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Old 01-13-2003, 04:38 PM   #1
ciper
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Default CELS, do you clear them or fix the error and they disappear?

Okay, the way Ive understood subarus Check Engine Light scheme was the following.

Error detected, no CEL
Error continues or repeats x times, Cel illuminated
If error was constant for a long time but stopped Cel go's out and code is stored
If error was repeating cel will go out until the error happens again, code is stored

Cel will NOT illuminate if old codes are stored but not currently active

Now I have heard many people talk about "clearing codes" and pulling the battery terminal to turn the CEL off. From all the knowledge I have gained I always knew this to not apply to subaru.

Basically what Im asking is if Im right in the belief that the CEL will illuminate ONLY when the problem is occuring, not afterwards. The only thing CLEARING CODES does is get rid of non active codes currently stored.
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Old 01-13-2003, 06:11 PM   #2
munkis
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basically there two types of codes.

hard faults
and non-hard faults.

a hard fault, is set, it can only be cleared after the problem has been fixed.

ie your maf sensor is on the fritz, the ecu will set a code, if you attempt to disconnect the battery or clear with a scan tool, the code will come right back as soon as you start the car because it is a hard fault.

non-hard faults or intermittent problem, will illumanate the cel when the problem is occuring, if the problem goes away, after a certain number of 'drive cylces' without the ecu seeing the fault again, the code will be stored in memory and the cel will be go out.

when you disconect the battery you will clear the ecus memory in turn clearing all intermittent fault codes stored.

you are correct in that a fault must occur on obdII vehicles IIRC 5 times before the cel is tripped, untill that time the codes will be 'pending' and most scan tools will let you see what codes are pending.

there is more too it, but thats basically how it works. Emmission system codes will trip the cel and it will stay illuminated, untill cleared....like evap codes set due to leaving your car running while filling up.

thats about all I can think of now, im sure jeremy will pop in and maybe be able to correct me if im wrong as my memory isnt great... eheh

Jay McDade
Lincoln/Mercury/Jaguar Tech.
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Old 01-13-2003, 07:01 PM   #3
ciper
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Thank you. So in short disconnecting the battery is not the correct method to turn the CEL off.
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Old 01-13-2003, 07:37 PM   #4
Legacy777
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Quote:
Originally posted by ciper
Thank you. So in short disconnecting the battery is not the correct method to turn the CEL off.
Depending on the type of code......as he said, if it's a non-hard fault. Disconnecting the battery will clear it.

It's probably not the most appropriate way, but it does work for those particular types of codes.

I've done it.......granted OBD1 is slightly different then OBD2.
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Old 01-13-2003, 07:50 PM   #5
Karl
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If you have a CEL, you probably would want to know what it is before you clear it anyway. If you don't have a scan tool of your own, Autozone will pull codes for you.
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Old 01-13-2003, 10:55 PM   #6
munkis
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Quote:
Originally posted by ciper
Thank you. So in short disconnecting the battery is not the correct method to turn the CEL off.
no not the correct method because your clearing the entire ECUs memory including its adaptive stradgey. (over time your ecu will learn, it will learn what type of gas you use, as parts wear it will learn to compansate for that as well, etc etc.)

All this it will have to re-learn, usually giving you bad gas mileage and poor performance untill it re-learns.

will it work yes, is it the best method, no.



Jay
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Old 01-21-2003, 02:29 PM   #7
xzchaos
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How long should it take for the ECU to re-learn? Also, if you were to get a misfire code and left the CEL on while still driving, would this CEL put the ECU into a "safe mode"?
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Old 01-23-2003, 06:20 PM   #8
romoranger
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how or where do you get these scan tools of your own?
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Old 08-06-2005, 07:55 PM   #9
2slofouru
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I've disconnected my battery several times for a few minutes and my codes stay. I have one thing that will cause a code and it's my egr temp sensor. The only reason it causes a cel is because I haven't threaded the 2.5 intake for it yet and it's tied to a cable temporarily. I still have two other codes for my idle control valve and throttle position sensor. Their cels were on because I accidentaly cranked the car with them disconnected. Now that they are connected, the code will not erase from memory. I am going to leave the battery disconnected with the parking light switch on for thirty minutes this time. My ecu is a 1995 OBD1 for a 1.8l. Hope it works.
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Old 08-06-2005, 09:53 PM   #10
2slofouru
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Default 45 minutes did the trick

Yay it worked! This time I left the battery disconnected for about 45 minutes and voila, no more codes. I even drove it for about ten minutes and no cel! When I got home, I checked for any codes and none were stored. Apparently I can't just "disconnect the battery and push the brakes a few times", it takes a little longer (on my model anyway).
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