dlc1609

iTrader: (20)

Problem: Speedometer is not working after I installed a purchased PCM.

The seller of the PCM I purchased did not disclose what might be a HUGE problem.

Here's the scenario:
Recently, I killed my '98 M6 TA's computer doing a "write entire" while charging. I swapped in another '98 computer I bought from a tech member and now have no speedometer and reverse lockout is acting funny.

The guy I bought the PCM from said he had it on his M6 car and was told that is what it was (a '98 M6 computer) by who he bought it from. I did notice that all of the automatic transmission tables had data in them (which could be in all PCMs i suppose).

I originally copied all of my tune's info into this new PCM's factory file because I've heard you shouldn't use other PCM's files in some '98s. Everything was fine other than the speedo problem. I've since written my entire file from my old PCM into this new one and still having the same problem.

HP Tuners does not read any vehicle speed and I have thrown a code for speed sensor. (Can't remember the exact code because I cleared it and it hasn't come back)

1: Where should I start in trying to fix this problem?
2: Is it likely that the speed sensor just went caput during all the swapping?
3: If so, which sensor on the big T56 is the speed sensor?
4: I have also read that swapping between '98 auto and m6 PCMs can require a small wire change at the computer. Could this be my problem if in fact I have purchased a auto PCM and put it in my M6 car?

SOME OF THESE QUESTIONS CAN BE DISREGARDED AS IT APPEARS THE PCM MIGHT HAVE ALREADY HAD A PROBLEM. I AM STILL LOOKING FOR THE CAUSE OF THE PROBLEM THOUGH.

Any help diagnosing would be great!

dlc1609

iTrader: (20)

This is disturbing. A post by the guy that had the PCM before me:

https://ls1tech.com/forums/general-m...what-next.html

dlc1609

iTrader: (20)

And this:

https://ls1tech.com/forums/pcm-diagn...swap-help.html

dlc1609

iTrader: (20)

Here is where I bought it:

https://ls1tech.com/forums/texas-cla...condition.html

Seems like there was a problem with the PCM before I bought it and it was not disclosed.

If I can get the problem fixed, I don't care if the guy cheated me or not. If I can't, I'll obviously need him to take care of this by either refunding my money, or providing me with a good computer. The guy says he will chime in to clear this up.

98camaro28

iTrader: (21)

Allow me to shed some light here:

When my speedo stopped working, it was when I bottomed out my car that one night. The first thing I did was replace my vss. While I was replacing it, i put my finger in there to feel the wheel, and i did feel it. So I figured I might have cut/pinched a wire somewhere due to my car scraping on the ground. Just to be sure, I re-wired the ENTIRE thing. Didn't help. So by now Im thinking that is IS the PCM. So if I was going to be buying a new PCM, I was going to be doing the swap for better tunability AND to hopefully resolve my knock sensor problem. Well, I did the swap and BOTH problems still existed. So finally I got my hands on a scope and pinned the output of the VSS at the PCM to see if it was getting anything... and it WASN'T. SO I took my car to Performance Transmissions in Kennedale, and they pulled the tranny out and sure enough, the wheel was cracked andwas sliding down the shaft. (Which I was told is VERY rare, hence all my threads with an issue on this problem.) So with that replaced, I FINALLY had a speedo! And since I know it wasn't the PCM, I sold my 98 computer. When I sold it, I even said "There will be a code for the VSS due to the reluctor wheel being all f***** up, and false knock, but other than that it is perfectly fine." and he said something along the lines of hating the knock issue with the 98s, and that he would just load his tune on there. So, bottoming out wouldn't make much sense in making the PCM go out. But it could be linked to my reluctor wheel. And since the speedo issue was intermittent, due to the wheel moving around, that also points away from it being a PCM issue since a PCM issue would, I'm assuming, be a permanent issue. So just to clear this up, I have a decent amount of positive transactions on here and NOTHING negative. I am on here EVERY SINGLE DAY and would have no reason in the first place to sell somebody a PCM that didn't work.

OP, I'm sorry you're having issues. This is probably just all a freak coincidence somehow. Please let me know if I can help you track down the problem.

