This weekend I pulled my '05 Cooper S out of the garage to work on my KTM. I rolled down the windows , opened the roof and boot lid and cranked up the music for about 4 hours while I worked on the bike. I guess I turned the key on one to many clicks, the lights were on and it ran my battery down. I took the battery out and put it on the charger for a few hours, till the window turned green telling me that it had a full charge. I put the battery back in, went for a drive and immediately noticed that my MINI ran much better. I thought it was running a little sluggish lately, but it does have 53K miles, it needs the air filter cleaned and my tires are getting a little thin on the tread, so I didn't really think much about it. Where I really notice the difference is when I drive in the canyons and heal and toe. Before it was really sluggish and I had to give the throttle a really hard poke to get a good blip between shifts. Now I don't have to, it's super easy to get a good blip now. I even noticed that my Borla Comp exhaust pops louder when I let off the gas.

So what happed when I unhooked the battery and hooked it back up? Does it reset the ECU. I have read the the ECU learns and I have also read that it doesnt. So what the deal?

 

Yes it will reset the ECU. It will then re-learn as you drive it.

 

That's what I thought. But I have read where people swear that is not the case, that the ECU can't learn.

 

It does learn, so teach it to enjoy a life where you floor it all the time and run to redline from each stoplight.

 

Oh, I drive the crap out of this car and have a lot of fun doing it. I am really surprised I haven't gotten a ticket yet. Although I have been pulled over twice. This car is just fun to drive, everytime I drive it!

 

If you have an OEM HK Stereo, you don't have to use the car key to listen to the radio ? Just push the on button a few times with key out of ignition......Radio will stay on for 30 mins and automatically turn off. Then just push on button again for another 30....

 

I do that a sometimes. But mine only stays on for 15 minutes. So I don't do it if I'll be in the garage for a long time.

 

Ours is 15 minutes too. The kids love it because they can get in the car (in the garage) and start listening to their tunes while I'm still running around getting ready. It's also a safer way to leave a kid alone in the car while in the parking lot since you don't need to leave the key. (and, no, these are not little kids--all 12+)

 

Its known in BMW circles that you can reset the ecu by unhooking the battery and connecting the pos/neg battery cables together for about 15 -20 min. to drain all residual energy from the system. The ecu then relearns your driving style and performs accordingly. I don't know if this works on all cars or just BMW-related ones.

 

I also heard you could reset the ECU by disconnect of the battery.
What is the downside, other than resetting the clock and the radio??
thanks
boxcars

 

The downside is that the car may not run so good until it relearns what is necessary in terms of how much fuel to deliver base on the amount of air present; the reason the system learns is to compensate for worn parts that affect the air/fuel ratio as the engine and sensors age.

For example, as the fuel pump ages or develops restrictions in the plumbing the car would tend to run a little leaner than when it was new, so the ECU detects this and commands the injector to remain open another Milli-second or so to maintain the same amount of fuel flow as when the car was new.

If you would like to see what was learned just look at the fuel trim value with the scan tool; specifically the LTFT (long term fuel trim) at idle and then at varying load conditions.

The LTFT value was at 0% when the car was new. You may find the value to be either a positive value or a negative value. A positive value indicates that the ECM has learned that more fuel is needed to maintain a 14.7:1 ratio.

At this ratio, the fuel is completely consumed and pollution is held at a minimum. If the value is negative then the ECU has learned that the engine is being over fueled and a shorter on-time for the injector is required.

The o2 sensor is responsible telling the ECU whats going on. If the trims are between -10/+10 then all is well and considered normal. Outside of this range is an indication of a concern!

Disconnecting the battery will reset the LTFT to 0%, which may cause the car to idle poorly since it already learned that another value would be better.

If repairs are made e.g. vacuum leak, new injectors, pump, o2 or any other sensor that has influence of the air fuel ratio then reset the ECU.

This will effectively wipe the slate clean and allow the ECU to adapt to the repairs faster. If the ECU is not reset it will continue to use the old values which may no longer be appropriate after the repairs, although it will eventually adapt over time. It is always learning. When things get bad enough and the ECU reaches a limit on the fuel trims (+/- 25%) it cannot compensate anymore and something will likely have to be replace.


The ECU does not learn driving styles, this is more a function of the transmission on automatic cars.

 

Frenchie,
that was a great detailed answer,
thank you so much!!
boxcars