Hi all

For the past year I've had an annoying intermittent problem with my Mk4/v31 system.

On longer directed journeys (over an hour or so) the active guidance will crash without error leaving the right-hand side of the nav screen blank. The maps continue to be correctly displayed, along with the original white line, as does the name of the current town and the current time. The ETA starts to advance from the point of failure rather than counting down to zero. VR requests to repeat "instruction" are ignored and voice guidance stops. The screen does not go blank and no obvious errors are seen. Dynamic rooting stops and only a 10 minute ignition off / restart will clear the error.

The strange thing is that this only happens on longer directed journeys and seems to be worse if TMC messages are received or diversions are taken. Local journeys of 20 miles or so with frequent route changes are fine - we always get the "you have arrived" message.

At first I thought my customised v31 was causing this problem due to over large images (splash) but this error happens with reduced image sizes and standard v31.

I am currently using a backup 2009-01 dual layer DVD but backup 2008-02 (single layer) also led to same intermittent problem. The MK4 is about 4 years old. Disks often eject with a fair amount of dust due to low humidity from A/C.

After a crash the GPS signals and wheel / direction info is all ok.

I suspect a faulty memory chip or a bad / dirty laser but I never had any problems with v29 or eariler versions - coincidence?

I wonder if the dual layer mod in v30 has made the nav system more sensitive to the quality of the DVD or the cleanliness of the laser.

Is there any diagnostic test that can be performed on a Mk4 to check all memory addresses are ok?

Appreciate your thoughts

Thanks
David