1. Home
  2. Subaru Cars Forum
  3. Ways to reset the ECU

Ways to reset the ECU

Reading through past postings on the subject a lot of problems seem to be fixed by resetting ECU. I think I'm experiencing one of those problems with my racing-up idle engine speeds. There are two major suggestions for resetting this thing:

(1) unplug the battery from the negative terminal for X minutes.

(2) unplug the ECU's fuse from the fuse box.

For #1, the suggestion range from unplugging the battery for anywhere from 15 minutes to 30 minutes to 1 hour. Why not only 5 minutes, let's say? Also why the negative and not the positive terminal, what's the difference, electricity stops flowing regardless.

Also some of you suggest that I press the pedal down after unplugging the battery. Which peddle, accelerator, brake, or clutch? And Why? What difference is depressing one of the peddles going to make when the battery is unplugged? There's no electricity flowing through the system anyways.

For #2, just pulling the fuse seems the most convenient. That way I don't have to reset the clock or the radio or stuff. However, looking through the owner's manual, I don't see any fuse labeled "ECU fuse". I do see a dual-use fuse labeled, "Engine Ignition System/SRS airbag". Would this be it? My car is a 2000 OBW, was a specific ECU fuse a part of an earlier generation of Subarus but not mine?

Yousuf Khan

Reply to
YKhan
Loading thread data ...

Well, without doing the experiment my self, I don't really know what the minimum amount of time would be. Are you in a hurry? Some folks disconnect overnight. The brake pedal being depressed might drain any charge in a capacitor on the input of the radio or elsewhere (???) The negative side of the battery is always suggested, even for other purposes as in replacement, because you are not able to create a short with the wrench from the pos. side to the chassis if the neg. side is disconnected.

A third way to reset the ECU is with with most medium priced OBD II scanners.

Carl

Reply to
Carl 1 Lucky Texan

I just pull the fuse. I have a Legacy and it is in the engine compartment fuse box, under the hood. There should be a map on the lid of the box telling you which fuse is for the ECU.

Reply to
MD

I don't know, usually in the past it's been something stupid like a throttle position sensor or O2 sensor or something like that. This time the dealer could find nothing wrong with them, and there were no codes in the computer. So they just told me to not worry about it, it'll go away on its own. That was was 3 months ago, and for the most part it did go away on its own, but now it's back again, yet still no check engine light showing up. I'm just going to reboot my computer to see if that helps.

Yousuf Khan

Reply to
YKhan

The map doesn't show anything labeled ECU fuse, not under the cover of the fuse box, and not in the owner's manual. There is an automatic transmission memory fuse (fuse #26 under the hood). Since I don't have an automatic transmission, I don't see why my unit would still have a fuse for it.

Yousuf Khan

Reply to
YKhan

Ah yes, okay, that makes sense. Thanks.

Yousuf Khan

Reply to
YKhan

Hey, so here's an update. I did reset the ECU through the battery disconnect method. I could not find any fuse either in the engine fuse box, or in the cabin fuse box that could've been for the ECU, though a couple sounded very close. Also I didn't need to hold down any pedals after disconnecting the battery. I just left it unplugged for a little over 15 minutes.

The result after resetting the ECU? My car is now completely fixed, running normally again. The idle speed problem is now completely gone (albeit it's only been half a day so far). I ran around a few blocks near my place to test it out. Plenty of stop'n'go driving to test multiple speed ranges, the idle never raced up during that time.

In a way I'm glad I went with the full battery disconnect method rather than the fuse pull. That's because it also fixed a niggling problem I've been having with my car MP3/CD-player stereo. It's display had stopped displaying the song names properly. The power outage fixed that right up quickly. I had previously thought that the stereo had been permanently damaged, but it looks like it just needed a reboot too.

Yousuf Khan

Reply to
Yousuf Khan

Wow! Good news on the radio - interesting.

thanx for giving the results.

Carl

Reply to
Carl 1 Lucky Texan

This MP3 CD player has been quite problematic for me ever since I got it, and it's all related to Canadian weather. When it gets too cold outside, the electronics inside it go haywire. That's why I try to get an indoor heated garage wherever I live. Even then, I still sometimes see problems crop up. I had never dreamed that it could be fixed by simply cutting the power off to it.

Yousuf Khan

Reply to
Yousuf Khan

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.