S60 Erratic Wiper Function

jev · Post by **jev** » 21 Apr 2019, 04:41

I all, I could use some help. 2004 S60 w/rain sensor feature. For quite some time the wipers were not really following the wiper switch positions. I had tried changing the wiper switch but no change. Hindsight tells me that there was something wrong with the rain sensor which until the latest problem I didn't even know the car had. The latest problem is that suddenly one day the wipers now run by themselves meaning that with the switch in the off position they will run for a few seconds then stop then run then stop etc. When they stop they do not "park" they just stop. They now do not follow the wiper switch at all. I have checked grounds and many connections. The car is in very good condition and all grounds and connections are corrosion free. By accident this is what I observed. Disconnect the battery and wait. Reconnect the battery and turn the key to ON and everything works normally. Start the car and everything goes nuts again. I have the rain sensor unplugged but all things remain the same whether plugged in or not. Go through the battery ritual again and remove the belt from the alternator or remove the power cable from the alternator and everything works normally. I have changed the alternator hoping that the regulator was at issue but no luck. When the car runs it maintains about 14.3v. I also tried connecting the electrical system to another running vehicle with the belt removed from the alternator. I could only get the voltage up to 13.8v but everything worked normally. Seems odd that an extra .5 volts would change things. The UEM is probably my next target. Any other thoughts? I don't really want to just start throwing parts at it until I find it. I have tried a different known good rain sensor with no change so I just leave it unplugged.

Post by **chrism** » 21 Apr 2019, 07:31

What happens if you just have the key in Position 1 (engine not running)?

jev · Post by **jev** » 21 Apr 2019, 09:21

I had to go check just to be sure. I don't believe that I ever tried it in position 1. I always went right to position 2. With key in position 1, what I would call the accessory position, (engine not running) the wipers are normal. All is normal until I start the engine unless I remove the belt or power cable from the alternator.

Post by **chrism** » 21 Apr 2019, 11:48

I had a drivers window control switch (DDM) that misbehaved in somewhat the same manner - OK with the key at position 1 but acted up with the engine running. A replacement switch was the ticket.

You say you tried replacing the switch? Are you confident you installed a good one?

jev · Post by **jev** » 21 Apr 2019, 12:02

That is very interesting. Yes, I have tried 2 "known good" switches. They both acted the same as the original. After reading your experience I am going to get a new Volvo switch. It is probably the least expensive thing for me to try at this point anyway. I find it totally bizarre that everything is normal until the alternator gets involved. Thanks for sharing your experience.

Post by **chrism** » 21 Apr 2019, 13:30

Also I’m wondering if there is some sort of electronic module at the wiper motor end of the system that could be the culprit.

jev · Post by **jev** » 21 Apr 2019, 18:42

The wiper motor/transmission itself is very simplistic. No electronics in the motor/transmission assembly. There is a simple "park" switch that is connected directly to the CEM. The switch seems to work 100% of the time.

Post by **abscate** » 22 Apr 2019, 04:41

Voltage fluctuations will wreak havoc in P2 Volvos. Get that sorted first. Good battery and well performing alternator. I suspect you have bad diodes and ripple current on the alternator.

jev · Post by **jev** » 22 Apr 2019, 08:09

Thanks abscate! Bad diodes is exactly what I suspected in the first place. I did try a "known good" used alternator because it was quickly available. It made no difference and I was extremely bummed. Not necessarily a conclusive test of course. Because your input supports my original theory I am going to get a new alternator. The battery is less than 4 years old and still seems OK but it can't have much time left anyway so I might as well replace that also. At least now I don't feel like I am just throwing parts at this car to try to fix it. Thanks again!

Post by **jimmy57** » 22 Apr 2019, 08:58

Engine running is a different status on the network. The SWM(steering wheel module), the plate the stalk switches mount to, could be going offline and then the wipers will default on for some P2s. Have you noticed if turn signals function or high and low beams can be selected when wipers are doing the weird things?