Battery disconnect knob on 575

Not if its left on trickle charge is the usual response

 

Stuart- No, never for me. Use a battery maintainer, like Jimmie said.

 

One reason NOT to use it is that on start up it requires a lengthy idle to reset ECU parameters before you can drive it again.

 

Stuart, I used to be a big fan of using the BDS to save the battery. I have a 1995 456 GT, which is pre-OBDII, the Motronic 2.7 ECU.

All I can say is, the 2.7 ECU seems to have little problem with reset. However, if I had a post-1996 system, I'd avoid the BDS, if possible. I recently did a "reset" on our Jag XJ-8 ECU, after a tranny rebuild, and then had to get the car emissions tested.....it failed, and we had to drive it for about 100 miles before the ECU reset.....

The pre-OBDII cars don't seem to care.... Much... But if it takes 100+ miles for the OBDII to reset, I'd say don't use the BDS on your 575. The relearn process for the ECU is just too involved.

I'm eating crow here.... as someone who said a trickle charger is unnecessary. I now think it's essential if you park the car for more than a week....and have a car made after 1995.....

I'm learning.......as should we all....

Regards.....Mark

 

I turned it off once and never again. It is not worth it. It was running on 6 cylinders and barely moving 'til everyone explained to me the long reset procedure.

+111 Battery tender!!!

 

RTFM (5.5) for basic procedure - there is also a long procedure whose pdf is not to hand but has been recently posted

 

Stuart- There is a complicated run cycle that involves driving, but the simplest procedure is one is this. Assuming the car is cold from sitting at least overnight.

Turn off AC, radio, and any accessories.
Insert key and leave off (0) for 60 seconds.
Turn key to on (II) and leave for 30 seconds.
Turn key to off and wait 30 seconds.
Turn key to on, wait for check ok, and start.
Let idle for 10 minutes with no input whatsoever.
Turn on AC and radio, inserting code if necessary.
Drive gently for 20 minutes.

That should do it and is much simpler than the drive cycle and rationale attached here.
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Stuart- It is there for techs to do work on the car so they do not destroy electrical components while doing so and to prevent problems when replacing the battery.

 

Don't worry about it Stuart. Doubt you'll notice the difference during the Relearn Drive Cycle. My experience was just a pain because my Jag's emissions sticker was expired and had to complete a drive cycle with an expired tag! I had to check the OBDII readiness every time we drove the car and it didn't show "ready" for over 100 miles. Since a cold start was required each time, it took days. If you don't live in a land of smog testing, it wouldn't really matter.

Drive long enough and everything will reset....It's just a pain if you want it to reset right away.

I think Masinari's experience, with a bank shut down, was unusual....

Any time you clear codes, it does the same thing....resets the ECU and requires certain drive cycles to get the ECU "ready" again.... so this is just part of the OBDII system for all USA cars built after 1995.....

But, as said, if you don't have to, the BDS is not the best thing to use to preserve your battery on post-1995 cars.

Me????? I'll continue to use the BDS for storage in my non-OBDII compliant 456 GT.....

Regards..... Mark

 

What happens when you switch off the battery connection and you do not follow the procedure ?
I'm sure that many owners do not know the procedure.

Daniel

 

I must be lucky. have used the BDS many, many times on my 328, 360, 430, 512TR, and 575 and never had an issue. Even on my 575, used routinely and never knew there was a 'procedure". Just switched it on, ran idle for a few minutes and away we went. i wish there was one on my 458. You are dependent on having an outlet nearbuy.

 

Daniel- I have done it on my 575 after my techs did something to the car. Idle may be a little rough initially, may take multiple cycles to get the AC to come on (CAN and ECUs not fully communicating yet), and the car would likely not pass emissions if tested right after turning on. After a few drives, everything is back to normal as the ECUs relearn and CAN connections are normalized.

When necessary, the BDS is useful, but as a routine thing, probably not the best thing for the car and not something you want to do if you have a non-emissions related warning lamp. Can delete codes that are helpful to the techs for diagnosis.

 

on 96+ its best to use a trickle charger. on 95 and lower cars it doenst matter.

ive used the knob many times on 96+ cars and they reset no problem. you do not need to follow that tech bulletin...atleast thats my experience on a bunch of cars...

 

The simple start up procedure and 10 minute idle generally works as well as the drive cycle.

Here is the latest for late model cars when changing the battery. Most of these would be late 7.1.1 and 7.3.2 DMEs.

Also what page 2.02 in the 575M WSM says to do.

The procedure I wrote above combines all I have seen from multiple versions of the self learn cycles.
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I am surprised to hear what most people`s respond; I am on the opposite side of the island here.

I use the main battery shut off knob almost everytime I leave my F-cars longer than one week. So all my F-cars are constanly resetting itself everytime I turn the knob off and on for the past 10 years or more...

Maybe I should change my bad habit to stop using the turn knob, and start to use the battery charger and or conditioner...

Alex

 

I had no idea of this proceedure and have used the BDS many times as I don't have a plug for a trickle charger and thought this was the best way to presverve the battery as I travel quite a bit. After starting on the car does idle poorly then comes good over time.

I'm glad to know this and I'll use it only for longer term non use.

Thanks,

Andrew

 

Indeed no issues at all with 2.7 motronic cars. Turn it back on and go.

On newer models, as discussed it can take a while to adjust the ECU's. A drawback of this is that generally more fuel is used during the learning period than when it's fully aligned. Same is true if critical sensors or parts are replaced, such as an air flow meter. It can take the equivalent of about two tanks of gas for it to relearn such an item (if you let it discover everything by itself).

 

Contrary to other posters, I suggest that you do disconnect the battery knob if you are not using the car for a while. Two reasons: First; if you don't disconnect, you will drain the alarm battery and it won't recharge. Second; the tire pressure senders will go flat and you will get a default code that is a major stinker to get rid of.

 

Alan- Zero for two.