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Q: What is the function of the auxiliary battery? How is it related to the intelligence servo module?

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I replaced the ISM ONLY about six months ago and now it is bad. What could be the problem?

My car has 110000 miles.
My car has an automatic transmission.

Hello - these two components are unrelated. The principle function of the secondary battery is as a backup for the primary battery - for the Sensotronic Brake System, which uses electronic pumps for brake pressure to each wheel - not hydraulic fluid pressure from a master cylinder powered by the drivers foot. The Intelligent Sensor Module is an interface on the automatic transmission that translates "gearshift selection" requests from the driver (which are electronic in this vehicle) and translates them to physical gear selection in the transmission.

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