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2K views 21 replies 4 participants last post by  pabuckrub 
#1 ·
I just picked up an 88 Seville in MINT condition. I keep getting the code for the vehicle speed sensor and the spedometer doesn't work along with some other electronic stuff that is thrown off by not having a VSS signal.

The digital dash seems to be OK and everything works on it along with the DIC and Climate controls.

I took a look at the sensor and someone had the wires unplugged so I plugged them back in and took her for a ride. The spedometer started jumping around and then went to 85 and started flashing and then THE CAR SHUT OFF. I didn't even get a block from my garage. I restarted it and got it back to the house and proceeded to remove the sensor. When I got the thing off, all it appears to be is a gear driven shaft, nylon on bottom and metal on top that passes in front of some sort of magnetic pickup. Everything seems to LOOK OK so I put it back together and plugged it back in and took it for a ride... same thing happened. So, I just unplugged the wires again so that I can drive the car. It runs OK but doesn't shift quite right and obviously no speed reading on the dash... stays at 0. But at least I can drive it.

I can't think of anything else that could be wrong so I ordered the part (VSS)from cadillac parts dealer.com at a hefty cost of one hunderd and thirty something, normal price being $167. The local dealer told me $167 also.

I was wondering if anyone else ever replaced one of these and what the cost was and if the problem was sloved by replacing the sensor. Like I said, there doesn't seem to be too much to it to go bad. Comments appreciated.

Thanks.
 
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#2 ·
The car shut off? Must have been reporting something cool like 300 mph, or anything above fuel cut for that matter. If you can unplug the sensor, and it works fine, then you have pretty much eliminated wiring as a suspect.
 
#4 ·
I would imagine so. when it flashes 85, thats the upper limit the speedometer on that year displays. check the nylon parts, see if there chewed up at all.
 
#6 ·
I do agree, failure mode is awfully odd, don't they normally just go open when they fail, like most coils? The odd part is that it is isolated to the sensor. If there is AC feedback from the alt. through the harness wouldn't that show up regardless of it being plugged in? Is there any shielding on the sensor that may be damaged, maybe a ground strap? :hmm:
 
#8 ·
Anyone know where I can locate the VSS on my Seville, 1988. I called to ask about the part because it didn't look close to the part that I had off and they parts guy, after faxing me an exploded picture, said that the part I described was the "governor", so I put that back on and can't find the VSS. For some reason, the people that I bought the car from had the "governor" unplugged. When I plugged it back in the car went wacko flashing 85 on the spedo and then shut off. Is it possible that you need a good VSS to have the governor plugged in? This is starting to get out of hand. A part that I could fit in the palm of my hand and I can't figure out where it goes. From looking at the diagram that was faxed to me it looks like the VSS is with the engine? I thought this was attached to the transmission somewhere. HELP PLEASE.
 
#10 ·
This is the first place that I looked and the only thing that is there with any wires coming out of it is what they are calling the governor, which is a lot bigger than the new part that was sent to me that they insist is correct. In the above picture it looks like the VSS goes into the transmission horizontally. The governor that is in my transmission operates on a vertical shaft. I had an AAMCO employee tell me that the speedometer is controled by what they are refferring to as the governor, but I don't know if I believe him or not. I guess what it comes down to is... are these two separate items that we are talking about here? This picture only shows one yet the exploded view that was faxed to me shows a separate part (VSS) that is held in by a retaining clip. The governor housing on my transmission is held on by two 13mm bolts and the shaft just kind of sits inside of there. I'm still not getting it. Anyone have the shop manual for an 88 seville that could scan me the complete pages along with what the numbers identify, or the text for replacing the VSS. The directions I got with the part said refer to shop manual. I only got a few pictures with a bunch of numbers by a bunch of parts and that doesn't tell me anything. I looked on-line for shop manuals and found them for $150. I don't really want to pay big bucks for something I am only probably going to use once unless I absolutely have to.

Thanks for all the help so far.
 
#11 ·
Ok, here's the deal. The jackass (can I say jackass?) at the Cadillac dealership that I got the new part from went on and on with me that the one that they sent me was the ONLY one listed for my car. Again, it looked NOTHING like the part that I believed to be the VSS.

So... I've been asking around about this quite a bit and getting the same story from everyone that I talked to. IT'S THE WRONG PART. I called the dealership back at least three times and kept getting the same answer from them... it has to be the right part they say.

Yesterday, I went down to the local NAPA store for a thermostat because mine was obviously not closing and was shot. I asked the clerk, just for shits and grins, if he had a VSS listed for my car. Low and behold he said that there are TWO listed... YES TWO. I asked him if he had a picture of them and amazingly, in the catalog, he did. One was the one that the dealer sent me, and the other looked exactly like what was on my transmission... SO, I ordered it... $78. I came home and called the dealer that sent me the wrong part (from out of state... I got it on the Internet) and after an intense battle was able to convince them to allow me to send back the wrong part and get my money back. I had to threaten to call General Motors and complain first.

