circuits is a huge problem. Hope this helps
 
I agree with double checking electrical, my 07 grounding wasn't making great connections caused random check engine codes all over the place.
The main battery grounding came loose & codes list a mile long thought computer system was going out.
I've added grounding points to try avoid future grounding problems.
My torque converter has been slow grabbing & releasing at stops. Feel kick if try accelerating fast from stop, see rpms drop 500 & slightly under until release neutral then RPM goes back to normal.
Just got Thor converter in mail plan to remove old torque converter & hope the new converter fixes the issue.
 
I found many electrical spots were questionable on my 07. Recently was grounding wires to engine lower drivers side engine near motor mount.
X3 wires into x2 heat shrink with glue or epoxy Inside.
I'm still getting the same code you were getting.
My pressure switch and all solenoids & transmission wiring brand new.
I'm about to try a new TCM only I salvaged one from 07 suburban at pick a part. I read they need to be programmed by Vin/to work.
Wiring pages I've found & bought don't have enough details.
Hayes book dosnt show transmission to TCM. The other internet pages printed show wiring but not if any connections or junctions between transmission & tcm.
I believe the drivers left foot junction box could be a problem between but I can't be sure by diagrams I've seen.
Anyone know if wiring has a junction? Between transmission plug & TCM.?
I salvaged a junction block from 07 avalanche at pick a part aswell believe that could be a junction causing issue if it's between transmission & tcm
 

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