Lorenfb

"I've seen several CPU's used in the CCU, mostly Siemens 80C515/80C535."

Your info indicates basic 805X NMOS 8 bit microcontrollers updated to a CMOS
process with A/D with & without mask ROM. Since my Intel data books are
lacking, assuming 16 bit on my part was incorrect and would have been
an over-kill. Intel licensed Siemens to produce some of its UPs to have
a European second source. So if I had researched longer I would have
found the Intel 80C51 with A/D requiring a 68 pin PLCC. The 80C535 requires
external memory (1st image) versus the 80C515 which has mask ROM.
The images show the serial EEPROM (fault code memory) in the upper right
corner, i.e. the 8 pin mini dip. Most likely the 80C535 was used in the early
production (Euro cars) to shake-out/verify the firmware.

Thanks for your clarification Tore.

mnpopi

I am the customer Lorenfb refers to, and am happy to report that his mods to a 993 CCU work perfectly in my 964, and I have a fully functional CCU after almost a year trying!

Also, thanks to Tore for helping me with diagnosis!

Lorenfb

"I have a fully functional CCU after almost a year trying!"

Read here under 'CCU 964/993' for info:
http://www.systemsc.com/problems.htm

x98boardwell

So, I have a '91 C4 with an early style 993 CCU (from PO) and the G1 & G19 are not crossed.

I have been having some issues with my A/C not working and have verified all the other components are functioning and think that the G1-G19 may be the issue if it's putting my system in fail safe mode. I had 9 faults when I took it to the dealer to have them read the OBD1 port. After them being reset it didn't change the function at all.

Do I just bridge these two wires (G1 & G19) together and then plug it back in to the CCU?

Thanks,
Bryan

ToreB

Hi Bryan, bridging G1 and 19 is only one of several needed modifications to make a 993 CCU work in a 964. There's others too, depending on the CCU (993 donor) model. 993 CCU expect two rear fan feedback signals, and therefore the bridging is necessary.

Deleting fault codes in the CCU will not affect its operation. If you inform of which faults that were stored, or what is your problem in the car, I might be able to help you in this.
Cheers,
Tore

x98boardwell

CCU is the older 993 variety so we're good there. I am having some rear fan codes that went. Looking to confirm now and I will repost.

I was able to find a donor 964 unit to see if it works in my car so that should be here by the weekend. Will let you know on codes asap. I know rear fan and rear fan stage II was a couple of them. Who knows how long they've been in there. I did see that G1 & G19 we're not crossed. My guess is that the PO didn't know or the indy that put it in didn't know since it all connected fine.

Thanks for sharing some wisdom.. In my search over the past few weeks I have seen this thread many times and finally after coming to dead ends I figured I would just add a post.

Cheers,
Bryan

RT930turbo

Major thread revival...but I wanted to share the above information allowed me to put a late 993 CCU into a '90 C4. The climate control was completely unusable until I made the G7 and G9 changes. Everything now functions perfectly. Interestingly, I hooked it all up prior to making the G1 and G19 bridge, and it seems fine. I'm going to install the jumper anyway to make sure it doesnt behave odd when the weather gets cold.

joe1boss

Hi,

After cutting the G7 and G9 what end of the wire you cut was grounded and the resistor added to ?



Thanks Joe