Welcome to the North American Subaru Impreza Owners Club Wednesday September 17, 2014
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
Go Back   NASIOC > NASIOC General > Newbies & FAQs

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads.
Reply
 
Thread Tools Display Modes
Old 08-19-2011, 12:44 PM   #1
the suicidal eggroll
Scooby Guru
 
Member#: 51961
Join Date: Jan 2004
Chapter/Region: RMIC
Location: Broomfield, CO
Vehicle:
2005 STi
2012 WRX

Default PSA: Stop resetting your ECU

This is a public service announcement for all of you out there who think that resetting the ECU is a logical debugging step when you encounter a problem with your car.

It's Not

Resetting the ECU is NEVER a valid response to a problem. It will never fix the problem, it will never give you insight into the problem, it will do NOTHING but hide the problem for a few miles before it comes right back, or it could even make the problem much worse than it was before.

There are VERY FEW situations in which resetting the ECU could be considered a logical move. These include:
1) AFTER tracking down, and FIXING a problem with your car (IE: bad O2 sensor, vacuum leak, etc), it's a good idea to reset the ECU to clear all of the learned parameters (which it learned while there was a problem) so that it can start from scratch.
2) After changing the octane of the fuel your car is running, either higher or lower. If you're raising the octane, resetting the ECU will clear out the timing changes the ECU had to make to compensate for the low octane, and allow you to take advantage of the higher octane sooner. If you're lowering the octane, resetting the ECU will put it into an active knock learning mode, which will let it adjust for knock quicker than if you just left the ECU alone. Note that if you're lowering the octane, do NOT, under ANY circumstances, perform the "vishnu" trick after resetting the ECU.
3) After making a major part change on your car and flashing a new tune to suit. Now most tuning methods will reset all of the learned parameters when you flash the new map on the ECU anyway, so in this case, the reset is already taken care of for you.

There might be a couple others, but not many.

Here are a few situations in which you should NOT reset the ECU:
1) Your gas mileage has dropped and the car is not running as well as before - resetting the ECU will do absolutely nothing but erase all evidence of what could have been causing the problem, and the problem WILL come back
2) The ECU has thrown a check engine light - If it's an important CEL it WILL come back, and if it's not an important CEL it will disappear ON ITS OWN after just a few key cycles.
3) The engine is running rough and/or misfiring - Like #1, resetting the ECU will do nothing but erase all evidence of what was causing the problem, and the problem WILL come back
4) The car is stalling - See #1 and #3 above
5) The boost is not hitting target (either high or low) - There are no learned boost control values like there are for fueling and timing that could be zero'd out with an ECU reset. There is only the on/off switch from DAM/IAM. If your ECU has completely disabled boost control due to excessive knock, resetting the ECU will set the DAM/IAM back to its default value, which will temporarily restore boost control. This is a BAD thing though, because there's a reason the ECU deemed it necessary to cut off boost...it detected excessive knock and determined that the engine was in danger. You don't want to bypass this safety feature, you need to find and fix whatever is causing the excessive knock.

And many, many others.

The basic rule of thumb is that unless you've recently made a major change to your car that will affect its operating conditions (either fueling or knock-related), AND it's your intention to clear out the old learned parameters to give the ECU a "fresh slate" so-to-speak, you should never reset the ECU.


Sorry about the rant, I've just seen way too many threads recently where the owner encountered a problem with their car, and their first reaction was to reset the ECU. This will ALWAYS either make the problem worse, or do nothing at all. It will NEVER fix the problem, and it will erase all evidence of what was causing the problem, making troubleshooting next to impossible.
* Registered users of the site do not see these ads.

Last edited by the suicidal eggroll; 10-25-2013 at 06:09 PM.
the suicidal eggroll is offline   Reply With Quote
Old 08-19-2011, 12:46 PM   #2
kpluiten
Scooby Guru
 
Member#: 120273
Join Date: Jul 2006
Chapter/Region: SWIC
Location: AZ
Vehicle:
06 WRBWRXWGN
Now with 100% more Spec-C

Default

Thank you for this. I wish more people would understand this. Simply turning of the CEL does not fix the problem!
kpluiten is online now   Reply With Quote
Old 08-19-2011, 12:54 PM   #3
taosracer
Scooby Newbie
 
Member#: 131108
Join Date: Nov 2006
Chapter/Region: NESIC
Location: the DRS zone
Vehicle:
2002 TS/WRX wagon
Blue ridge pearl

Default

Good advice. Nothing more irritating than trying to fix a car and having to put many drive cycles on it to get it to throw the DTC again !

