How to flash a new Toyota ECU?

[Fru-Gal]

I am trying to replace my engine control unit on my new/old 2003 Toyota Rav4, 100k miles, due to rough shifting, incorrect shifting (starting in 2nd/3rd gear instead of 1st), shuddering — signs of imminent transmission failure. According to Rav4 forums, this is often due to the ECU which was recalled possibly due to bad solder.

It may be my transmission, of course, which turns out to be a replacement as well (dealer lied) but that’s more expensive and the shift solenoid failure codes that I’m getting are also often thrown by the ECU going bad. I also had the transmission fluid flushed not long ago and while my mechanic says it’s the transmission, not the computer, he also says it doesn’t smell like it’s the transmission (weird burnt toast smell). I notice he often will make snap judgments (he did this after driving it and smelling transmission fluid, no other tests), though he has done good work for me so far, so I did more research.

I pulled out the ECU and discovered it is a replacement or repair from EBay (it’s labeled as such with paint marker, as is the transmission).

My options are to buy a replacement (salvage, tested) one that will not be flashed for my vehicle or have the one that I took out tested and repaired. I have ascertained that it is the correct ECU part number for my car. A new OEM one is quite expensive.

My question is, how do you flash a new one for your car? It is not clear to me if when you install it correctly and then turn the key and wait 30 seconds if the car itself will flash it for the correct VIN number? Or does it need to be done with some kind of diagnostic computer (via OBD port)? Or could O’Reilly do it for me (they read engine codes for free)?

[Paper Chaser]

A salvage ECU from the exact same vehicle/engine/transmission combination would probably not need to be flashed for a vehicle from 2003.
If the ECU is brand new, never installed in a vehicle, then it will probably need to be flashed. That needs to happen at a dealer.

[Fru-Gal]

Thanks for the reply. Yeah my mechanic said this year was plug and play so you may be right.

We have come up with a plan… mechanic is going to get a different ECU from a local supplier he knows where he can return it if he doesn’t want it. We will install that one and see if the transmission improves. (Apparently it’s only a matter of a short amount of driving for the ECU to learn to work with the transmission.) I will pay him for his time. If it works, I buy the replacement ECU as well.

If not, it’s on to replacing the transmission. He pointed out that we don’t know how many miles are on the replaced transmission, nor can you easily get a used transmission of this vintage with low mileage. So he still thinks that’s the failure, not the ECU.

Note that the CarFax on this car was very clean and showed only two owners (local to me), with very low driving mileage for its vintage. My theory is that it was owned by an elderly person or someone who died and it sat for a long while, which is almost as bad for a car as being driven too much.