My coolant warning light has suddenly illuminated, telling me to "STOP" and "consult service manual". I have checked the coolant level and it appears to be OK. I recently had the car serviced (long-life 40K miles) at a "German Car specialist" but probably not a VW approved garage. They were unable to access or to change the service mileage indicator - is that relevant? Is there any obvious reason I am missing, like, for example, can the computer detect if the coolant antifreeze concentration is wrong? I'd appreciate some knowledgeable help. Thanks, John