It's not necessary but it's also not a bad idea. Just make sure you're not due for a vehicle inspection in the next week, since the computer will not be "ready" for a scan until it re-learns its operating parameters.

After you perform the reset, all that is needed is for you to drive.

 

"you don't have to" - I agree with that.

"but it's a good idea" - why?

My understanding is that a disconnect might wipe the engine data memory and put the control system into a default mode until new data, including any changes from the new plugs, is accumulated. But any other data based on other engine parameters is also going to be lost. It would seem that it's better to have the ECU accumulate data based on the last information on the whole system and make changes based on one variable rather than start from scratch.

I don't see where disconnecting the battery has any advantage. Might even be a disadvantage.

 

Note I said "not a bad idea" which does not necessarily infer "it's a good idea"

When you disconnect the battery you're only erasing short-term fuel trim and spark tables. The permanent programming of the ECU, i.e. the "base" you speak of, remains in long-term non-volatile memory.

Personally I'm of the opinion that if you do maintenance to "improve" the engine's chance of running at peak efficiency, a reset of the volatile memory is good practice to ensure the computer's fine-tuning of its own running parameters are based on the newer more "ideal" components. These could be spark plugs, a clean MAF sensor, new oxygen sensors, a better flowing exhaust, etc. etc.

That's just my $0.02 though, YMMV.

 

- Clock
- Compass
- Radio Station Pre-sets
- Any owner modifiable features such as seat belt chime options, etc...

DEWFPO

p.s. I didn't disconnect my battery when I changed my spark plugs.

 

thanks for the responses and info. i think i'm just going to leave it connected. thanks again.

 

How exactly do you "perform" the reset on the ecu?

 

It's not necessary. But, if you want to anyway; remove the negative cable for at least 30 seconds then reconnect.

DEWFPO

 

Thank you very much!

 

First year I had my FJ and changed the plugs, I pulled the neg cable. Since then I just change the plugs. Did not notice enough of a difference to bother with resetting the compass, the radio presets, and "normalizing" the power window pinch protection

I also clean the MAF with CRC Mass Air Cleaner, and the throttle body with 3M Throttle Body cleaner

 

Resurrecting an old thread here, but didn't see any resolution on this issue. I changed my oil and right afterwards, the FJ started with the hesitation and stumbling. I did the MAF clean and replaced the k&n with a stock type filter, regapped the plugs (because they were only 6 months old) and I was still getting the stumble. After reading this, I figured why not? Nothing else worked, so I disconnected the negative terminal while I cleaned the MAF once again really well. After it had time to dry, reinstalled everything, reconnected the battery and it fired right up with no hesitation! I'll need to check again today, but it was like night and day last night. Can't say if it was the reset or the MAF cleaning again, but I would guess the reset because I cleaned the MAF well last time. How this helps someone else because it's hard finding troubleshooting threads with resolution.

Thanks,
Matt

 

I have never reset when cleaning the MAF and it always seems to smooth it out immediately. Maybe it's because I wait too long between cleanings but idle seems much smoother and performance more spritely. Last time I cleaned the MAF it was 2-3 years. The difference was so notable I'm doing it once a year now just to be sure.