Problem: The odometer stops at 299960.
Models: All models manufactured before 2/89. You can check if your car will be affected by holding the trip reset button while turning the key from I to II. If the cluster preforms a self test your safe. If it displays a code number keep reading !
Background:
The milage and car specific information are stored in a chip in the back of the instument cluster called the codeplug. On early clusters, the ones from before 2/89, it's a blackbox in a brownplug that plugs into the instrument cluster. Later types have the chip intergrated in the backplate of the instrumentcluster.
There are 3 chips used as codeplug in the E32/E34. In order of production these are: HML075, PIC 93C46, PIC 93C56. The HML075 chip is the affected one. I couldn't find anything about the manufacterer of this chip or a programer to read/write from/to the chip. The last two are standard serial EPROMS and can be reprogrammed by anyone with an EPROM programer. Kind scary isn't it ?
There is no clear reason for me at this time why the counter stops. The chip's internal representation is 40km higher making it 300000, which still doesn't give any clue as to why it stops.
Solutions:
Live with it
This is by far the cheapest option.
Buy a new codeplug
We all know the dealer hasn't got enough money already. So if you bring him Eur 110 he will get you a new code plug. The new plug starts counting from 0 and will display a red led next to the km symbol to indicate that the codepug has been replaced.
To order the new plug you will need your VIN and your original codeplug number. The number can be read from the codeplug itself or can be obtained by pressing the trip reset button on the instrument cluster while turning the key from off to the accessory position.
Offcourse you can also get a used codeplug for Eur 20 to 50. Be sure to get one with the right number on it. If you don't you may be lucky enough to get everything working if not you might end up with incorrect information from the OBC and the cluster.
Have the plug reset to 0
There is a wide variety of conmen and official VDO repairshops that claim they can do this. My experiance is that they can't do it themselves and have to send it out. I had to wait 10 weeks to get mine back. After doing without all features of my instrument cluster execpt for the speedo and the rev counter I was rewarded with a bill for Eur 70.
Fit a new cluster
You should be able to get a used cluster without the bug from a breaker for about 100 EUR, then you can have it reprogramed to 300000 for about Eur 45. And again see to it that it comes from the same type of car.
Build your own codeplug !
I've found some very interesting information about the codeplug from a russian site called "Diakom" (via a fench site from J. Weiss). Ofcourse I found this just after I droped my original plug off to be reset. The document can be viewed here
Check out section 4:"The most mysterious shitok with the chip in a socket by name HML 075 F" of the document. It explaines how the milages is stored in the original chip using the dump from a codeplug. It also has assmebler code and instructions on how to replace the original codeplug with an Atmel 90S2313 microcontroller. This emulator will allow your cluster to run beyond 300 000.
One thing that was unclear to me while soldering the plug is how they could talk of pin 20+ on the codeplug while it only has 18 pins. After investigating the PCB of the codeplug it revealed that the lower row has pins 4 to 12 and the upper row has pins 16-24 of the HML chip.
I've been incontact with a member of the "7er forum" called Fred. He has also build a plug with an Atmel chip. And has provided me with some fixes on the original design. He also rebuild some old computer to read from the original chip.
Fixes over the original diakom design:
Leave out the R102 resistor
With this resistor in place the plug won't work.
Change pin 7 and 9 (PD3/INT1 and PD5/T1) on the Atmel.
This will stop the "Kuhlwasser temp" checkcontrol errors from apearing.
It will also prevent the SI from resetting itself.
Interesting links:
Threads about the problem from the 7er.com forum in German:
Thread 1 about the 299960 problem
Thread 2 about the 299960 problem
The french site where I found the pages translated from russian:
Combiné d'instruments BMW E32/E34
Story by Johan