Originally Posted by teamsmith

. Did you pull yours apart yourself? Should I invest in a cable and one of the diagnostic software packages or just take it to a transmission place and let them figure it out?

Originally Posted by KyleB

Did the valve body repair myself. I posted a thread over in the DIY section. A cable and software are well worth the investment. It pays for itself the first time you use it.

Originally Posted by BimmerFan52

I just skimmed your post quickly and might have missed something, but I would look more closely at the alternator.

I don't know how cheap your cigarette lighter voltmeter is, but you shouldn't be seeing 13V on the system with your battery at less than an 80% charge.

Failure of the voltage regulator on the alternator can be very intermittent. When mine failed, the alternator ramp up was too slow, and with an already low battery charge the ECU and CAS would throw a low system voltage fault and kick out the terminal 30g relay, which provides power to the transmission control module and dynamic stability control modules among other things, lighting up the dash. I would pull over, turn off the engine, restart and it would be fine. But as time progressed and I monitored the cigarette socket voltmeter while driving the fluctuations in voltage were getting worse.

I would suggest you probe the connections under the hood with a multimeter while someone else starts the engine cold. Monitor the alternator ramp up voltage and have the person in the car occasionally call out the voltage they see on the cigarette socket voltmeter to check its accuracy against the multimeter. The first cigarette socket voltmeter I bought was terribly inaccurate but the one I have now is very accurate compared to a digital multimeter.