Disconnecting Battery, clearing ecu values and adaptions

[xman]

1.2htp 70ps BZG engine 2009

Does anyone definitely know if disconnecting the battery actually resets the ecu learning values, adaptions or otherwise? Would 10 minutes be sufficient? Unfortunately I dont have canbus vcds.

I want to reset the ecu as daughter has on a number of occasions been affected by the engine racing/being stuck at 4000rpm for several seconds before it recovering on its own slowly over the next few seconds, this happens after been travelling fast at motorway speeds for a prolonged period and then slowing down and releasing clutch. Its not the accelerator stuck. I've seen this happen on our old mk1 htp too a couple of times.

Edited 6 April, 2015 by xman

[Breezy_Pete]

I doubt that disconnecting the battery has any effect on the engine ECU on these. Last time I trawled through a wiring diagram for our AZQ I couldn't find any permanent 12V connections, so I don't see it making any odds.

[PhilTheGeek]

Sounds like you might have an intermittent sensor fault. Find yourself a local VCDS owning forum member and get an error log pull.

[Jabozuma]

Disconnect the battery for 30 mins and all stored "learned" ECU values will be erased.

[xman]

OK, I think Jabozuma may have the best answer, I finally dug out the radio manual and ascertained that the ECU stores and automatically recodes the radio so no code is needed when the battery is disconnected (code only necessary when moving radio to new vehicle/ecu on first time use).

 

I only left the battery disconnected for just over 10 minutes as daughter was in a rush.  Wont get the opportunity to try again for several months as she lives a long way away and doesnt always come by car. The "racing engine" symptom however didnt reoccur on the 400 mile return journey. So far so good.

[Jabozuma]

Looks like 10 mins was enough

The Golden IT Fix works wherever computers are involved, switch off and on again 

[GeneralPurpose]

If the 1.2htp has a CAN bus, then just to be pedantic, it's 31 minutes you must disconnect the battery for. The CAN bus/ecu stores everything for exactly 30 mins. After that you may even need to get the radio code from your dealer. But hope your daughter doesn't get another recurrence of the issue. If she does it's more likely not a relearn that it needs, but some further investigation relating to TPS and some other sensors, which as jabo is saying, could likely be throwing up an intermittent fault. Good luck mate!

[Breezy_Pete]

I'm still confused.

Do these (engine) ECUs have a permanent 12V connection, but I just can't find it on any diagrams I've seen? Otherwise how does disconnecting the battery look any different to the engine ECU than switching off the ignition?

 

If there isn't a permanent 12V, then the only way I can see that battery disconnection could erase (engine, learned) data is if the data isn't stored locally, inside the engine ECU, but centrally, perhaps where the CAN 'headquarters' is? (onboard supply control unit?, which does have perm 12V), and passed into the engine ECU each time it is powered up, or the data requested?

 

Heeeelp?

[Jabozuma]

If any part of can-bus has power all of the can-bus has power the way I understand it as it is a "ring system".

ECU must have a small capacitor supplying voltage to volatile memory chips holding "learned" data.

[xman]

Adaption data, radio code, trim/learning data etc probably all stored in non volatile flash memory nowadays. Canbus being timestamp aware, there will no doubt be an rtc chip somwhere in the ecu or more likely instrument cluster with a large cap to keep it going a long time without main power. The timeout, if it is 30 mins or not, will be to ensure a clean reset of the entire system before that backup cap gives out. Probably a legacy thing before flash existed.

Edited 9 April, 2015 by xman

[Breezy_Pete]

Adaption data, radio code, trim/learning data etc probably all stored in non volatile flash memory nowadays. Canbus being timestamp aware, there will no doubt be an rtc chip somwhere in the ecu or more likely instrument cluster with a large cap to keep it going a long time without main power. The timeout, if it is 30 mins or not, will be to ensure a clean reset of the entire system before that backup cap gives out. Probably a legacy thing before flash existed.

That bit I've bolded is exactly what I'd expect, which is why I doubt that the (engine) ECU needs a permanent 12V, if that's where this stuff is stored, and why I doubt(ed) that these items are erased by battery disconnect (for any amount of time). CANbus is a mystery to me, but I don't think connection to the data lines alone would make an engine ECU be 'aware'/'active' if the rest of it doesn't have power to energise the chips that deal with CAN??

[GeneralPurpose]

Basically, the car has 'KAM' (Keep alive memory) which remembers the day to day stuff for 30 mins after battery disconnection. It's only powered by capacitor. Once exhausted it 'forgets' stuff including some engine running 'learned' parameters. Although all the important stuff is hardwired into the ecu, but alas not the radio code. Electric windows need to be reset too anytime the battery is disconnected for any amount of time.  

[Fatbloke]

Basically, the car has 'KAM' (Keep alive memory) which remembers the day to day stuff for 30 mins after battery disconnection. It's only powered by capacitor. Once exhausted it 'forgets' stuff including some engine running 'learned' parameters. Although all the important stuff is hardwired into the ecu, but alas not the radio code. Electric windows need to be reset too anytime the battery is disconnected for any amount of time.  

A couple of questions for Mr Estate Man. Is the radio code not stored in the instrument unit? To my other question, if the car (2010 1.2HTP Fabia FL) only does short journeys, is it possible for the ECU to struggle to re-learn values if it currently has bad values learned during problems? Which, if the case, could be corrected by a battery disconnect reset?

[Jabozuma]

Question clearly directed to somebody else so I am speaking without being spoken to

No cluea about radio code. I took battery out a car once, Lupo TDi for whole day to charge it properly and had no problems with radio or anythong else.

ECU has all the maps it needs to work correctly. "Learned values" we are talking about here are correction tables ECU writes values into based on the particualr environment, fuel, oil, altitude, driving style etc.

Knock table, fuel trims, ignition advance. Some fields will never be written on depending on your driving style. If you do not redline your engine those fields at max rpm and load will not have any adjustment written in them.

So the best practice would be to bring the car to the temp and take it through all gears to red line but this is impossible on public roads. Just drive normally and it will be fine