The simplest things……

[Dancake]

Originally Posted by Tannaton

It’s nothing to do with touching the battery cables together.

It does work if you're having issues such as those posted by the OP. Pulling fuses and unplugging certain components with the battery connected or the ignition on can corrupt multiplex systems. Touching the cables together forces the modules to start from scratch the next time they are energised. Providing the software hasn't been corrupted (unlikely), this procedure can be quite effective.

[S60D5-185]

Originally Posted by Familyman 90

You need to be a little careful disconneting/connecting the battery to avoid corrupting or damaging the CEM.

I agree which is why I clearly stated follow the procedure in the handbook.

[Tannaton]

Originally Posted by Dancake

It does work if you're having issues such as those posted by the OP. Pulling fuses and unplugging certain components with the battery connected or the ignition on can corrupt multiplex systems. Touching the cables together forces the modules to start from scratch the next time they are energised. Providing the software hasn't been corrupted (unlikely), this procedure can be quite effective.

Absolute cobblers…

- Software is held in non volatile memory (nvm) in modules and cannot be corrupted or changed by power cycling.

- The suggestion touching the battery + and - cables together whilst the car has no power to force a deeper restart is fanciful. With no power to the car, processors are not running, nothing is monitoring, no heartbeat or communication on the buses, it's a hocus pocus theory

- To the contrary, if there was any residual power in any system after the battery has been disconnected (i.e. a charge stored in large smoothing capacitors on module power supplies), you run a completely unnecessary risk of damaging the electrics by creating a zero ohm short circuit between the supply and ground feeds, which could result in a momentary but significant power surge and a back EMF spike

If you really feel the need to try this suggestion - connect a resistive load between the +ve and -ve terminals such as a tail light or interior light bulb - on a 1980's car (with logic arrays rather than microprocessor controls) it may have occasionally made a difference but not on a modern Volvo.

If you’re still going to challenge me and promote it as a solution - give us a technical explanation as to how it makes any difference…. Find a post on here where someone has corrupted software on a module and it had to be reloaded?

[Dancake]

There's nothing cobblers about it. At no point did I say that software WOULD be corrupted. I mentioned that it was unlikely. What I did say was that multiplex systems can be corrupted, or rather behave in a way that you otherwise wouldn't expect them to when interruptions are introduced. Draining residual power (and we're talking very small amounts here) can and often does fix spurious behaviour in automotive applications. It is something I wouldn't recommend doing on more modern vehicles as there's an increased risk of causing damage to the electrical systems.

[giw12]

Car started just fine this morning and the On Call Service Required message has gone, so all good.

Question though...can anyone explain why the car just decided to start?

It may help to know that I put my Ctek charger on it for a few hours before trying yesterday evening, but personally I would think that's not relevant as the Varta battery is only a couple of months old and I drove 550 miles last Friday.

As ever, thoughts welcome!

[Deebs]

Originally Posted by giw12

Car started just fine this morning and the On Call Service Required message has gone, so all good.

Question though...can anyone explain why the car just decided to start?

It may help to know that I put my Ctek charger on it for a few hours before trying yesterday evening, but personally I would think that's not relevant as the Varta battery is only a couple of months old and I drove 550 miles last Friday.

As ever, thoughts welcome!

My 2004 had some complex electrical issues. It was a combination of some of the fuses losing power in the REM (solved by replacing one of the relays on the pcb) and a bit of corrosion on the main power connections in the engine bay (solved by a good clean up with emery cloth).

My bet is you have the same corrosion causing slightly high resistance. Thus, the ctek gave your battery the extra boost it needed when the battery terminals were loose. Mine struggled to start unless I fully did up the terminals until I got rid of the high resistance. Good news is yours is starting without problems now. So I wouldn’t worry. But if you get problems starting in the future, check the main cables in the engine bay by the fuse box and main earth post. Chances are a good clean and you will be all good again.

[giw12]

Funnily enough……car is currently reporting engine service required, brake assist service required and an anti-skid issue.

Could it all just be grimy connections?