C70 Cabrio: roof only works on battery power
 

Hi folks,

Bit of an odd one, the roof on our ‘04 C70 has stopped working (up and down) when the engine is running. It only works with the ignition on and using battery power alone...not ideal. The light on the button flashes when pressed whilst the engines running, but no action, so I’m not sure it’s the button or a circuitry issue.

Other than that the roof is perfect and in great original condition.

Thoughts welcome - thanks.

Could it be your battery voltage is too low when the engine is running?

This shouldn't be the case as when the engine is running, the alternator is outputting at around 14 volts and that is what the roof would "see".

It really is a weird one which I'm struggling to find an explanation for.

Regards
John

Do you think it might be a safety thing? People opening up a roof at say 50mph could easily cause that roof to become a sail and either be ripped off causing a hazard of flying debris to other traffic or the sudden drag of that sail could cause the car to swerve.

If this has only happened after a service and they updated the software during that service, i'd suggest this is a very likely option.

However, it would make more sense for the roof to only be operable when the engine is running (so the alternator is charging the battery) but the car is stationary. It may take the stationary signal from a wheel speed sensor (usually used for ABS and maybe traction control and similar) and that sensor is faulty causing the roof to not operate - have you consulted your handbook as to why the button flashes? A flashing button usually indicates a fault in the system somewhere so i'd suggest that as the second most likely.

***EDIT***

https://az685612.vo.msecnd.net/pdfs/..._EN_tp8337.pdf

Scroll down to Pg75 of that if you don't have an owners manual, granted it's for 2006 but Volvo don't seem to have anything older on their support site. Are you pressing the brake pedal while trying to open the roof with the engine running? That may help and also if you have any brake light bulbs out or the brake pedal switch isn't working/brake light fuse failed, it may not make any difference to the button flashing.

I was wondering if the alternator wasn't providing enough juice and other electrical items were a drain on the battery.

The only other thing I can think of is that once the engine is running, the roof module thinks the car is moving.

The MK2 is completely different to the MK1.

MK 1 only needs the hand brake applied, boot shut and in park if an auto. Although it is recommended to have the engine running whilst operating the roof mine works with or without.

Thanks for clarifying that, i'm not familiar with the C70 in any of its incarnations and suspected there may be some age related differences, hence pointing out that the handbook i found was for the 2006 model.

Either way it appears the car must be stationary for the roof to work and if it originally worked while the car was in motion as the OP seemed to suggest (although that may be me reading too much into it) then maybe there is an older fault that was bypassed and has now reappeared.

Yes, car must be stationary, hence the handbrake must be applied. The roof button light only flashes when there is a fault, or the safety precautions are not set correctly - handbrake applied etc.Very weird indeed that it all works without the engine running, but does not when it is. There is no logical reason as the car doesn't need to know if the engine is running or not.

Those were the lines i was thinking along - it suggests that one or more of the parameters (handbrake on, in P if auto etc) aren't being read or the sensors/switches are faulty so the only way it's allowing operation is with the engine off so it knows it can't move under its own power.

That is the strange thing, the engine running or not shouldn't make any difference. The op's car knows the handbrake is on so let's the roof work, but as soon as the engine is running. It decides 'I'm not having any of that and doesn't allow the roof to work.

I think I would try another roof module and see if that makes any difference.