Trouble Resetting Computer

[axgutt]

I got a CEL on my 95 Legacy Wagon (2.2, MT), and I'm having trouble resetting the computer (which is the first thing I usually try when I get a CEL). I disconnected the negative terminal before heading out of town for a couple of days, and reconnected it when I got back. Started it up without touching the gas, expecting it to do that thing where the RPMs go up and down for a little bit, but it just started idling normally (with CEL on).

 

It seems like sometimes I can reset it by disconnecting the battery, and sometimes not. Is there some specific sequence I should be following?

['84 Flat-Four]

unhook the positive, leave unhooked for 45min or so, then re-connect and you good-to-go.

[illanrob]

I tried to reset the computer on my 93 Legacy 5spd by disconnecting the positive battery terminal and waiting 1hr. Seemed OK that evening, but did not work the next day. Drove back home after stalling twice in idle at 100rpm and does not hover at about 1200rpm between shifts, but noticed that the idle was back at the normal 500rpms when the engine warmed up by the time I got home.

 

Reset the engine computer per the shop manual under dash connections the following evening, no engine error codes recorded from the low idle engine stall. The idle worked OK that evening. Next day ran the car cautiously within the neighborhood and verified that idle was nomal 400-500rpms during the entire start to warm up period. Got to work only 5 mins late.

 

The day before the car had the negative terminal disconnected while removing and replacing the starter, then it could not hold idle at 500 rpms even when engine warm or so and engine would stall in neutral or between shifts.

Edited December 1, 2010 by illanrob

[johnceggleston]

removing the battery cable should work, if you leave it off long enough.

[idosubaru]

It seems like sometimes I can reset it by disconnecting the battery, and sometimes not. Is there some specific sequence I should be following?

have you tried fixing whatever is causing the CEL instead of trying to clear it every time?

 

it's quite normal for a CEL to be triggered immediately some times and then take awhile other times. so it just sounds like you're clearing the code and it's immediately reappearing again and sometimes it's not. sounds totally normal, they do the exact same thing even with a 4 digit OBDII scan tools.

[1-3-2-4]

I tried to reset the computer on my 93 Legacy 5spd by disconnecting the positive battery terminal and waiting 1hr. Seemed OK that evening, but did not work the next day. Drove back home after stalling twice in idle at 100rpm and does not hover at about 1200rpm between shifts, but noticed that the idle was back at the normal 500rpms when the engine warmed up by the time I got home. Will try to reset the engine computer per the shop manual under dash connections this evening.

 

The day before the car had the negative terminal disconnected while removing and replacing the starter, then it could not hold idle at 500 rpms even when engine warm or so and engine would stall in neutral or between shifts.

 

I have the same year and same 5 MT like you first of all the car will not run at 100 RPMS and it's possible it will run on 500 rpms albeit roughly.

 

It sounds like what you are saying is you are trying to get rid of the CEL but unhooking the battery cable for 48 hours (unneeded) is doing no good...

 

How about you check what is causing the code? I invested in a code reading that shows a description of the code and meaning best $65 I've spent.

[illanrob]

The trouble with running the 93 Legacy 5spd started when the negative battery cable was disconnected while cleaning the starter solenoid contacts, solenoid would click but starter motor did not run. The Engine Computer still knew how to keep the engine in fast idle 1200rpm during the first minute or so but did not know how to set the idle after that and the car would stall repeatedly.

 

The disconnect the positive battery cable for 1 hr did some good, idle OK 1st minute, not good next 2 mins, and OK thereafter when engine warm.

 

The reset the computer with the under dash green and black connectors procedure gave the best results, idle OK 1st minute, idle OK next 2 mins, and OK thereafter when engine warm.

 

No Computer Error Light codes were present throughout these events.

[1-3-2-4]

I'm friken lost.. are you saying it ran better with the Green and black connections under the dash disconnected? If so those are not meant to be plugged in they are for reading codes.

[illanrob]

I'm friken lost.. are you saying it ran better with the Green and black connections under the dash disconnected? If so those are not meant to be plugged in they are for reading codes.

 

No, the Green and Black connections under the dash are primarily to read and clear codes, but also has some role to reset the computer since it requires throttle motion and driving the car to complete the reset procedure.

 

So while the disconnect the positive battery terminal has some reset effect, the Green and Black connections has some other reset effects as well. Both effects apply to idle rpm control.

 

I have never tried the positive battery terminal to reset the computer until two days ago with poor results and have allways used the Green and Black connections under the dash with better results.

 

Thanks for your interst and help.

[nipper]

Why hasn't the trouble code been read or did i miss that part? You are blaming the ECU and the car when it is doing exactly what it is supposed to do.

[illanrob]

Why hasn't the trouble code been read or did i miss that part? You are blaming the ECU and the car when it is doing exactly what it is supposed to do.

 

There was no error code to begin with, the problem was on how to reset the engine computer (ECU) after the battery has been disconnected, so that the idle rpms would be high enough to prevent the engine from stalling. Apparently this 93 Legacy L 5spd has had issues with engine idle where the ECU forgets how to control the idle valve post initial fast idle.

 

Idle rpms are now normal, drops to 1200rpms between shifts for 1 sec then gracefully to 500rpms in 3 secs or so.

[nipper]

Why hasn't the trouble code been read or did i miss that part? You are blaming the ECU and the car when it is doing exactly what it is supposed to do.

 

There was no error code to begin with, the problem was on how to reset the engine computer (ECU) after the battery has been disconnected, so that the idle rpms would be high enough to prevent the engine from stalling. Apparently this 93 Legacy L 5spd has had issues with engine idle where the ECU forgets how to control the idle valve post initial fast idle.

 

Idle rpms are now normal, drops to 1200rpms between shifts for 1 sec then gracefully to 500rpms in 3 secs or so.

 

 

Illanrob, i was referring to the original post, not yours. If iI was referring to yours I would have quoted it . You are also OBDI not OBDII which is a different beast.

 

 

Original post from Axgutt

 

I got a CEL on my 95 Legacy Wagon (2.2, MT), and I'm having trouble resetting the computer (which is the first thing I usually try when I get a CEL). I disconnected the negative terminal before heading out of town for a couple of days, and reconnected it when I got back. Started it up without touching the gas, expecting it to do that thing where the RPMs go up and down for a little bit, but it just started idling normally (with CEL on).

 

It seems like sometimes I can reset it by disconnecting the battery, and sometimes not. Is there some specific sequence I should be following?

 

And we are still waiting for the trouble code.