I'm thinking about buying a spare ECU to have that one flashed and stock one left alone. Just wondering if I can use a 04 WRX ECU in a 05 WRX car? Both will be manual transmission. Thanks.

There were some problems when Cobb used an 05 image for 04 cars, so I don't know if 04 ECUs will work in 05's well. That being said, if you are going to use an Accessport, I think it can write 04 firmware onto an 05 ECU and vice versa. I think the same goes for EcuTek. I would check with your tuner first. That is probably the safest thing to do.

Mike

it should work,esp if you get like an ECUtek... it wouldn't work on an STi but WRX should e fine, 02-03 will work too

i'm pretty sure you can use an 04 on an 05, but NOT an 05 on an 04.

05 WRX's are drive by wire, 04 WRX's are drive by cable. The 04 ECU does not have any drive by wire crap so I don't know if that will have any effect. I would say it will either work OK or it won't work at all. Do some research to see how the drive by wire works (i.e. does it use the ECU in the process or not) to see if the 04 is a viable option.

05 WRXs don't have drive by wire. It didn't get implemented until 06 with the 2.5L engine.

OK, I suck. In that case it should work just fine.

There are some threads somewhere around here about that very thing .... not sure where or what worked with what, a search may be in order ;)

bump...

what was the outcome here?

Are 2004 <--> 2005 ECUs interchangeable?

02 and 03 ECU are interchangeable right?

02 and 03 ECU are interchangeable right?
Old ECU into newer car. and 02 can go in anything up to 04. I have seen an 02 in an 04 car and it ran better than stock. It should work in an 05, but I have not seen it. But every years they add new sensors, so newer ECUs will not work in older cars without CELs from the missing sensors.

Back to the original poster, how about backing up the actual stock ECU image with the software from www.openecu.org and the tactrix cable? Cheaper than a spare ECU...