2002 V40 Stalling Issue (Electrical)

[techneighbor]

I have a 2002 Volvo V40 that has been having a stalling issue for a while now. The problem is it rarely happens so it has been hard to diagnose. When it does stall it will be while the car is stopped, like at a stop light and when it stalls it is like someone turned off the key, no rough idle, it just goes off. Normally it will start right up.

I have always thought it was an issue with the electrical system and I have been driving around with a volt meter that plugs into the cigarette lighter and it constantly is reading the voltage. After starting the voltage will read around 13.4 volts but after driving around the voltage will drop below 13 volts. The other day it stalled again at a light but this time I was able to gather some information since the car would not start right up again.

This is what happened. Car stalls, ignition is still on but all the indicator lights on the dash are off. I turn the key to off and then turn it back on. I look at the voltmeter and it is reading around 6 volts. Try to start, but just click, click, click, voltage too low to turn over the starter. Turn the ignition off again and then back on. Voltage is around 10-11 volts, turn to start and the car starts. This all happens in less than a minute.

Wife uses the car a few days later and she says it stalled twice and the radio loses the anti-theft code. This also seems to indicate a low voltage situation. But in her case the car started again right away.

Battery was replaced about a year ago because I thought the original battery might be a fault. It was not. Terminals are clean and tight. Battery voltage with the car off is about 12.7 volts. Another interesting fact is that if you charge the battery the problem does not happen. I charged the battery and my wife used the car with no issues.

My current theory is the alternator\voltage regulator is faulty. That under certain circumstances there is a short duration short circuit that causes the voltage to drop so low that the cars stalls. Once the voltage recovers that car starts up and runs fine. I don't think there is a device (fan, lights) that have a fault because most of those are protected by a fuse and no fuses are blown.

So if anyone has any ideas or suggestion I would appreciate your input. Also if I do change the alternator can you recommend a place to purchase one. I know Volvos can be finicky about replacement parts.

Thanks

[S40Mark]

The voltage dropping may indicate a bad voltage regulator, or just that you had more appliances drawing current and the alternator wasn't putting out enough to offset the extra draw.

Since the engine stops and the dash lights go out "like someone turned off the key" I'm suspicious of the ignition switch. Possibly a bad connection or ground, but you said it yourself..."like someone turned off the key".

I'm new to Volvo's but I've had faulty ignition switches on other cars and it seems like a good place to start. Maybe someone else has an idea of how to diagnose / rule out the switch on these cars?