Audi ECU Up for sale is a Working, in excellent condition Hitachi Control Module for Audi 90 20 valve 5 cyl engine ECU. Audi part number 893 906 266B / 893 906 266 B / MMS04B / MMS-04B ENGINE CONTROL your best bet is to match the part numbers with the original unit in your car. This unit also comes with a 30 day functionality guarantee! This is located on the passenger side behind the glove box. This was removed from a recent crash damaged 1990 Audi 90 20 valve quattro. (build date was in 1989) - I have this exact car I daily drive and it's a great car, but as with any Hitachi ECU controled car, always carry a spare with you!This unit from the ePartsland "rare as hens teeth collection!"***!!!RARE ECU ALERT!!!***A faulty ECU is one of the most common no start or random stalling problems with these cars. These can also cause issues with erroneous check engine lights, idle control problems as well as emission control & cold or hot start problems. I have also seen fuel pump relay turn on faults (ECU won't turn on the fuel pump), as well as an condition where the high speed injector driver has failed. This causes the car to sit and idle fine, but it won't accelerate.If your car does not have these issues but you intend to keep it a while, I recommend our customers keep an extra ECU in the trunk. If you need to buy a NEW unit, these typically have to be special ordered from most dealers which may take over a week, and topical cost is over $2000. I'd recommend you Keep a spare, right next to your spare tire considering this fact. If you need one of these units now, you probably won't beat this price for a good used unit with a 30 day functionality warranty!