Having just moved from Colorado to New England, and seeing how that has affected my car's boost levels and performance, I think that making a major altitude change would also be a valid reason to do a reset.

Thanks
taosracer is offline   Reply With Quote
Old 08-19-2011, 01:35 PM   #4
Meiki
Scooby Newbie
 
Member#: 289311
Join Date: Jul 2011
Location: Houston
Vehicle:
2011 Subaru WRX STi
White

Default

How do you even reset ECU? Sorry for stupid question.
Meiki is offline   Reply With Quote
Old 08-19-2011, 01:40 PM   #5
teesutt
Scooby Specialist
 
Member#: 127940
Join Date: Oct 2006
Chapter/Region: MWSOC
Location: One Big Ass Mistake America
Vehicle:
*
Evil shenanigans

Default

Quote:
Originally Posted by Meiki View Post
How do you even reset ECU? Sorry for stupid question.
pull negative battery terminal, press brake pedal, reconnect neg terminal, start car. Or a reflash.
teesutt is offline   Reply With Quote
Old 08-19-2011, 01:42 PM   #6
dpbacon
Scooby Newbie
 
Member#: 241511
Join Date: Mar 2010
Chapter/Region: RMIC
Location: Denver, CO
Vehicle:
2010 WRX Premium
Dark Grey

Default

Quote:
Originally Posted by Meiki View Post
How do you even reset ECU? Sorry for stupid question.
Remove the battery terminal and press the brake peddle a few times to bleed the system of any remaining electrical charge.
dpbacon is offline   Reply With Quote
Old 08-19-2011, 01:42 PM   #7
the suicidal eggroll
Scooby Guru
 
Member#: 51961
Join Date: Jan 2004
Chapter/Region: RMIC
Location: Broomfield, CO
Vehicle:
2005 STi
2012 WRX

Default

Quote:
Originally Posted by taosracer View Post
Having just moved from Colorado to New England, and seeing how that has affected my car's boost levels and performance, I think that making a major altitude change would also be a valid reason to do a reset.
An altitude change shouldn't have an effect on anything that would be changed with an ECU reset. There are no learned boost parameters, so resetting the ECU will not affect boost, and any knock or fueling corrections that were learned at altitude should still be valid at sea level, so a reset shouldn't be necessary.

Quote:
Originally Posted by Meiki View Post
How do you even reset ECU? Sorry for stupid question.
Disconnect the battery for a few minutes, or you can use a tactrix cable or an accessport to reset it through software.
edit: hah, little late to the party on that one
the suicidal eggroll is offline   Reply With Quote
Old 08-19-2011, 02:07 PM   #8
JarHarms
Scooby Specialist
 
Member#: 138994
Join Date: Jan 2007
Chapter/Region: MWSOC
Location: DeKalb-ish, IL
Vehicle:
06 WRX Ltd SGM 6MT
02 Forester S

Default

Curious, does an ECM reset also dump the OBD monitor ratios back to zero? I guess it might be similar to performing a clear CEL message.

Quote:
Originally Posted by the suicidal eggroll View Post
It resets everything. All learned parameters, including fueling adjustments, timing adjustments (knock correction), idle throttle plate position, as well as CELs/DTCs are cleared. It will reset the IAM back to 0.5, cutting your timing advance in half and robbing the car of 10+ whp, and it will also throw the ECU into a "not ready" state, which means you can't pass emissions until you drive for ~100 miles. Is this what you're asking?
Yes, thanks that is what I was looking for. I was sure on the other items you listed. But I have never compared the monitor ratios or as you called them the ECM's "not ready" state. I just did not want to assume anything.

