OK, time yet again to ask the experts! I have a '94, W code 4.3 Vortec (CPI). My transmission is really pissed off. It's the 4 speed auto with OD. and I have no first gear, and I have to shift gears manually, won't do it automatically. I have the OBD-1 and am throwing a code 81!? Can't find that code listed, so can any of you out there in Blazer land shed any light on this weird little bit of foolishness? Starting to think this thing is being possessed by evil gremlins.

 

Book says:

DTC 81 - 2-3 Shift Solenoid Circuit Fault

The PCM provides a ground to the solenoid. It will set the code if voltage remains high for 2 seconds if commanded "ON" or if voltage stays low for 2 seconds if commanded "OFF".

Can you OBD-1 do the factory tests that the TECH-1 can do?

Electrical Diagnostics & Driveability Manual
SECT 10A - 10A-56 (just for my future reference)

 

Thanks for the info! I was hoping the code didn't mean the dang thing was ready to explode! I am only able to do the paper clip jumper on the OBD-1 to pull codes, so I can't do the TECH-1 factory tests. I had a weak battery, and have replaced it, but the tranny is still not shifting, so it looks like the solenoid itself may have failed. Is there a test I might be able to do myself to determine if the unit is faulty, using a multimeter? If the problem is with the solenoid, maybe I can actually keep some of that stimulus money for myself, and not give it to a mechanic!

 

You may invest 25$ in the CD rom with the factory service manuals and electrical and diagnostics. try rockauto, they have it for the 94. Mind you, not the Chilton or Haynes.

I'd go for the wiring first. Try checking for continuity from the PCM to the solenoids. Most of the time it's just connectors and wiring. Broken, scuffed, shorted. Especially that it stays in that gear "could" be an indicator of a ground somewhere. Finally for the solenoids. May need to pull some information on the internet to figure the resistance of the solenoids.

Maybe our Trans Gurus here in the forum have some testing to offer.

 

Well, that is good advice. I should get one of those CD's. I already have a Haines, but that was almost a waste of money. Not much useful stuff there! After a bit of research, I think I have a plan of attack. Considering the symptoms of my problem, I suspect a wiring issue, since it seems unlikely to me that every electronic component failed at the same time...I do not have any automatic functions, no shifting up, or down, etc. Since this is my daily driver, I will test all the external wiring, before opening up the tranny. I want to be able to have everything on hand and ready to install if I have to go inside, so I only have to do it once. Thanks, once again! You have been a huge help!

 

Thanks for the compliment. We try hard to accommodate.
I think it's a good way to go from the simple to the more complex. Checking the wiring on these old trucks most of the time already solves the problems, especially with electrical. We need not forget that they are over 25 years old now. Mechanically they are solid, until somebody neglects it or tampers with it or brakes it. Electrical stuff is IMHO not that solid. Lots and lots of loose wires already in OEM wiring.

When doing my engine swap I'll do some electrical stuff at the same time. Get longer looms in the engine bay to clean up some of the OEM rat's nests. Then the ECU wiring will be additional to the OEM stuff.

Good luck with that fix of our tranny. Once you have fixed it, you could post the results, that would be nice to have another "SOLVED" thread.

 

I will update you all when I get this thing fixed. I'm going to get after it over the weekend. It's always helpful to others to find out what the problem was, and how to fix it. I know I have found many answers here, just by searching threads. Last resort for me is to ask the questions, and risk looking like a complete mechanical moron! LOL!

 

OK, here's where I'm at with my tranny. I have checked all wires on the external wiring harness, from the ECU to the connector, and have continuity in every wire, so it looks like the harness is good. I would like to check if this is a grounding problem before I open up the tranny and start on the solenoids, but I'm stuck. I discovered in my research that I'm stuck in Failsafe mode. I have reverse, second, and third gears, but can only shift manually. So, I would like to know if any of the internal components are grounded externally somewhere, and if so, which wires are the correct ground wires to check, and where would I find the location of the wires? I haven't had any luck finding this info, so I am counting on this forum, and the wealth of knowledge you all are just waiting to share! Thanks for any help, it's always appreciated!

 

I'd start with a visual check on all the wiring even using a little mirror on a stick. Maybe somebody here at the Forum has the troubleshooting guide for that transmission.

 

Any Luck? I'm not sure about any external grounds. I just looked in my ATSG Manual. . .for 2nd and 3rd it only lists the 1-2 Shift Solenoid and/or circuit, or Sediment as possible causes. When was the last time the trans was serviced?

Sounds like you need to just drop the pan, if you haven't already. My valve body wiring harness was pretty nasty and disintegrating when I opened mine up, so that could be the problem as well.

I don't think I saw error ask. . .was there anything that happened leading up to the problem? Any work done recently before it started?

Here is a link to the Rebuild Manual error_401 gave to me when I was working on my trans. https://drive.google.com/file/d/14ho...ew?usp=sharing
The Valve Body section that starts on pg 133 is prob what you'd want to look at. There's a tech bulletin on pg 143 that gives you the resistance for each solenoid, and tells you which pins on the harness connector go to each solenoid.