(Only for a 95 993 6 speed)
Caution: When handling electronic components please observe the proper anti static rules, wearing a latex rubber glove will be the least you can do.
Once the front bolts have been removed, move the seats forward to reveal the 4 rear mounting bolts. It would be safer to use a hex socket to remove these bolts instead of using a allen key, you would have a higher chance of stripping the bolts with an allen key.
Some said it is not necessary to take the seat off to get to the OBC, but since I am installing a 5 point harness next the seat had to come off any ways.
Turn the OBC upside down and pry up the tabs that secure the cover in place.
Turn the OBC around and remove the cover, and locate the EPROM chip. Remove the plastic cover on the top of the EPROM chip by inserting a flat screw driver in the slot on the side.
Using a flat screw driver carefully pry up the EPROM chip, at this time please carefully note the half circle slot on the top of the chip, the new chip will need to go back in the same direction. Here is a picture of an old and new chip.
Reinstall the cover, bend back the metal tabs on the cover. Install the OBC mounting bolts and the wiring harness, and you are done.
Todd Campbell made the below contribution after his experience to replace the PROM chip in his 95 993 Tiptronic, the difference here being that his car is equipped with a Tiptronic transimission.
This is what is listed on your site regarding Chip replacement for a 95 993:
“Some people have
said it is not necessary to take the seat off to get to the OBC, but since
I am installing a 5 point
Well, in my case, a 95 993 with Tiptronic transmission, after I removed the seat, I was presented with an aluminum shroud that covers all of the wiring harness for the DME and is held one with 4 security bolts. (Also note that my DME is actually mounted facing the opposite direction than the picture on your site indicates. My wiring connector is also relocated) These also hold down the DME and the Tiptronic computer (also in this area is the alarm brain—referred to elsewhere as the immobilizer). The only way I could get the DME out was to drill out the four security bolts. While this poses a challenge somewhat due to location it also makes an incredible mess under the computer wiring. If I were to do it again, I would use a vacuum cleaner while I drilled the security bolts. This would at least help with the metal shavings. I would also need a third hand—or a helper.
Anyway, the security bolts are threaded in (not riveted) and this may make it easier to ultimately remove the shroud (i.e. by finding a method to create a head that would take a flat head screwdriver for example). I ended up removing the pan that the DME, alarm and Tip computers are on and cleaning out underneath the area. I also then removed the remnants of the security bolts and replaced these with standard 6 mm x 30 bolts and washers, and reinstalled the pan, computers and ultimately reinstalled the shroud to keep it factory.
Attached are some images that show the shroud.