Disconnecting the battery

[Bobby Dazzler]

I'm tempted to disconnect the battery to clear adaption settings, but I remember reading that disconnecting or reconnecting in the wrong way can cause problems, like blown SAMs.

So what's the 'right' way of doing it?

 

[gazz]

What adaptations are you trying to reset??

The gearbox can be done by switching to pos 2, hold throttle full on for 20 secs, then switch off ignition, then release pedal. Wait 30 secs then start as normal. The "right" way is with Star machine. Wait 'till May and Olly or I can do it for you if you like.

What sort of problem do you have, anyway??

 

[recycled]

edit

 

[Bobby Dazzler]

What adaptations are you trying to reset??

The gearbox can be done by switching to pos 2, hold throttle full on for 20 secs, then switch off ignition, then release pedal. Wait 30 secs then start as normal. The "right" way is with Star machine. Wait 'till May and Olly or I can do it for you if you like.

I was thinking of trying to reset everything, to return to a clean sheet as it were.

I've done the reset you describe several times, and to be fair it really does sharpen response for a short while, and curiously improves gear shifts and appears to ease the 1500 rpm jerk which is thought to be the torque converter engaging.

When I first came across it, the process was described as clearing gearbox adaptive settings but I've read suggestions that it actually resets the 'throttle body' somehow, and linked to the drive by wire settings.

I'd started to wonder whether the jerk might be related to the throttle body and not the torque converter, and it seems the same thing has been suggested on a US forum.

I read on a US forum that if you don't have access to STAR then disconnecting the battery for an hour or so clears all adaptive settings, and has a longer lasting effect.

So for now it's just for curious experimentation.

 

[johnsco]

remove positive first, then negative

connect back negative, then positive

Having disconnected the positive - Surely that's enough.
There is no need to disconnect the negative, as the battery is no longer in circuit.

Just disconnect the positive.
Wait sufficient time.
Then reconnect.

Cheers
Johnsco

 

[jaymanek]

dont let your spanner touch the body of the car whilst undoing the positive... otherwise it will cut your lovely versace ring in half and you will go flying across the garage..

 

[Number_Cruncher]

Yes, post #3 has it backwards.

It's *much* safer to disconnect the negative first, and re-connect it last.

 

[markmifsud]

Yes, post #3 has it backwards.

It's *much* safer to disconnect the negative first, and re-connect it last.

I was going to say this also, as if you disconnect the negative first, then you cant short anything out with a spanner, and then if you do have to remove the battery, its now 100% safe to throw the spanner at the Positive post

 

[recycled]

Yes, post #3 has it backwards.

It's *much* safer to disconnect the negative first, and re-connect it last.

Please do not ever try this. As soon as you tough the negative with a spanner sparks would fly. always disconnect positive first if you do not want to start a battery fire.
Its in the handbook

 

[recycled]

Having disconnected the positive - Surely that's enough.
There is no need to disconnect the negative, as the battery is no longer in circuit.

Just disconnect the positive.
Wait sufficient time.
Then reconnect.

Cheers
Johnsco

thought he wanted to take the whole battery out like i had to last night after leaving the internal light on for 2 days

 

[Number_Cruncher]

>>As soon as you tough the negative with a spanner sparks would fly.

I'm sorry, but, this is back to front, and is dangerous advice.

While everything is connected, it's the positive terminal (on any modern negative earth car) that's dangerous.

While your spanner is on the negative terminal, there's no potential difference between the spanner and all of the metalwork and bodywork on the vehicle.

On the other hand, if your spanner is on the positive terminal, there's bettery voltage between your spanner, and any of the car's metalwork - one touch, and sparks will fly, if the battery has been gassing, it could explode.

The safe way to do this, is to disconnect the negative first, and re-connect it last.

 

[recycled]

>>As soon as you tough the negative with a spanner sparks would fly.

I'm sorry, but, this is back to front, and is dangerous advice.

While everything is connected, it's the positive terminal (on any modern negative earth car) that's dangerous.

While your spanner is on the negative terminal, there's no potential difference between the spanner and all of the metalwork and bodywork on the vehicle.

On the other hand, if your spanner is on the positive terminal, there's bettery voltage between your spanner, and any of the car's metalwork - one touch, and sparks will fly, if the battery has been gassing, it could explode.

