ECU Reset (Without Disconnecting Battery)
 

Here is how to reset your ECU without disconnecting your battery. This is a solution for those who install new parts and do not want to risk losing their trip meter mileages, radio presents, and so on.

1. Make sure the car is off and that the key is not in the ignition.
2. Open the hood and locate the "Engine Room Relay Box." This is the fuse/relay box in the engine bay. On the xA/xB, it is the black top box to the right of the engine bay.
3. Take the black cover off and flip it over to read the embossed diagram. You want to look for the EFI fuse (not RELAY). On the xA/xB, the EFI fuse is 15 Amps. On the tC, the EFI fuse is 20 Amps.
   On the xA, the EFI fuse is #4:
   https://www.scionlife.com/tech/image...set/efi-xa.gif
   
   On the xB, the EFI fuse is #12:
   https://www.scionlife.com/tech/image...set/efi-xb.gif
4. Using the fuse-puller (white piece of plastic in the box), pull the EFI fuse out and let it sit for 10-30 seconds.
5. Pop the fuse back in the EFI fuse socket. Make sure it is properly seated and is uniform with the other fuses.
6. Put the black cover back on.
7. Cross your fingers, start up the car, and hope you don't pull another CEL (Check Engine Light).
8. If you are successful in not pulling a CEL, I recommend you let the car for 5-10 minutes for good measure.

Some people have told me this does not work on the tC. Whether or not they did it right is beyond me. This has worked with other cars... If someone can get back to me on this, that would be very helpful.
Update:

wouldn't it be faster and easier to disconnect the battery since you're under the hood anyways?

thanks for the info mikochu ...... :D

oh tyte. i've been wondering which fuse it is to reset. thanks!

i like the fuse method better than the battery-disconnect method; pulling out a fuse can be done without busting out my toolbox.

Ummmmm here is the reason why some don't disconnect the battery.

nice idea
i understood everything and i am fine
but, what you meant by "those who install new parts"?
what parts? like what??

i did it that way when i installed did the poor mans intake mod, i unplugged the maf and then did the fuse thing and it felt as if i lost power ...so i redid it but just unplugged the maf without doing the fuse thing and it pulls much better..... i thought it might have been that i didn't wait enough so i did it a few times and it was that. strange but i am against pulling out your efi fuse from experience!

I read on Consumer Reports:

Obtain a fresh unused 9V battery (those rectangular shape battery). Obtain a 9-Volt Vehicle DC-to-DC Adapter (one end plugs in your cig. lighter; the other end has connection for a 9V battery. Plug the 9V to the adapter> Plug the adapter to the cig lighter. It should work, according to CR.

so if i isntaled an cold air intake and a new exhuast system..then i need to do this right?
i feel that my rpms and motor is running funny.

Definitely after a CAI install...

ok i just gave it a try... CEL has not come on yet.. going to let it run for a the time you say to.

hmm seemed to clear up a few problems if it is the same in the morning il have to make the sure the CAL is set right and screws are tight and no air leaks.

mikochu thank you for this info.

If you dont do it after CAI install what will happen?

umm...this came in handy yesterday unforunately i read it today..

after any install of aftermarket parts all the parts need to be recalibrated in order for your or any computer ran car to run its most efficient. things such as fuel maps air for sensors and such need to be recalibrated and the only way to do so properly is to reset you ECU after a install or mod and drive the car normally until the car has gotten a chance to set all the settings to correspond with the new modificatons or installation.

^^^ does that include things like carbon fiber door sill plates? :P I

Mikochu, in the unlikely event that you are still monitoring this post, this fix 100% works for the tc. I used it this weekend when installing a SRI. Thanks!

Is there anyway to be sure the ECU reset after doing this?

Well, I can 100% vouch for this working on the TC. I had a CEL on mine before I did this , and rather than disconnecting the battery, I decided I'd see if this method worked. Pulling that fuse removed the CEL, so yeah, it works :)

Oh, thanks! Although, I was actually looking for some kind of "landmark" that I could look for after reseting it to assure me that I did it right. I'm installing a CAI so I'm guessing a power gain would be something to lookout for. I'm guessing that If the engine doesn't run well anymore or my gas mileage dramatically drops...I can tell the ecu didn't reset....???

There really isn't any kind of landmark or anything. But trust me, if you pull that fuse at the beginning, and leave it out until you are done, the ECU will be reset.

Just remember to let the car idle for 5-10 minutes before you drive it. Regarding Gas mileage....most likely your first two tanks are gonna be significantly lower...I say that because when you hear how aggressive the new intake is, you're gonna jamming the gas all the time, and winding it up. I typically averaged about 23-24 or so in town, prior to the intake. MY first two tanks after wards were 20.x But that's because I was shifting at 4-5000 rpm's, not 2800. Once I got over the noise/aggressiveness, the gas mileage went back up to 23 ish.