99 Nissan ECU Pathfinder/ Infiniti QX4 MECM W435 Up for sale is a Working, in excellent condition Nissan Pathfinder ECU. Should fit many 1999 Pathfinder / QX4 models, perhaps others as well. See part numbers at the top of the listing and compare this to your original. - . This unit offers a 30 day functionality warranty. INFINITI QX4 99 Elec Cont Unit (ECU); (behind ctr dash), Fed, from 12/98PATHFINDER 99 Elec Cont Unit (ECU); (behind ctr dash), from 12/98, AT, Fed, 4x4As always with this type of component your best bet is to match the part number to the one on your original ECU. 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. These units now have to be special ordered from most dealers new for big $$ (often times over $1000!), and you can never find one when you need one. Even now finding a good one second hand is getting to be quite difficult as these cars get older.