Last edited by JarHarms; 08-19-2011 at 04:05 PM.
JarHarms is offline   Reply With Quote
Old 08-19-2011, 02:21 PM   #9
the suicidal eggroll
Scooby Guru
 
Member#: 51961
Join Date: Jan 2004
Chapter/Region: RMIC
Location: Broomfield, CO
Vehicle:
2005 STi
2012 WRX

Default

It resets everything. All learned parameters, including fueling adjustments, timing adjustments (knock correction), idle throttle plate position, as well as CELs/DTCs are cleared. It will reset the IAM back to 0.5, cutting your timing advance in half and robbing the car of 10+ whp, and it will also throw the ECU into a "not ready" state, which means you can't pass emissions until you drive for ~100 miles. Is this what you're asking?
the suicidal eggroll is offline   Reply With Quote
Old 08-19-2011, 02:38 PM   #10
Raptor89
Scooby Newbie
 
Member#: 285405
Join Date: Jun 2011
Chapter/Region: MAIC
Location: Pittsburgh, PA
Vehicle:
2013 WRX Hatch
WRB

Default

What about a reset after having to unplug the MAF to change the passenger blinker bulb, which causes the CEL and TCS lights to illuminate, and the Cruise Control to blink and not work? Obviously there's nothing wrong (other than the common faulty blinker bulb), as the car had less than 3,000 miles on it. Is a reset in that situation okay?
Raptor89 is offline   Reply With Quote
Old 08-19-2011, 03:28 PM   #11
drewvdw
Scooby Guru
 
Member#: 255776
Join Date: Aug 2010
Chapter/Region: MWSOC
Location: Laramie, WY
Vehicle:
2010 LR WRX
MPS powered.

Default

Ecu reset is never a bad thing when you mod your car, ie finish installing a turbo inlet and resetting ecu as unabomber mentions in all his faq's. Not only a major part change.
drewvdw is offline   Reply With Quote
Old 08-19-2011, 04:18 PM   #12
the suicidal eggroll
Scooby Guru
 
Member#: 51961
Join Date: Jan 2004
Chapter/Region: RMIC
Location: Broomfield, CO
Vehicle:
2005 STi
2012 WRX

Default

Quote:
Originally Posted by Raptor89 View Post
What about a reset after having to unplug the MAF to change the passenger blinker bulb, which causes the CEL and TCS lights to illuminate, and the Cruise Control to blink and not work? Obviously there's nothing wrong (other than the common faulty blinker bulb), as the car had less than 3,000 miles on it. Is a reset in that situation okay?
I've unplugged my MAF many times for one reason or another, and it's never set off a CEL (it will if the engine is running at the time, but it shouldn't make any difference if the key is off). Is this a quirk in the newer ECUs?

Quote:
Originally Posted by drewvdw View Post
Ecu reset is never a bad thing when you mod your car, ie finish installing a turbo inlet and resetting ecu as unabomber mentions in all his faq's. Not only a major part change.
Completely unnecessary to reset the ECU after a turbo inlet install, you won't gain a single thing by it. If you really want to, knock yourself out. This post is more about people resetting the ECU to fix a problem they're having.
the suicidal eggroll is offline   Reply With Quote
Old 08-19-2011, 04:36 PM   #13
XanRules
NASIOC Supporter
 
Member#: 157348
Join Date: Aug 2007
Chapter/Region: NWIC
Location: Benghazi
Vehicle:
1996 JNCO Jorts
Stonewashed Denim

Default

Thank
XanRules is offline   Reply With Quote
Old 08-19-2011, 04:59 PM   #14
fredtga
Scooby Specialist
 
Member#: 156274
Join Date: Aug 2007
Chapter/Region: SCIC
Location: Los Angeles
Vehicle:
2002 WRX Wagon
WRB

Default

so, let's say i have a subaru that i'm using only for about 2-3 times a month... track day, rally event you name it, but it is not daily driver...

is it bad to disconnect the battery every time i have it parked ? the battery is a small one and if i leave it connected on the car for about a week, it would barely rotate the engine for start...
fredtga is offline   Reply With Quote
Old 08-19-2011, 05:11 PM   #15
drewvdw
Scooby Guru
 
Member#: 255776
Join Date: Aug 2010
Chapter/Region: MWSOC
Location: Laramie, WY
Vehicle:
2010 LR WRX
MPS powered.

