Windows
 

C70 windows dropping when ignition turned on

Often a symptom of low charge in a nearly flat battery in a number of Volvo models.
However, if yours in a cabriolet ie soft top C70 there might well be a fault in the window control module or a faulty window position sensor. If all four windows drop around 2 to 3cm - it is most likely a fault in the windows control module unless the roof hasn't completely seated when it was last raised.

C 70 windows
 

Hi, thanks for the reply, this fault does not seem to affect the soft top which works ok. All windows drop when moving through ignition when starting or switching off. If switching is down very quickly it does not happen. It seems that a live connection is made at second contact on key in switch. When engine is running or off, the windows can be returned to closed

A cold reset will often clear module problems.
With the hood fully up and locked, turn the ignition off, wait ten minutes for all the modules to power down, then disconnect the battery.
After a couple of more minutes, cross connect the +ve and -ve leads to clear all memory in the system, then with the light switch set to daylight running lamps or dipped beam and the key in position II, which prevents a voltage surge/spike firing the air bags, reconnect the leads to the battery.

If the windows still drop when turning the ignition on, then the most likely cause is a module problem; to find out exactly what is going on, you need to get the codes read using a Dice and Vida, a basic OBD II code reader will not read Volvo hood/roof codes.

NB Volvo dealers often outsource hood problems after reading the codes!

As an engineer that technique sounds truly terrifying, to reverse polarity of the battery....

I must say I would not do that myself, I would be terrified of damaging something (at the very least fuses).

Taking the battery off yes, but cross connecting it, I wouldn’t myself.

Windows
 

I think what he means is to "touch the +ve and -ve cable terminals together", not "touch the cables to the battery the opposite way around".

At least, I hope so.

Yes, connect or touch together the red covered positive lead connector to the back negative lead connector or any bare metal part of the car's frame for a second or two DEFINITELY NOT WHEN EITHER ONE IS CONNECTED TO THE BATTERY

Windows
 

Hi George,
It might be a case of cleaning the connections that bring the electrics from body into the doors. Positioned close to the door stay, N/S & O/S, unplug and clean the plug and socket connections.
Fred

Fault found, water damage in roof control unit