Is there a difference between clearing codes and disconnecting the battery?

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WallyWest

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Got a CEL, O2 sensor code, so I have both upstream sensors ordered. Which reminded me of this question.

I have a OBD2 reader that can clear codes, but does that accomplish the same thing as cutting power and wiping memory? I figure with replacing those sensors I probably want to do the latter, force it to relearn from scratch.

Crazy thing is a few months ago I almost ordered new O2 sensors just as a preventative maintenance thing. Kinda forgot about it, and then bam, takes a crap. It had been a little hard to start sometimes, and the other day it cranked for a good 10 seconds before finally starting up. I was thinking fuel pump, but then yesterday fired it up and immediately knew something was wrong, running really rough. Then saw the CEL. Good times, at least it's something easy.
 
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Mark at @Wranglerfix knows the answer.

if it’s P0431 that is downstream Bank 2- don’t rule out the precats- check for holes and leaks -
 
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I would think disconnecting the battery would also clear any adaptations like long term fuel trims, where just clearing dtc's wouldn't. But I'm spit balling a little bit.
 
freedom_in_4low said:
I would think disconnecting the battery would also clear any adaptations like long term fuel trims, where just clearing dtc's wouldn't. But I'm spit balling a little bit.
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I was reading the same thing and it seems like if you leave them unhooked long enough you can clear the adaptive learning- There’s a good bit of debate But some guy that was an automotive engineer got home one of the forums and was pretty definitive about some things
 
WallyWest said:
Got a CEL, O2 sensor code, so I have both upstream sensors ordered. Which reminded me of this question.

I have a OBD2 reader that can clear codes, but does that accomplish the same thing as cutting power and wiping memory? I figure with replacing those sensors I probably want to do the latter, force it to relearn from scratch.

Crazy thing is a few months ago I almost ordered new O2 sensors just as a preventative maintenance thing. Kinda forgot about it, and then bam, takes a crap. It had been a little hard to start sometimes, and the other day it cranked for a good 10 seconds before finally starting up. I was thinking fuel pump, but then yesterday fired it up and immediately knew something was wrong, running really rough. Then saw the CEL. Good times, at least it's something easy.
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It does the same thing. Now, if you leave it disconnected overnight or take the positive battery cable and touch it to the negative for 30+ seconds it drains the memory and upon re-start the computer has to re-learn. Anytime you change sensors you should do this. First and second start may be rough as it learns, but it will smooth out.
 
Ok, sounds like I should pull the battery cable then.

The code is for Bank 2, sensor 1. So I'm going to replace both upstream sensors. I typically don't worry about downstream unless they throw a code.
 
Or go to an auto parts store, borrow their reader, and clear the code. Or get a $20 ODB2 transmitter and download the Torque app to do the same.
 
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What about stored codes? I had to take my truck, (Mitsubishi Raider, which is a Dodge Dakota with different sheet metal) to get a Check Engine Light looked at. It turned out that it was only a P0456, Small Evap Leak. However, when the mechanic read the codes, it had a list of several codes which were old. Apparently the PCM was holding old codes, even after replacing the battery, which of course means disconnecting the battery, it still stored the codes. I don't know if our PCMs do this, but it might be considered.
 
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