We have a 99 S70, the belt tensioner broke and my wife had to keep driving until the battery gave up. She got the new parts put on the next morning, and then had the issue with the trans going into the safe mode. Se made the 150 mile trip home, OK. Now I discover the tachometer is not working, and the trans problem. I didn't have the flashing arrow, but a solid arrow and wont downshift to low, and a small miss in the engine. The auto parts code reader came up with O2 sensor and Idle air control reading a little high. My guess is the low voltage may have damaged some solinoid, fuses or curcuits. Are their any test that I can run to troubleshoot this at home?