Author Topic: How to - Golf Mk3 Instrument Cluster Odometer Mileage Adjustment  (Read 798 times)

Offline mcrispVR6

  • Just got here
  • *
  • Posts: 5
This is useful for anyone replacing broken cluster, or installing mk3 cluster to mk2 VR6 which is what I needed to do.

Mods and admins please forgive any rules I have broken and let me know what needs changing.  I figure with MOT checking mileage now there's not a great deal to be gained in altering clocks that can't be achieved by swapping or disconnecting clusters anyway.  Most people working with equipment this old are more likely to have an interest in maintaining genuine mileage records than the opposite. 

Thanks to RubJonny and Steven Harper who have both helped with info.  Thanks to RubJonny for helping solve a million of my electrical problems in the last 10 years without even knowing it.

I have searched extensively and couldn't find a full written how-to anywhere.  Steven has already posted a good Youtube video here but there's a few tricky bits that I'll try and explain here.   There was another similar video on youtube where someone used a serial-parallel converter that I saw once and alas could never find again - anyone know where?

I have a motometer cluster so used the mm.exe programme.  There is a vdo.exe programme for VDO clusters which works more or less the same but I didn't try so can't really comment.  See google share folder here for the programmes and the instructions (in german...)

You will need an old PC, something running about 90 or 133MHz processor at most (nothing any faster will work), with Windows 95 or 98 and a 25 pin parallel port (old style printer port).  If it hasn't got a USB port then look for one with at least a CD drive as that's the only way you're going to get files onto the computer - forget trying to get the internet working on a machine that age.  I got hold of an old 90MHz Toshiba Satellite Pro 410CDT laptop with windows 95 which did the trick.  There's plenty of these 'vintage' laptops around on ebay and a good market for them, if you have to buy one you will be able to sell again no problem.  Or you could put VAG-COM on it with a serial lead interface and have it as a trendy 'vintage' accessory in the glovebox of your classic VW...

In summary it appears that some clever German dude, long long ago, has written a C++ DOS programme that flashes (programmes) the EEPROM memory chip on the instrument cluster via the parallel port on a computer and the programming port on the cluster, without the need for removal of the EEPROM.  (Remember computing lessons at school in the late 80's where we made BASIC programmes that would make LEDs flash on and off with the parallel port?  No?  Well you should have been there, it was cool.)  The port on the instrument cluster was apparently for initial programming and reprogramming by the dealer which apparently VW had limited ability to do if necessary to reset delivery mileage or replacing faulty clusters.

Parallel ports have 25 pins, you can read the pin numbers here:

The Mk3 cluster (and the Corrado cluster, and actually also some Mk2 clusters I've noticed) have an access port on the back of the cluster to 4 connection points on the circuit board.  You need to open up the cluster casing and solder wires on to each of those connection points.  Be very careful not to damage the circuit board - use small wires and small soldering iron...  The access port has a little slot at one end.  We shall number the connections as 1 at the end with the little slot, through to 4 at the opposite end.  The other ends of the wires you can just remove insulation and make them the right thickness to push into the computer parallel port pin sockets.

Wiring connections parallel port to cluster (see guide in share folder above but watch out they drew the parallel port the wrong way round which is a bit misleading):   
  • Parallel port pin 25 and 24 to instrument cluster point 1 (connecting to both 25 and 24 just makes sure you've definitely got a good connection to the parallel earth)
  • Parallel port pin 2 to instrument cluster point 2
  • Parallel port pin 3 to instrument cluster point 4
  • Instrument cluster point 3 - no connection needed
Programming process:
  • Make the wiring connections with the laptop and cluster switched off
  • Plug the instrument cluster into the car wiring loom or put 12 v positive and earth to the relevant pins - safer and easier to just plug it into the car I think. for the instrument cluster pin identification if you need them to connect constant live, ignition live and earth to the right pins.  Power off for now.
  • Start up the computer and go to BIOS menu - hit the F2 or F8 key (or other - google your laptop model to find how to get to BIOS menu) as the computer starts up.
  • Set the parallel port to standard bi-directional protocol.  Depending on some PC models, parallel ports may have newer EPP or ECP or other protocols which didn't seem to work for me.
  • Save BIOS changes and let the computer boot up in windows.
  • In control panel/system/device manager find the LPT port.  Check the IO address is correct - LPT1 needs to be set to 0378H which it will usually be - read wikipedia article on parallel ports and this article for a mind blowing level of detail
  • Save the mm.exe programme directly on the windows desktop for easy access - use USB port, CD drive or floppy(!!!) drive to get the files onto the machine.
  • Go to shutdown and choose 'restart in MD-DOS mode'
  • Type "cd desktop" and enter at the MS-DOS command prompt
  • Type "mm" and enter to run the programme
  • Programme will ask you 'km-stand eingeben' which means enter km you want the cluster to change to (you can type miles for a cluster that runs miles not km, it will work).  Enter a number and press enter
  • Programme will ask you 'Bitte zundung blah blah' which means turn on the ignition power to cluster. Once you've done this, you should see the cluster display will switch to say --P-- which means it's gone into programme mode - this means your computer has initiated communication with it, thats good. Press enter.
  • What should happen is that your computer will hesitate and show a few dashes on the command line as it sends the info.  Then, the display will change to show the new mileage. 
  • See Stevens video, try sending 80085 for fun and giggle when it says BOOBS on the display...
What I found is that occasionally at the last step the computer can hang or crash and the cluster display continues to show --P--.  In which case turn off the computer manually by press and holding the power button, and turn off the power to the cluster, and you should find the correct mileage comes up on the cluster and it has actually worked. If not, try the whole process again - it took me a few attempts, I'm not sure why.  Maybe I shouldn't have the cluster plugged into the car with power running through the various sender circuits, not sure.

Be careful to keep everything still and not disconnect wires or turn anything on and off while the programme is running - you run the risk of scrambling not just the mileage but other info stored on the cluster eeprom (memory).  Same applies for parallel port - if you short anything or mis-connect, you could fry your parallel port card on the computer, although they should have protection against faults.

Now it has occurred to me, that you might just be able to do something similar with a MK2 cluster that tells the eeprom memory chip its working with 6 cylinders rather than 4, which would be a lovely little solution to the usual problem with the mk 2 cluster rev counter on mk2 VR6 conversion and doesn't involve diodes and wires from the coil to the cluster (which I tried and fried my mk2 cluster with and hence why I've gone down the Mk3 cluster route instead).  There is lots of info out there about the hex data for cluster eeproms, any info on this theory would be greatly appreciated.  The cylinder number in the eeprom might not have anything to do with the way the cluster calculates the tachometer indication from the rev pulse signal but who knows.
« Last Edit: 01 November 2020, 09:32 by mcrispVR6 »

Offline itavaltalainen

  • I live here
  • *****
  • Posts: 2,674
  • VCDS and VCP - fault codes, coding, VIM activation
I've changed mileage and k-value on a few clusters e.g. when upgrading from non rev meter clocks to ones with or swapping for an MFD cluster.
I'd only ever do it by reading the EEPROM directly and writing the modified file back. No issues with the PC or PP being an issue and you can use a modern OS ;)
2019 Seat Leon ST FR DSG 135kW - eclipse orange - 23k miles

Offline beukie

  • Just got here
  • *
  • Posts: 1
Hello, i want to change te km in my cluster with a eeprom reader but how can i get it working?
I try to read the 93s56 eeprom but with no succes, do i Need to solder the eeprom of the bord or can i use the clamp? Can some one help me with this?
Btw i want more km on the cluster