The safe way to do this, is to disconnect the negative first, and re-connect it last.

Ermm can i ask if you have disconnected your car battery before as i had to do mine last night.
Can i also ask if you have a handbook and have read what it says it it?

If you connect the positive in first, as you try to connect the negative last, it would continue to spark everytime it comes into contact with the battery terminal until you struggle through the sparks to stick the terminal on the pin.Since the +ve is already in, the negative will start to complete a circuit before you can even screw it in.

 

[Number_Cruncher]

I've replaced hundreds of batteries, and disconnected and reconnected thousands. Working on cars used to be my job.

Unless the manual you're reading is for a Morris Minor or some other ancient relic, it will (or at least should!) say to disconnect the negative terminal first, and reconnect it last.

Please, could you scan in and post the page of your manual? It's seriously dubious advice!

I've just checked a Haynes manual I have for my W124, which says to disconnect the negative first, and reconnect the negative last.

Whichever order you make the connections in, there will be some slight sparking from the battery as the car's circuits begin to draw current from the battery - that's completely unavoidable, and is quite a low power event.

The connection order I've been writing avoids a *major* firework display where you can put a direct short across the battery possibly drawing the full battery power!

 

[ceejay]

Dangerously wrong advice!

Ermm can i ask if you have disconnected your car battery before as i had to do mine last night.
Can i also ask if you have a handbook and have read what it says it it?

If you connect the positive in first, as you try to connect the negative last, it would continue to spark everytime it comes into contact with the battery terminal until you struggle through the sparks to stick the terminal on the pin.Since the +ve is already in, the negative will start to complete a circuit before you can even screw it in.

Sorry Recycled, but as the two other posters who have already corrected you have said, your advice is 100% incorrect and dangerous. If the spanner slips and shorts out the positive to ground whilst the negative is connected you can get a lot more than just small spark. Always disconnect negative first and re-connect last. Whichever terminal you connect second, this will then complete the circuit and may spark, it makes no difference if this is + or -.

 

[stevesey]

If you connect the positive in first, as you try to connect the negative last, it would continue to spark everytime it domes into contact with the battery terminal until you struggle through the sparks to stick the terminal on the pin since the +ve is already in the negative will start to complete a circuit before you can even screw it in.

Not sure where all this sparking is coming from? The only sparking you will get is as you shove the second terminal on* - whichever order you do it in (and only a few small sparks as there aren't should be any heavy duty consumers turned on). Tightening the bolts should not cause any sparks - unless you are working on the +ve with the -ve still connected and short the terminal +ve to the body with your spanner. Which is why every manual I have ever read says to disconnect the -ve first - although to be honest I rarely do it that way around.

*Unless one of your terminals is very loose.

 

[recycled]

please where are all those who have he c class manuals here page 114 can you all speak up. this guys are making me laugh my head off.
I do not have a scanner.
As i had to do this last night i can only stare in amazement.
And my car still works

 

[recycled]

Sorry Recycled, but as the two other posters who have already corrected you have said, your advice is 100% incorrect and dangerous. If the spanner slips and shorts out the positive to ground whilst the negative is connected you can get a lot more than just small spark. Always disconnect negative first and re-connect last. Whichever terminal you connect second, this will then complete the circuit and may spark, it makes no difference if this is + or -.

your advice is what cause electrical fires in cars i am sorry and burns up ECU's. perfect way to mess up your warranty 100%

 

[Bobby Dazzler]

So disconnect negative first, and reconnect negative last.

How about thoughts regarding damage to SAM, ECU, etc - as this is what would concern me most?

 

[recycled]

bobby have you got a handbook or not? it will explain it better in there and good luck however you want to do it.
I will strictly follow manufacturers instructions which is in my book

 

[stevesey]

please where are all those who have he c class manuals here page 114 can you all speak up. this guys are making me laugh my head off.
I do not have a scanner.
As i had to do this last night i can only stare in amazement.
And my car still works

Page 71 in mine (202 facelift, exterior section).

Disconnect negative terminal first, then the positive

QED.

Won't cause a problem doing it the other way around - just not as safe if you slip with the spanner and short +ve to bodywork.