Disconnecting Battery

[johnjp]

A naive question perhaps! What will happen if I disconnect the battery?

[neil stevenson]

Car won't start, radio will lose its code, nothing electrical will work.

[johnjp]

what I meant was what will happen to all the SENSORS when I disconnect to charge the battery and reconnect! I`m not so daft!

[Andy_Gibson]

well besides the obvious of the radio code, nothing else will have faults.
the car will start up just fine so dont worry about swapping batteries

[ivor940]

Hi, On Ford Mondeos, if the battery was disconnected without a "Code Saver" being plugged into the cigarette lighter, the ECU lost it's settings and the radio needed the code . If you did not have a code saver ( or other method of keeping voltage in electric system ), you were to run car at less than 2000 rpm for a period of min ( 5-10 min I think ) and then drive on varied roads for 15-30 min. This enabled the ECU to "relearn " its operating parameters. Does this apply to Volvo ECUs?

ivor940
94 940 2.0 SE Turbo Estate 5 spd 165k
VOC member

[ascott1]

Hi Ivor,

The "relearning" activity probably depends on the Volvo ECU (there's lots). On my former V70 10-valve \<spit\> the fuel trim values seemed to be learned over 200-300 miles; so if you got a fault code on fuel trim and cleared it without fixing the fault, it sometimes came back after that distance. That model had an unusual Siemens Fenix ECU, most seem to be Bosch.

On my Mondeo 1.8LX 16-valve, if you disconnect the battery, sure enough it runs a little lumpy for a while as it relearns some settings. But I read about the relearning procedure you describe, in a Haynes manual and tried it; it doesn't seem to make much difference. If I have time to drive around like that after reconnecting the battery I do; otherwise it learns anyway.

More useful for both the 1.8LX and other multi-valve Volvos (not so much the 10-valve V70) is the monthly "Italian tune-up" to rattle the valve lifters etc; or maybe it just cleans the plugs a bit. Anyway, I do feel a difference after doing that on my Mondeo and 960 24-valve, even if it's only subjective. I'd rather spend 5 minutes doing that than 20-30 re-educating the ECU.

Originally Posted by ivor940

Hi, On Ford Mondeos, if the battery was disconnected without a "Code Saver" being plugged into the cigarette lighter, the ECU lost it's settings and the radio needed the code . If you did not have a code saver ( or other method of keeping voltage in electric system ), you were to run car at less than 2000 rpm for a period of min ( 5-10 min I think ) and then drive on varied roads for 15-30 min. This enabled the ECU to "relearn " its operating parameters. Does this apply to Volvo ECUs?

[johnjp]

An `Italian Tune-up`?

[Citizen.Agfa]

Originally Posted by johnjp

An `Italian Tune-up`?

Take the car for a run on your favourite route and rev the bejasus out of it! It sounds cruel but it's amazing the difference it can make.

Good luck, Nick.