98camaro28

iTrader: (21)

Also, my car is an M6 and that was, to my knowledge, the original PCM. (I bought the car with 60K on it.) The speedo worked flawlessly for thousands upon thousands of miles. So it can't be an A4 PCM.

dlc1609

iTrader: (20)

I too am on here EVERY SINGLE DAY and have much + feedback myself. I haven't been able to determine the problem yet but when things become this coincidental i become leery... Like I said by text, I'd like to believe that there is no problem with the PCM. Maybe someone will chime in and help me determine the cause....

Frost

iTrader: (45)

If you have seen this code even once, I'm not sure how we could think it's the PCM... Why not start with the source of the code. To be honest, in well over a thousand PCMs, the only one I have ever seen go bad wasn't really 'bad', but the IAC's driver output was dead.

It's programming shouldn't be an issue since you would have flashed the new PCM (write entire) with your old file.

I would have a close look at the entire VSS circuit from PCM to the sensor and back. Set your VSS errors to all report on first event in the DTC setup.

dlc1609

iTrader: (20)

Thanks for the reply Frost.

I'll actually be thrilled to find a problem other than the PCM. With you not ever having seen a PCM with a problem like this, I'm sure I will find the cause elsewhere.

I'm going to change that DTC setup stuff and see what starts popping up. Sounds like it is all just a "freak coincidence" like 98camaro28 said.

Frost

iTrader: (45)

If you set them all to error on first, one should show it's head. Leave the SES enabled box checked so that you get a dash board reminder.

dlc1609

iTrader: (20)

I did just that and it worked. Took 'er for a spin and about 5min in I got a P0500 Vehicle Speed Sensor (VSS) Circuit code. About to use the wonderful search feature on this site and see what type of common problems might cause this code....

edwardzracing

iTrader: (59)

So I'm assuming there were no speedo issues prior to the PCM swap, yes? Writing to the PCM while charging, hell doing anything while charging can be a risky little game, so who knows? Perhaps that had something to do with the VSS as well as the PCM. Is a speed sensor expensive? Why not try replacing that and see what happens?? Keep us posted on what you find out and what the fix is (hoping you find one). I like when a troubleshooting thread ends with a positive result. Good luck.

dlc1609

iTrader: (20)

You are correct. Had no VSS problems prior to the swap, which is why I was suspicious of the seller when he had the same problems on his car. I had figured maybe that particular circuit in the PCM had a problem, but since Frost has never seen that, it is doubtful that is the case...

I don't think speed sensors are expensive (maybe $25) so I'll pick one up tomorrow and see if that helps.

Frost

iTrader: (45)

It's not the fact that I haven't seen it that makes it doubtful, it was that it had previously coded.

dlc1609

iTrader: (20)

To be clear, the old PCM had never had this issue nor thrown a code for VSS. Ive only had a VSS code thrown with the new computer.

And I'd say with all of your experience in with these, if you haven't seen it, it does indeed make it doubtful...

dlc1609

iTrader: (20)

Update:

Just replaced speed sensor on transmission and it was no help. Speedo is still registering nothing, my reverse lockout is still acting up, and it seems easy to miss 5th (it grinds, feels like there is no positive stop on the right hand side of the 5th gear slot). All of these problems are new as of the pcm swap.

Again, it is so weird that I'm experiencing the same problems the previous owner had... It just doesn't make sense....

Where do I look now? Is there a way to test vss voltage or something at the computer?

dlc1609

iTrader: (20)

Tried disconnecting computer and hooking it back up. Nothing. Any ideas from anyone would be appreciated...

98camaro28

iTrader: (21)

Get a scope and pin the output wire of the vss at the PCM to see if it is getting signal.

dlc1609

iTrader: (20)

What do you mean by scope? Multimeter? What do I check? How do I check it, while wheels are spinning? What am I looking for?

98camaro28

iTrader: (21)

Its a tool that will see the "wave" patter of the VSS reading off the reluctor wheel in the tranny. The faster the wheels are spinning, the higher the frequency. Im pretty sure the VSS output is a green wire, but I can't remember what exact pin it is. Im sure somebody here can go into better detail, but its pretty simple.