Cal Switch Issues

[RichardB]

Hi Pat,

Yes we are talking about the same spiral wound gel batteries
If I look at a vbat trace in my recent logs, it seems to start around 14.4 volts and drops to slowly to around 13.8 volts over about 10 minutes which seems a little odd. Alternator state is also showing as OFF for the duration.
I had a look last night and I am only getting 150 to 165rpm when cranking, so something is not happy.
I also noticed that the connector on the negative post was a bit loose ... it is as tight as it will go but still not making brilliant contact (i.e. it still turns a bit on the post). I am going to replace this first with something better fitting and if that doesn't work ... based on your previous post I guess the starter motor would be candidate number 2.

Thanks
Richard

[pat]

Richard,

The voltage profile you have observed is "normal", it should start at 14.x and drop down, so that sounds like it's right. The alternator state is used to track the alternator control strategy on the ECU, but you should find that the Alternator Control output function has not been assigned to any output, ergo it won't be doing anything, the alternator will just charge anyway.

The cranking RPM does indeed seem a little low. It is curious that the problem only materialised after a while, and that you didn't have it previously. An Optima gel battery is a really good piece of kit and I'de be shocked if it wasn't able to spin the engine any quicker especially since it's obviously getting charged. You could take a look at vbat during cranking, that might identify any potential wiring problems; the voltage shouldn't really fall below 11V on an Optima, if it does then bad connections / cables are likely culprits.

If the voltage stays good but it still won't turn over any faster then you may indeed be due a starter motor. They are normally pretty good on Subarus but nothing lasts forever!

Good luck with your quest to find the cause.

Cheers,

Pat.