OBC/Taco/SI Batteries

Post Thu Mar 12, 2020 1:21 pm

Read a lot about this some saying batteries have no effect on OBC.Anyway my problem was a fluctuating taco,, it would bounce (slowly) 2 or 3 hundred revs as you drive along. So at say 2k revs it would bounce between 1800/2100. OBC gave weird mpg/temperature and eventually no readings at all, just an illuminated but blank screen. Removed the SI board and battery’s read .4 and .6v. These batteries are probably 12/15 years old. I have replaced the batteries and all the problems have gone away. If this helps anyone then great.

Post Thu Mar 12, 2020 2:25 pm

OBC gets all its signals, except outside temp. from the instrument cluster. All the electronics for everything in the cluster, except the speedo (electronics on own daughter board), is on the SI board, and can all be affected by duff batteries pulling down the supply to the electronics, so it's reasonable to assume that the OBC can be affected.
Were your batteries NiCd or Lithium - manganese?

Post Thu Mar 12, 2020 4:12 pm

Lithium 3v each. Thanks for the post. Because of what I’d read I pissed about looking for loose wires and such. In hindsight I should just have come on here and asked

Post Thu Mar 12, 2020 6:34 pm

Shelf life of a Lithium Manganese Dioxide battery is between 10 and 20 years, depending on temperature. Service life should be close to shelf life in the E30 application in the case of a car that is in daily use, since no current is drawn from these batteries when the main car battery is connected, but as more and more E30s become garage queens or only used in summer, and spend time with their main battery disconnected, duff SI batteries are going to become more common.

Post Sat Mar 14, 2020 8:24 pm

Put OBC back in along with an older stile Becker radio which seems more in keeping with the time period. Buggered if I can figure out the satnav.

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