Memory saver

[p0689109]

Has anybody any experience of these gadgets? I was carrying out a service on the daughters-in-law new style Beetle and, whilst browsing the booklets that come with the cars these days, I happened to read about battery changes and they mention using a "memory saver" to stop you losing certain vital memory codes. The obvious one is for the radio but it did mention the fault code history etc. As I run a Tiguan and the battery will not last forever, I thought it might be a good idea to get one of these devices. I have had a scan of the bay of e and all those mentioned there mention that they are for saving the radio code. My question is would that cater for what VW are highlighting or is there a more industrial kind that I should be aiming for?
Any feedback will be useful.

 

[grandads_shed]

if you are just changeing the battery then a 12v battery charger supply connected to the battery terminals will stop it losing the codes

 

[Robotstar5]

I made one from an accessory plug, a diode and a 9 volt battery, just plug into cigar lighter/accessory socket, remembering some cars need ignition position I to turn on socket.

 

[p0689109]

Having just googled it it seems it is a matter of supplying 9v to keep, amongst others, the ECU KAM alive. That is the "Keep Alive Memory" that the ECU saves through use. It caters for the vagaries of the different sensors and their tolerances and apparently your driving techniques. If you lose it the car can appear to not run right as the ECM has reverted back to the basic state tune and has to relearn the package. It also keeps powered the memory of things like the radio, GPS and climate control and even the seat selections on the top models! Very important that bit.
Some of the solutions on you tube include a 9v battery connected to the battery terminals with crocodile clips then the main battery is removed. I would have thought the 12v in the main battery would have backflowed to the 9v one whilst the main battery was still in circuit. Another showed someone using a 12v ac adaptor with a diode soldered into the positive lead to protect against the backflow or two 6v batteries. I suppose it depends how long the battery is going to be disconnected as to what power supply you use. I do not like the idea of a battery charger as its output can be variable. But not being an electrician what do I know!!

 

[Robotstar5]

Some of the solutions on you tube include a 9v battery connected to the battery terminals with crocodile clips then the main battery is removed. I would have thought the 12v in the main battery would have backflowed to the 9v one whilst the main battery was still in circuit.

That's why I fitted a diode on mine, prevents loud bangs!

 

[p0689109]

The aussie doing it seemed to get away with it!

 

[AndyStobbs]

I do diagnostics day in day out. I always use a memory saver where possible. Mine is an EOBD plug type. Works very well. Current limited to 10a so you can't do much with the car while its plugged in and no battery is fitted. People are always bringing cars to me without codes, so its good to keep the power on, especially as 90% of jobs require battery removal.
It also saves from getting that horrible crack on first re-connecting a battery and 1000 capacitors all charge and a dozen actuators get going on a self test.

 

[p0689109]

Yeh, that's the one I am going for the eobd. Many thanks for the inputs lads.