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disconnecting Negative terminal to clear codes?

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Old 02-07-2012, 09:00 AM   #1
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disconnecting Negative terminal to clear codes?

Is there any reason that disconnecting the negative terminal overnight would NOT clear codes? I have read all over the internet that it takes anywhere from 5 minutes to 8+ hours. Its all anecdote. Then I come across claims that OBDII systems can't be cleared with that method.

I had p0150 and p0151 the O2 sensor codes both for Upstream. I recently replaced them with some Denso sensors from Rockauto. The original sensors were all kinds of nasty so either way it was a good idea to replace them. I did not have a scanner with me so I decided to try the negative terminal. Overnight at around 10 hours or so did not clear the code on my 96. This morning I stopped by O'Reileys and the tech allowed me to "clear my own codes" with the store scanner. so does this mean that our ECMs store codes in permanent memory and not a temporary way that relies on a completed circuit?
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Old 02-07-2012, 09:14 AM   #2
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cleared?

When u disconnect the battery, u are not clearing codes. You are instead resetting the ECU and losing all stored A/F settings. The proper way to clear codes is to use the ECU screw method.

There are some codes that even after removing the negative battery lead will not reset the light. Leaving a sensor disconnected will cause the CEL to illuminate even after immediately removing negative battery terminal or even after resetting the ECU using the screw method.
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Old 02-07-2012, 09:18 AM   #3
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I thought everything pre 5.5 gen you could just unplug the negative terminal to reset SES codes. I have my own scanner now so I use that method. Did you have him check the codes before he cleared them? It could have been a different trouble code than what you have addressed.
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Old 02-07-2012, 09:22 AM   #4
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cleared?

When u disconnect the battery, u are not clearing codes. You are instead resetting the ECU and losing all stored A/F settings. The proper way to clear codes is to use the ECU screw method.

There are some codes that even after removing the negative battery lead will not reset the light. Leaving a sensor disconnected will cause the CEL to illuminate even after immediately removing negative battery terminal or even after resetting the ECU using the screw method.
^^he's on to something
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Old 02-07-2012, 09:33 AM   #5
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makes sense guys, thanks. Yes I read the codes before clearing them out this morning. It was the same exact codes I had before I replaced the sensors. There was nothing new in my system. I'm satisfied that I fixed the right problem just wasn't sure how to get the light to turn off without a scanner. The screw method slipped my mind to check first. Going to print those out from the stickies right now in fact. Light is off as of this morning and hopefully the new sensors will help remap and adjust the A/F settings.
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Old 02-07-2012, 11:15 AM   #6
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IIRC, with o2 sensors you have to reset the ECU using the screw method or complete a few driving cycles to get the CEL off.
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Old 02-07-2012, 02:55 PM   #7
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@cashoit, just curious, how long is a typical drive cycle anyway? I read something on a FSM one time that broke it down into something that looked like breaking in your brakes, but it didn't seem like it was any kind of length that would be useful.
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Old 02-07-2012, 04:43 PM   #8
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IIRC its three drive cycles(that doesn't mean cutting off and starting three times) for the ECU to perform its diagnostics and ensure the problems has been fixed.
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Old 02-07-2012, 09:09 PM   #9
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Yea either reset Ecu or have codes cleared via obd2 scanner. Battery method doesn't work
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Old 02-08-2012, 11:36 AM   #10
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drive cycle can be anywhere from 30 - 100 miles. After 100 miles, no light u good
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Old 02-20-2012, 05:32 PM   #11
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Disconnecting the efi fuse usually turns off CEL's.
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Old 02-20-2012, 11:54 PM   #12
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Is there any reason that disconnecting the negative terminal overnight would NOT clear codes?
I can confirm that disconnecting the negative terminal overnight will absolutely clear codes.
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Old 02-21-2012, 08:28 AM   #13
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I do feel like I fixed my problem though Wizard. Although I disconnected the terminal twice, after replacing the sensors, one time for around 3-4 hours and the second time a full 9 hour over night thing.

Both times the sensor codes stayed in the system. I don't know what was causing them to stay but I cleared them with a scanner and have run the car around 500+ miles on it. My ECU has already readjusted itself and I can definitely feel a quicker throttle response from when I did the repair.

I am not, repeat not calling you out on what you said but it did not clear my codes for whatever reason. /shrug
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Old 02-21-2012, 07:19 PM   #14
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That's strange. I've done this many times on both of my Maximas, and two of my friend's Maximas as well. Now you got me wondering how long it really takes. Maybe 12+ hours is the answer and why it's worked for me in the past.
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Old 02-21-2012, 07:35 PM   #15
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I've read and have been told it takes a minimum of 11+ hours using this method, but fastest ways are by OBDII scanner or screw method.

Didn't cycles depend on the number of times the car is started and turned off, not mileage.
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