I own a 2003 Mazda 6 with 160,000 miles. I have been battling with various engine diagnostic codes for a couple of years. The local dealership has been unable to correct the problem. Recently I took the car to a local private garage that does engine diagnostics. After 4 hours of diagnosis, they have determined that my ECM is shot. They referred me to the dealer for replacement. I have little confidence in the local dealers. Does the dealer have to replace the ECM, or can I do it myself?

 

They may have to re-program your keys with new ECU.
JUST FOUND it: https://www.mazdaforum.com/forum/maz...pcm-ecu-24689/ Read it!

 

W/O reading Noggin's link I can tell you that a new ECU/PCM would need to have the information contained in the old unit downloaded to the new, such as the VIN, transmission type and mileage information, options controlled by the ECU, etc.
When they did my wife's Vibe under warranty, it took <5 mins to physically replace the unit and another 45 mins to program it for her car.