Default

battery tender or something similar, you lose some performance by doing so (vishnu reset can correct this)
drewvdw is offline   Reply With Quote
Old 08-19-2011, 06:08 PM   #16
the suicidal eggroll
Scooby Guru
 
Member#: 51961
Join Date: Jan 2004
Chapter/Region: RMIC
Location: Broomfield, CO
Vehicle:
2005 STi
2012 WRX

Default

Quote:
Originally Posted by fredtga View Post
so, let's say i have a subaru that i'm using only for about 2-3 times a month... track day, rally event you name it, but it is not daily driver...

is it bad to disconnect the battery every time i have it parked ? the battery is a small one and if i leave it connected on the car for about a week, it would barely rotate the engine for start...
You could disconnect it, just remember that your car will never be operating properly, since you'll be eternally driving in "learning" mode with reduced timing.

The better option would probably be to just hook it up to a trickle charger every couple of days to keep it full.
the suicidal eggroll is offline   Reply With Quote
Old 08-19-2011, 09:49 PM   #17
Matt08WRX
Scooby Specialist
 
Member#: 169656
Join Date: Jan 2008
Chapter/Region: NWIC
Location: Scarysville, WA
Vehicle:
2008 WRX 4DR
SSM 331hp/362tq MPS tune

Default

brb going to reset ecu

Great post
Matt08WRX is offline   Reply With Quote
Old 08-20-2011, 02:29 AM   #18
drewvdw
Scooby Guru
 
Member#: 255776
Join Date: Aug 2010
Chapter/Region: MWSOC
Location: Laramie, WY
Vehicle:
2010 LR WRX
MPS powered.

Default

^^^i actually did just reset my ecu...stupid tiny wastegate i can't wait until i can get my ewg on and tuned, so far off though need intercooler, fuel pump, and injectors...
drewvdw is offline   Reply With Quote
Old 08-20-2011, 12:18 PM   #19
cmiovino
Scooby Guru
 
Member#: 134005
Join Date: Dec 2006
Chapter/Region: MAIC
Location: Pittsburgh, PA
Vehicle:
2004 WRX Premium
PSM

Default

I agree with this. I haven't reset my ECU in 2 years since I got the car.
cmiovino is offline   Reply With Quote
Old 08-20-2011, 01:16 PM   #20
vision.dynamix
Scooby Guru
 
Member#: 139955
Join Date: Feb 2007
Chapter/Region: NESIC
Location: Boston
Vehicle:
2015 Subaru STI
Black, like my soul.

Default

Quote:
Originally Posted by Raptor89 View Post
What about a reset after having to unplug the MAF to change the passenger blinker bulb, which causes the CEL and TCS lights to illuminate, and the Cruise Control to blink and not work? Obviously there's nothing wrong (other than the common faulty blinker bulb), as the car had less than 3,000 miles on it. Is a reset in that situation okay?
Did you try to start the car with the MAF unplugged? If so, reset.

Otherwise..umm..unplugging the MAF while the car is off shouldnt throw a CEL.
vision.dynamix is offline   Reply With Quote
Old 08-20-2011, 01:50 PM   #21
SilvrBullit
Scooby Newbie
 
Member#: 288937
Join Date: Jul 2011
Chapter/Region: MWSOC
Location: Milwaukee WI
Vehicle:
2007 WRX TR

Default

I don't understand why a person would assume that this would help solve anything. Seems to do more bad than good
SilvrBullit is offline   Reply With Quote
Old 08-20-2011, 01:52 PM   #22
vision.dynamix
Scooby Guru
 
Member#: 139955
Join Date: Feb 2007
Chapter/Region: NESIC
Location: Boston
Vehicle:
2015 Subaru STI
Black, like my soul.

Default

Quote:
Originally Posted by SilvrBullit View Post
I don't understand why a person would assume that this would help solve anything. Seems to do more bad than good
This applies for at least half of the "advice" spewed around here..
vision.dynamix is offline   Reply With Quote
Old 08-20-2011, 09:59 PM   #23
Raptor89
Scooby Newbie
 
Member#: 285405
Join Date: Jun 2011
Chapter/Region: MAIC
Location: Pittsburgh, PA
Vehicle:
2013 WRX Hatch
WRB

Default

Quote:
Originally Posted by the suicidal eggroll View Post
I've unplugged my MAF many times for one reason or another, and it's never set off a CEL (it will if the engine is running at the time, but it shouldn't make any difference if the key is off). Is this a quirk in the newer ECUs?
Quote:
Originally Posted by vision.dynamix View Post
Did you try to start the car with the MAF unplugged? If so, reset.

