The wife and I just bought a 1994 Sierra 1500 4x4 5.7 122,000 miles. we got a good price on it since it has a few issues.


Right now the speedometer does not work (rest of the gauge cluster works fine) and the trans won't shift higher than 1st and sometimes 2nd. Now before posting this I've spent some time searching the forums and saw that alot of time the VSS and ignition switch was involved in this problem. I replaced both and the problem has not been fixed.

I'm going to check the wiring from the VSS harnes and follow it as far as I can to check for any breaks or fraying. Since the trans had been replaced with one that came from a salvage yard I thought maybe some wiring got cut or broke in the swap.

I also read in another thread where someone had mentioned the nuetrall safety switch. Is this a waste of time or could it be involved in my problem?

Thanks

 

Just an update, checked for continuity in the wires that go into the VSS harness, no breaks in it from the VSS all the way to the ECU. Not sure where to find the neutral safety switch on this thing, or if it even would matter with my problem.

 

did a check of the DTC codes and I'm getting 16. I f I drive it for a while 24 comes up as well, wich from what I gather just means it's not getting information from the VSS.

Would DTC 16 have anything to do with a faulty VSS Buffer? Since I have the dash taken apart from checking the VSS wiring up to the ECM last night I figure I might as well go to a salvage yard and see if I can get a VSS Buffer to swap out before I go putting my dash back together.

Read up on the shift solenoids in the trans, but i didn't read anything about that casuing the speedometer to not work. Any input?

Before I go dropping the trans pan and testing out the solenoids I going to try the VSS Buffer. Maybe I should grab a couple from the salvage yard incase one of them is bad? Seems like the only place to get them new is Stealership, can't imagine they'd cost too much at the yard though.

 

Man symptoms like that would make me think its either the VSS, the harness, or the computer.

 

thank you for the input.

Since I replaced the VSS let's put that aside for now. I have continuity from the VSS harne all the way to the ECM so seems to me the harness should be good, I could be wrong though so feel free to speak up.

Now by "computer" do you mean the main ECM? hmmm

Yesterday I swapped the VSS buffer, no change.

I did come across a broken ground strap for the engine block though. I jumped the broken strap with a couple wires with clips, this didn't make any differance. Maybe my temp patch didn't give enough ground? Where can I get ground straps? would a parts store carry them? I couldn't find a listing online
for any local stores, I'll have to make some phonecalls I guess.

If the ground was broken could that have damaged the ECM messing up the trans function but leaving everthing else working? Is there a way to test the ECM besides swapping it?

Thanks again for any help

 

To test the ECM you would have to have a technicinan hook up a scanner to it. With that he can tell you everything that is wrong with it. They run around $75 to do that. Find a well known and good mechanic or technician. Some use those scanners and dont know what the heck some of the stuff on there means. This is gonna be your best option other than tryin to guess what will fix it.

 

OK, sorry to dig up an old thread but I'm still dealing with the problem from my first post. I know it's been a while but things have been really busy and this truck was purchased top be more of a toy and since it's not a DD right now it got pushed to the back burner.

Please bare with me as this is a bit of a read, but any help will be appreaciated.

So when I left off I was looking into the ECM/ECU.. whatever you want to call it.

We fixed the previously mentioned broken ground straps and just yesterday I got around to pulling the ECU, the harness that the pins for the harness that plugs into the right side of the computer (the blue one) were gunked up with what looked like vasaline so I was thinking I was onto something. Got ahold of a tested good computer with matching numbers from pretty much the same truck, swapped it in for the one I pulled out but still no fix to the problem.

So to recap- trans won't shift automatically. Moves in all gears (except P and N...of course) but in D stays in 1st, I can shift it from 1 up to 2 and it holds 2 with no slipping or grinding. Also speedometer does not work.

To date we have- replaced VSS, VSS Buffer, ECU, Ignition switch, I have traced all the wiring from the VSS harness up to the dash and behind the speedo and as far as I can tell the are no breaks or chafing anywhere and using a multimeter I can tell that current flows through the wiring so there should be no problem getting a signal from VSS to ECU.

Why haven't I taken it to a trans shop? well for one thing the nearest trans shop is further than I want to drive in 2nd gear and on an out of date state inspection tag, and I don't want to pay for a tow to a shop that's most likely going to try to get me to go for a rebuild wich I am not convinced it needs.

So to anyone who has sat through this whole posting a commend your patients and thank you for any input.

 

Yeah this really has to be an electrical bug. What Im thinkin is it is something unrelated to the problem. Like one GM car I had years back kept popping the fuse to the fuel pump. It started to do it every once in a while, then progressed to once a week, then it would just pop it all the time. It turned out to be the oil sending unit gone bad. Wierd!! I guess it was just a default for the computer to kill the engine sensing it had no oil pressure to prevent damage. Let me do some more research and I'll get back to u!!

 

Thanks, any input would be appreaciated.

 

well I finally got to the bottom of it. Ended up being the Brake fuse. I came across another thread involving a newer truck that had a lot of the same things I had going on and problems with ABS. even though I don't have ABS, I checked out my Brake fuse and found it missing, popped in a new one this afternoon and she shifts perfectly and speedo works again. Never would have figured the trans and speedo would be affected by that but there you go.


now hopefully the fuse wasn't missing because there's a problem that causes them to blow....fingers crossed.

looks like it's time to go tire shopping and get lifting this baby.