I thought for sure that this part would have to come from the dealer so I never bothered to check the local parts store. The moral of the story is, never underestimate NAPA because they have their stuff together.

It is supposed to be in today and I'm going to put in on today. The real question is this: What if the car still acts up after I put the new part on? What do I replace next?
 
#12 ·
I replaced the sensor and it still does the same thing. The speedometer starts jumping all over the place as soon as the vehicle is moved and then starts flashing 85, then the car shuts off.

Where do I look next?

What is the VSS connected to?

I would think that it has to be somewhere in between the sensor and the display????

Advise please.

If anyone knows the computer component that the VSS is connected to, let me know where it is located and what it looks like. I can probably get one at the junk yard.

THANKS!
 
#13 ·
Here's the latest update. I just replaced the ECM and the car does the same thing when I plug in the VSS. Now we have a new VSS and a new ECM. Here's the twist... when I had the dash apart to put in the new ECM, I noticed that someone replaced the BCM with one out of an 86 Buick Rivera (it still has the tag on it). Does the VSS in any way interact with the BCM? When I go through the BCM inputs on the DIC, there is a speed display.

I have a shop manual on the way but didn't get it yet. Any suggestions?

From what I can tell, that's the only thing it could be. Where do I find the right BCM for an 88 Seville???
 
#14 ·
Are you sure it is set completely into the trans?

I guess you could have someone sit in the car and you spin it in your hand (probably dont want it to make complete contact with the magnets... Mine seems like it could be plugged in wrong possibly...

If none of the above id take the one you bought back ASAP to get your money back.

Do you have the round aluminum one or the one with a black plastic ribbed back on it? My '88 has the round one and my 89 has the black plastic one...

If you need a BCM id look for one on ebay or www.car-parts.com

ebay also has factory cadillac service manuals for about 20 bucks...

I would go into the diagnostics and watch the signal from the VSS (look at the sticky in the 4.x forum), possibly your '86 BCM needs the aluminum round one (I think thats the older style)...

Id still be warely of the '86 BCM, but then again if they swapped the proms then It would possibly be ok...

Regards,
Brian
 
#15 ·
What do you mean by prom? Is that the little memory stick like the one that I swapped out of the old ECM into the new one?

The VSS that is on this car is the aluminum top held in by two horizontal 13mm bolts. The dealer originally gave me the other (plastic top) one that you described and I returned it and got the right one and replaced it, so that's new.

The only thing left to replace is the BCM. I wonder if whoever put the one from the Buick Rivera in, that's in there now, swapped the PROM. If not, I guess that would cause a whole bunch of problems. I am going to look for a BCM out of the exact same 88 caddy seville, with the same speed sensor at the junk yard first (if I can find one there).

I can't think of anything else that it might be?
 
#16 ·
Exactly, its the little memory chip under the screwed on plate.

www.car-parts.com shows that an 86 riviera will swap with an 88 seville, but your right if the person who did it first didnt swap the prom you might be in trouble, but hopefully they did.

You also have to make sure there isnt a problem with grounding or your electrical connections. Before you buy a new BCM Id check out the factory cadillac (not haynes,etc) service manual, it has a whole testing procedure to back track problems to the source. It could be that your UART data line is loose somewhere, or is bad going into the BCM... there is actually at least a good 1/2 dozen "It could be..."

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=10773&item=7112588036&rd=1

I think there were changes electrically between 88 and 89 so stick with an 88 manual.

Good luck,
Brian
 
#17 ·
Here's another good question... Does anybody know if I can change any settings in either of the two (ECM and BCM) computers through the dash? Being that my BCM is out of a Buick Rivera, that might be what the problem is in how the computers are reading the data from the VSS. I am thinking that the VSS from the other car was probably different and is conflicting with the BCM with it's current settings. I thought I remember seeing something that can be changed via the dash controls. There was a bulliten that said something about bypassing something to remove the electronic shock absorbers being replaced with non-electronic. What do you all think about this? I am still waiting for my factory service manual before I can explore this any further.
 
#18 ·
But mind you the buick riveria has the same transmission as yours (slightly different mechanically inside), so the VSS should be the same. But I am not sure how far back the black plastic incased VSS was used, I know my '88 eldo had the aluminum one and my 89 has the black plastic one, and there is a note in my 89 factory service manual that transmissions came with either one in 89.

Your on the right track by getting that manual, it will help out a lot.

-Brian
 
#19 ·
Here is some advice on how to watch your VSS signal to the BCM or ECM... Your manual will show where exactly in one of the connectors to put a digital multimeter...

Regards,
Brian


> 94 Ford Conversion Van with a 5.8L engine and E4OD trans.
> intermittent shifting problem
> While driving in 4th gear at 50 mph, vehicle appeared to neutral out.
> Snap-on scanner ... computer commanded 2nd
> vehicle speed changed from 50 to 12 mph on scanner but still 50
> on speedometer.