Otherwise..umm..unplugging the MAF while the car is off shouldnt throw a CEL.
Now that I think back, I did turn the key on while everything was still detached to test the turn signal and make sure it was fixed and stopped blinking fast...that must've been it. Next time I do anything I'll make sure to leave everything off until I am 100% done. Thanks for the replies!
Raptor89 is offline   Reply With Quote
Old 06-13-2013, 12:46 PM   #24
DieselOx
Scooby Newbie
 
Member#: 334906
Join Date: Oct 2012
Default

Quote:
Originally Posted by the suicidal eggroll View Post



Resetting the ECU is NEVER a valid response to a problem. It will never fix the problem, it will never give you insight into the problem, it will do NOTHING but hide the problem for a few miles before it comes right back, or it could even make the problem much worse than it was before.

There are VERY FEW situations in which resetting the ECU could be considered a logical move. These include:
1) AFTER tracking down, and FIXING a problem with your car (IE: bad O2 sensor, vacuum leak, etc), it's a good idea to reset the ECU to clear all of the learned parameters (which it learned while there was a problem) so that it can start from scratch.
2) After changing the octane of the fuel your car is running, either higher or lower. If you're raising the octane, resetting the ECU will clear out the timing changes the ECU had to make to compensate for the low octane, and allow you to take advantage of the higher octane sooner. If you're lowering the octane, resetting the ECU will put it into an active knock learning mode, which will let it adjust for knock quicker than if you just left the ECU alone. Note that if you're lowering the octane, do NOT, under ANY circumstances, perform the "vishnu" trick after resetting the ECU.
3) After making a major part change on your car and flashing a new tune to suit. Now most tuning methods will reset all of the learned parameters when you flash the new map on the ECU anyway, so in this case, the reset is already taken care of for you.

There might be a couple others, but not many.
NEVER is a strong word.

4) If you drove like a grandma for the first 100 miles in a new OB, and the ECM then can't handle how you drive after that.

I reset mine (actually a recall reflashed it), and my stumbling idle and throttle dead zone was GONE immediately. I drove like I stole it for the next 100 miles, it's been great for the last 10k miles.

Anyway, what I'm really looking for is confirmation that the ECM in Gen4 OB's, both CVT and manual transmissions, have some learning of driver's habits, fuel trim, timing, anything. There's a lot of talk all over the place, but I can't find any documentation. Maybe if you Impreza folks have documentation for this, it could lead to OB documentation.

Just grasping at straws here, been all over the OB forums looking for stuff about it.

Thanks.
DieselOx is offline   Reply With Quote
Old 06-13-2013, 01:02 PM   #25
Jack
Add Lightness
Moderator
 
Member#: 13699
Join Date: Dec 2001
Chapter/Region: NESIC
Location: Hopkinton, MA
Vehicle:
2007 Lotus Elise
(From General)

Default

I reset my ECU because a police car was following me. It worked because when I got done with the reset, the police car was no longer following me.
Jack is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
You know how your lights blink on and off when you reset your ecu? eurojax Off-Topic 7 01-17-2006 08:15 AM
Installing Intake, did you reset your ECU? BLCK DVL Factory 2.0L Turbo Powertrain 4 07-08-2002 12:06 PM
Why reset your ECU when not doing mods? I am b Factory 2.0L Turbo Powertrain 4 02-26-2002 05:10 PM
How do you reset your ECU IcedOutRS Newbies & FAQs 10 03-27-2001 04:41 PM
How often do you reset your ECU? Gambit Normally Aspirated Powertrain 17 10-26-2000 02:57 PM


All times are GMT -4. The time now is 11:48 PM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2014 Axivo Inc.
Copyright ©1999 - 2014, North American Subaru Impreza Owners Club, Inc.