StewsRunner

iTrader: (1)

Hey guys, recently my speedometer and odometer went out with the occasional CEL and flashing O/D light. I pulled code 42 which is leading towards the speed sensor. I have seen a couple threads on here about it and looked into it. The threads I found were mostly fixed by replacing the speed sensor and thanks to Scope for providing a picture for me, it looks like it is right next to the drive train going to the rear. I also confirmed that with this picture taken by Robin Hood,



The top picture is the one that scope provided for me and it says it's for an A340H auto tranny which is what I have. I got down under my truck and snapped a pic of mine. Mine however does not have the sensor, only a cable coming out and going up towards the fire wall, to the dash i'm assuming.




I have read that the speed sensor was from 92-95 which is electrical. Mine is a 91 so Does that mean mine is mechanical? My info may be wrong but does that mean that I just need to examine that cable?

I also some how got directed to Marlin's speed sensor where it says it's for 92-95 only?

MudHippy

What you have is an electrical VSS in the speedometer assembly instead. It's driven by the cable from the rear of the transfer case. It's what's refered to as a Reed Switch Type. The other type of VSS is a MRE(Magnetic Resistance Element) Type.

See page 6 & 7 here for more info on VSS types.

There is no specific way to test the VSS. Well there kind of is, just not testing it beyond to see if it works at all. Which you can do. But to fix a code 42 means usually fixing the wiring between the VSS and the ECU. Because the sensor itself will rarely ever fail, and as such, will rarely ever fail if tested. IMO, it's pretty much a given that it's not really the problem. But if the rest of the VSS circuit checks out, and/or the VSS appears to not be working/malfuntioning/damaged, then you could try replacing it. Which means replacing the enitre speedometer assembly(speedometer + odometer + VSS). And it ain't cheap($125+). But it would be cheaper than replacing the ECU, which would be the only other thing that could be causing it.

Here's some pics of mine(88 3VZ-E) for reference.

Back of the combination meter.


Speedometer assembly.


The VSS terminals close up.


VSS reed switch closer up.

StewsRunner

iTrader: (1)

Alright so you are basically saying that I have a VSS but it's attached to the Odometer and not the tranny.

In your first pic, the hole behind the Odo, is that where the cable from the tranny comes too? I found it behind my gas/brake pedal connected with the E brake. Is that what, in a sense, turns the speedo and odo?

In the pics of the VSS, I see what looks like a broken/burnt fuse? Is that correct? Now on mine, will I find cables coming off of the two prongs going to the ECU? Is what you are syaing I should look into first?

Is there no way I could take the VSS off and replace it with a junk yard one or would I have to pull the whole unit out of a junkyard car?

Here is the cable i'm looking at, is this the one? I guess it doesn't really matter if the wires between the VSS and ECU are likely the culprit

MudHippy

The cable turns the speedo + odo + VSS. If the cable is broke then the speedometer and odometer don't work either. The rest is exactly as I explained and/or as the pictures clearly show. Or you can see the link again on pages 6 & 7, http://autoshop101.com/forms/h36.pdf for the illustration and explanation of how a Reed Switch Type VSS is constructed and functions.

Good luck at a junkyard. But anyway, without knowing for certain what the problem is with the VSS, you need to replace the entire speedometer assembly as a unit. Because the problem can also be with the parts that aren't shown in the pics(but are illustrated in the link above, which you didn't read carefully enough...if at all). And even if you could somehow test the reed switch and find it to be bad, you still don't know if the internal parts are good. So replacing the reed switch wouldn't necessarily solve the issue with the VSS.

The speedometer drive cable for the 3VZ-E shown at the bottom:

StewsRunner

iTrader: (1)

Okay I gotcha, yea I didn't go to in depth reading about the Reed Switch Type but I understand what you are saying by the inner parts could go bad. I also pulled out my cluster and got a better look at everything and how the VSS hooks up the "mother board."

you say $125 +, are you talking from the dealer, a part out or a junkyard. You say good luck at a junk yard and I don't mean to be a smart @$$ but do you mean I am only going to find a crap one or not one at all?

i appreciate the help man and after looking at everything, it looks pretty straight forward. Replacing the Speedo unit seems easy enough and the cable, if it comes to it, seems like a time worthy task but do able.

It seems like the hardest part now is waiting for my pay check haha. So I will go ahead and do my best at a junkyard to get the Speedometer and possibly the cable, hopefully for cheap just too see which one is the issue. If it's one of those then i'll go ahead and possibly buy brand new.

MudHippy

Well, you might find one at a junkyard. Or they might try selling you the whole combination meter. Some speedometer assemblies are more rare than others, and there's 16 different kinds for a 91(including 8 for kilometers and KPH). Just good luck really, not sarcasticly. Meaning I hope you find the right one, and that it works.

StewsRunner

iTrader: (1)

So I was about to head to a junkyard to pick a tach up when I remembered some advise SuperBleeder gave me. He insisted I pull out the tach and drive around the block to watch the needle coming out of the cable. He said when his sppedo went out the needle was spinning but my needle is NOT spinning so it that a sign my cable is no good or the piece in my tranny is no good? I think I might head down there anyhow and pick up both, just for good measure in the future.