Rob Edwards

Weirdly enough, it didn't. It was fine for about a month, then got the error message again driving around Wednesday night, speedo is dead again. Weird.

SeanR

You can also have an issue with the inertia box under the drivers seat. It's a small unit, and often over looked.

The internal connectors in it can get corroded, and not give the proper signals to the controllers. The fix is to pull it, clean the internals and reinstall. Trust me, the controller is expensive, it's best to take it apart and look at it. Had one customer that we played with it and I gave him the option of replacing or me dicking with it. He wanted to know the price and it was high, so he pulled it, cleaned it after telling me it looked good. Told him to dig deeper.

Saved him $400. I think the proper name is the accelerometer.

Rob Edwards

Sean-

Cool, good to know. I will pull the seat and have a look. Sucks not having a speedometer. 'No Officer, I have no idea how fast I was going....'

RKD in OKC

Wow, my 94 GTS started having this problem exactly, ie., Diff controller OFF, ABS OFF, and no speedo. After reading this I realize it happened after moving the driver's seat back, then forward before making an autocross run where the lights started coming on. I move the seat back, lock the cam on the seat belt the move the seat forward to tighten the belt enough to keep the cam locked. I'm betting moving the seat did something to the wiring of the inertial controller box.

By the way, autocrossing SUCKED without PSD. I can handle the braking fine without ABS, but with one tire trying to put down power I was 6 seconds slower compared to my usual competition for FTD.

Rob Edwards

Jiminy Christmas, hope I don't need a new one:

http://www.pelicanparts.com/cgi-bin/...ACCEL%20SENSOR


EDIT: Sean- by internal connectors, do you mean the recessed 3 pin connector terminals, or actually inside the unit? The unit doesn't seem to want to come apart non-destructively.....

jeff spahn

Wowzers. $2500 for the sensor. I'll make sure I don't touch that.

cold_beer839

My GTS has done 3 times in a row recently, but not the last time I drove it. The "ABS OFF / Differential Control OFF " warning and ABS light turn back off after it has been driven anywhere from 1 foot to 1/8 mile. I think I need to clean the ABS sensors.

$2500 for that sensor is about like getting hit over the head with a lead pipe and your wallet taken....

928GTSM

I had this exact same problem on my 93 GTS recently and the same as a previous poster I replaced the ABS relay at the suggestion of John Speake and so far touch wood the problem hasn't re-appeared.

Rob Edwards

Well, it's certainly easier to swap the ABS relay (928.615.124.01) out of my GT than it is to pull the driver's seat. Thanks for the test suggestion!

SeanR

You can remove the sensor w/o pulling the seat, just move it all the way forward. It should be under a piece of blue protective tape.

You can pull the sensor apart, just be careful doing so. It's plastic. There are electrical contacts that can get corroded up, or have metal flakes keeping the sensor from working properly.

If you do a search for 'accelerometer' in the 964 section, there are a lot of write ups of people doing it, but no one bothered to put up any pictures. I don't have one handy or I'd do it.

Rob Edwards

Update:

Swapped the ABS relay from the GT into the GTS, speedo is still dead. So it's not the ABS relay.

So I'm a dumbass. I remember finding this rectangular piece of plastic under the driver's seat after reinstalling the refinished seats. I must have knocked the cover off the accelerometer during reassembly. I put it in the used parts bin but didn't actually check under the seat until tonight.

D'oh:



So the accelerometer has been uncovered for a month or so. I pulled it out of the car (put the seat all the way up and forward before disconnecting the battery, then 2 philips head screws and a 3-pin connector and it's out.) and flushed it with CRC contact cleaner and put the top back on. Reinstalled and went for a loop around the block. Speedo is still dead.


I picked up a pair of used lateral accelerometers to try today:



Swapped one of the spares in, went for a drive, still no speedo. So I guess that it's not the accelerometer itself, which is a good thing, relatively speaking.....

Now I'm not sure what else could be FUBAR if it's not the ABS relay, the front left ABS sensor, the lateral accelerometer, schmutz in the ABS sensor wheels, or ??????

I didn't see any metal filings or any gunk inside my accelerometer, but didn't try to extract the circuit board held in with the Torx screws. Sean, should I have pulled it out and looked at the underside of the board?

Guts:

RKD in OKC

Woo hoo!!!!

Mine was just a plug that had come unplugged under the kick panel.

SeanR

Rob, yes, pull the circuit board out, that is where the gunk gets stuck. I don't think this is going to fix the speedo, but should help with the PSD/Diff control off.

Also, how are your barrel connectors on the pass engine compartment? Is the ground still attached?

Rob Edwards

Kick panel? Under the left foot rest? Up by the hood release? Elsewhere? I'm still grasping at straws on mine. (Below)


I pulled the LF wheelwell apart last night - the ABS unit and the relays on it look fine



BUT- there’s a section of the ABS wiring harness just aft of the shock where it looks like someone cut into it at some point (it’s wrapped with some cloth tape).



I pulled off this section and there are all these splices in the wiring, though they all appear to be intact. Do these splices look factory to you guys, or hacked post-factory?

I guess I should actually read the WSM section on ABS....

Rob Edwards

Next question:

All the WSM pages, tech bulletins and InfoTechnik manuals pertaining to testing ABS systems reference the 35 pin ABS brain connector. I can't find any info on the pinout of the 55 pin connector used starting on 1990 models. There's a pic of the pinouts for the 964 PDAS/ABS 55 pin connector on page D39/45-7 of volume 4 of the 964 WSM, but somehow I doubt it's the same as the 928 connector.

Anyone got the lowdown so I can check resistance of the ABS sensors at the ABS brain connector? Or did I just miss the info and it's somewhere on my hard drive already?


EDIT: Sean- missed your post earlier today, sorry! I'll pull the circuit board from the accelerometer and clean it again, and see if that helps.





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