Ways to reset the ECU

[YKhan]

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

 

[Carl 1 Lucky Texan]

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

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

 

[MD]

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.

 

[AS]

Can the racing up be caused by a vacuum leak? Accelarator sticking?
Throttle body leak?

 

[YKhan]

Can the racing up be caused by a vacuum leak? Accelarator sticking?
Throttle body leak?

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

 

[YKhan]

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.

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

 

[YKhan]

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.

Ah yes, okay, that makes sense. Thanks.

Yousuf Khan

 

[Yousuf Khan]

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

 

[Carl 1 Lucky Texan]

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

Wow! Good news on the radio - interesting.

thanx for giving the results.

Carl

 

[Yousuf Khan]

Wow! Good news on the radio - interesting.

thanx for giving the results.

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