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reset check engine light info...

M

meengreen

NAXJA Forum User
Location
New Jersey
What is the cycle time for an on board computer to reset itself, after the battary has been disconected?
I disconected it to clear the check engine light so it would go through inspection. What I didn't know was, it needs a certain cycle to have readings to upload into the computer at DMV. I failed because I had 5 "Can't reads".:confused:
 
meengreen said:
What is the cycle time for an on board computer to reset itself, after the battary has been disconected?
I disconected it to clear the check engine light so it would go through inspection. What I didn't know was, it needs a certain cycle to have readings to upload into the computer at DMV. I failed because I had 5 "Can't reads".:confused:
Click to expand...

What year? As far as I know neither the OBDI nor OBDII needs to reestablish itself before giving a reading. The OBDI will give an extra code (12) for a disconnect within the last 50 cycles, but will give that and the normal 55 immediately after reconnecting. This I know from experience, having cleared codes that way several times on 93 and 95 XJ's. The OBDII should also give readings immediately, but it does need the ignition to be on. I see no other cautions about this in the 99 FSM. I haven't tested this, but I know that a disconnected battery does not trigger any trouble codes or check engine light on a 99.

Perhaps we need to know more about what the check engine light was on for, and how the test was done.
 
Sorry I left out some info. I am at work and try to hurry and post while my machine is running (I am a machinist). My XJ is a 2001, build date is June 16 2000. I don't know if build date is relavant, but I figured I'd throw it in. I went to New Jersey Motor Vehicle Inspection. In the old days they shoved a senser of some kind up the tailpipe and took readings. Now they plug into the onboard computer and let the vehicle itself tell the story.
Well, my check engine light lit up about 2 weeks ago. I have heard the when the light is on, it is an automatic fail. It could have been a missfire or something that's no big deal, and I didn't want to fail automaticly. So I cleared the light by disconecting the battery and got 5 or 6 could not reads. I dissconected it down the street from the DMV. After waiting on a short line it was about 15 minutes between the disconect and the reading. I can scan the readout later when I am at home. Thanks, John.
 
Here is the print out I got from the DMV. Notice the 4 (not 5 or 6:looney: ) "NOT READY"s that have been highlighted.
scan001001.jpg
 
just like you said, on the new vehicles, they just plug a scanner type setup in to see if everything passes. it also detects if you've unplugged your battery. since unplugging the battery is a free simple way to erase your check engine light, they assume that's what you did and automatically fail you. you'll have to get some time behind the wheel with a certain amount of ignition starts (don't remember exactly how many) before they will accept it. so basically the only way to pass the new vehicles is to have a passing vehicle.
 
scorpio_vette said:
just like you said, on the new vehicles, they just plug a scanner type setup in to see if everything passes. it also detects if you've unplugged your battery. since unplugging the battery is a free simple way to erase your check engine light, they assume that's what you did and automatically fail you. you'll have to get some time behind the wheel with a certain amount of ignition starts (don't remember exactly how many) before they will accept it. so basically the only way to pass the new vehicles is to have a passing vehicle.
Click to expand...
That is exactly what I already know. They failed me because of all of the "NOT READY"s that popped up, not because I disconnected the battery.
What I really need to know is how many on-off cycles and/or how many miles before it will give an acurate reading.
 
because the battery was disconnected the ecu is still "learning". on the paper it says that you have 45 days. i think thats plenty of time to get the not readys ready. if you drive you car twice a day to work and back. thats 2 starts a day +extras. so in about 25 days it should be gone. keep in mind that you do not unhook your battery.
 
So what your saying is 50 on-off cycles? I still haven't gotten and exact answer. I appreciate the explanation and what I should and shouldn't do, but I really want to know what the exact answer is.:roll:
 
There may be an EXACT way to do what you want to do but what the DMV checks for is something called an "I/M readiness" test. What the OBD II does is see how many miles you traveled at what speeds, how hot the engine got, how long you idled, how many times the key was turned on and off and how many minutes/hours inbetween etc, etc. Someone may know the EXACT conditions the OBD II uses to decide if it will tell the DMV that its ready, but it actually relies on a lot of different factors.

X2 to 5-90. Your car is trying to tell you something.......Could be something stupid like 'you left the gas cap off' or 'I'm misfiring after 70000 miles on the same plugs' Goto someplace that will read the codes for free
AutoZone, etc......
 
obd2 readiness monitors , http://auteltech.com/images/GS400-manual.pdf ( brief overview )
scroll down to section 2.4 , some are continous monitor ( like a misfire )
others like evaporative emissions take specific drive cycles to be tested ( ready )
theoretically all readiness monitor tests can be completed in 1 day under controlled conditions .

the question remains , why was the light on to begin with ? could have been just a loose gas cap .
some locations will allow 1 stored pxxxx code , as long as it is not current ( cel/mil light on ) .
 
IF you are going to keep the jeep go get an acctron tool, $150 at autozone, eliminates all the guess work and allows you to reset the CEL without disconnecting the battery. I had mine come one one time and disconnecting the battery did not reset it, it finally reset it self after 5 or 6 complete cycles with a cycle being cold to hot to cold again. I never found out what it was and it never came back. The acctron tool comes with a cd with all the codes on it and allows you to scroll thru the codes as it reads. Plugs in right under the dash by your left leg...
 
THANK YOU!! That was a lot of great info, just what I was looking for. I will try to get over to Autozone for a reading, so at least I know what the problem is.
 
I second the motion to buy a scanner. Even the El Cheapo $49 from Harbor Freight Tools works, and will reset the codes. The only "gotcha" with the Harbor Freight one is that it resests the codes automatically, so you have to read the codes right the first time. The one from Auto Zone doesn't reset the codes until you tell it.

A few weeks ago my wife came in and said the check engine light was on, and the coolant was low. Dunno how she figured the coolant was low, but I added some to the overflow bottle (which wasn't empty) and shut the hood. The next day she said the light was still on, so at this point I got out the scanner.

The code was for a "large scale evaporative leak" or something like that. After a few minutes of :huh: , the light bulb went off. I opened that little door on the back and tightened the gas cap. Used the scanner to clear the code, told her to make sure the gas cap clicks when she puts it on, and that was that. :doh:
 
langer1 said:
Harbor Freight has a new one now with a few more bells a whistles.
Click to expand...

No suprise, when the one I got first came out it was around $300, then a few months it was $249, then few months later $200 and a year later it was $150. Commodity now...
 
If I buy one of the scaners from Harbor Frieght or elsewhere, will it work on all vehicles?:confused:
It might be worth getting one if it will work for the vehicles I will own in the future also. If not I will just go to Auto Zone and let them read and clear the codes for me.
 
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