> changed the speed sensors in the trans and diff.
> This did not solve the problem. also changed MLPS
> gone over the wiring to check for corrosion or a bad
> connection. Has anyone seen anything like this?

You kidding? lol its a ford! nothing new. anyway...
You did not mention if MLP volts dropped at the same
time it downshifted. If MLP volts are steady as a rock
when viewing a MOVIE frame to frame, mlp is fine.. not the cause.
If speedo reading is irratic yet speedo reads fine, don't believe
the speedo.
Did u ever do any boating? or play with a wave runner?
you can hop wave to wave on the tops without riding down
in the dips. a speedo can do the same thing. The mechanism
on the dash (especially needle type) can't react fast enuf to
display irratic/fluctuating signal.. just like an analog meter
can't, but a digital will have the numbers scrolling all over
the place.
now, please don't misunderstand..
I'm not suggesting you don't know how to test wiring..
I just wanna make sure you checked it thoroughly..
if it were me, i'd put the digital meter on the speed sensor
wires AT THE ECM, and set it to OHMS.. and go
for a ride.. watch for numbers to go berzerk when you
hit bumps and stuff (kinda like an in-car wiggle test).
ohm'ing the harness on the rack is one thing, but
bouncing around is another. either roatest-ohm it, or
get your installer to start gently pulling the wires around
while u watch the meter.
connectors are notorious for that kinda behavior
HOT with VIBRATION

by the way.. when i see a bad ohm-roadtest, i just
patch in new wires.. forget that crap of trying to find
the bad spot. its a waste of time. i keep a couple rolls
of 16 and 18 guage wire and just piggy back/scotch lock
new lines in and be done with it in quick fashion.

Best wishes..
Dean

ps.. if u do see crazy intermittent readings but are certain
your wires are good, you might try holding 2 or 3 clicker
type pens in 1 hand and click them simultaneously on the
chasis of the ECM to see if small vibration directly on the
outside can induce goofy reading while you run it at steady
50mph cruise on the rack .

this is a well known Ford click test.. commonly done with
1 pen directly on a sensor. the click of the pen sends a
nice tell-tale jolt thru the sensor.
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#20 ·
It appears that I was correct in my guess. The VSS goes into the BCM which converts 4000 pulses/minute to 2000 or something like that and then sends it to the ECM. Very interesting... this means that I have a bad BCM since I already replaced everything else.

The factory service manual is very complete having flow chart type trouble shooting for every component in the car.

Now that I know the VSS involves both modules, I pretty much don't even have to do the tests and know what the problem is.

All I have to do is find a good BCM and I should be in business. A new one is only about $150 on the internet so I think I am going to go that route since everything else is new. I don't want to take the chance on one from a junkyard. It appears that is the problem that the last owner had.
 
#21 ·
pabuckrub said:
It appears that I was correct in my guess. The VSS goes into the BCM which converts 4000 pulses/minute to 2000 or something like that and then sends it to the ECM. Very interesting... this means that I have a bad BCM since I already replaced everything else.

The factory service manual is very complete having flow chart type trouble shooting for every component in the car.

Now that I know the VSS involves both modules, I pretty much don't even have to do the tests and know what the problem is.

All I have to do is find a good BCM and I should be in business. A new one is only about $150 on the internet so I think I am going to go that route since everything else is new. I don't want to take the chance on one from a junkyard. It appears that is the problem that the last owner had.

I'd still do the tests... It shouldnt take too long since you already have the dash loose/off...

If its your BCM then Id go to carquest and try and talk to them. Im not sure if they can check it in house or if they have to out source it (which would mean it would cost money to just check it) But they should at least have some kind of table of prom id's to check and see if yours is the correct one.... For $150 id make sure its a certified OEM GM/delco part. I sold an '88 eldorado BCM once for $30 or so bucks on ebay to some guy in russia... But make sure the one you get has the correct prom in it, should have to give the company all of your options off of your build sheet (found mine in the trunklid's recess, next to the lock).

Good luck,
Brian
 
#22 ·
OK, I finally got it all straitened out. Here's the deal. There was nothing wrong with the VSS itself, or the ECM and it's PROM. I replaced both. Then I got to the BCM. It appears that this year had two different BCM's depending on which VSS was used, there were two different ones in this model year. Amazing that the only ones who could tell me that was NAPA parts store. The cadillac dealer insisted that he sent me the only part listed for my car... he was WRONG so beware of this as GM dealers don't have this information. I have the VSS with the metal "cap" held down by two bolts. The other is held in place by a clip and has a plastic top. I went and got quite a few different BCM's (same year cars) at the junk yard and tried them all... seven bucks a piece. I finally tried the one that I marked as having the same VSS as my car and EVERYTHING worked. The PROM that was in the BCM that came with the car, marked Buick Riviera, was the original PROM. I found that out by displaying the VIN number on the DIC, which matched the car.

SUCCESS! I have a brand new (old) 88 cadillac seville with 98 thousand original miles in mint condition. Thanks for all your help.
 
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