BOBBY BIRD

jump started battery wrong way round

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Hi,  My battery was flat and so I connected jump leads from a good battery BUT the wrong way round!!!  Changed it round to the right way and car started BUT only in limp mode (no acceleration) couldn't drive and no dash lights etc. I replaced the 140amp alternator fuse and three other fuses and it now starts and drives. However the VCS light and engine light  and warning triangle is on and dash read out says check VSC.

Could this be a real fault or just a warning light that needs cancelling somehow?

Any advice welcome.

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A well engineered electronics system will put a Hi wattage diode in series with the battery so that if you reverse the battery, the diode will appear as an open circuit, essentially.  But w/o an electronic diagram, there is no way of knowing. I’d get it on the computer and see if that poor thing is still alive.  Possible that some devices are protected up stream from the battery, like the computer, but others are not diode protected. 

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I've been using an old 10 A battery charger periodically (couple of hours), when not using the car much. In general, a lead/acid battery is essentially a constant voltage source and it doesn't care much what connects to it in terms of voltage passed on. While I thought that would block any AC component from the battery charger, perhaps not enough on the Lexus.  After the last time I used the charger (done many times before), I now have the VSC indication described above. I pass this on as a caution, I'm getting a new battery charger after I fix the problem. By the way, Lexus starts to describe the diagnostic tests on page 5-483 in the repair manual and VSC trouble codes are on page 5-499. No indication of an ABS issue, so I think the problem is in the only with the VSC sensors and I'll update this post after I fix the problem.

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Your battery charger produce either true 14.7 volt DC but most likely it is pulsating DC which is not considered to be an AC component.  Your battery loves DC and PDC for charging purposes.  The car eletronics is designed to take pulsating DC and filter it out with a filter capacitor (called and RC network) so that the electronics sees only pure DC Direct current. I have an old charger that is nothing more than a transformer voltage reducer and a bridge rectifier which produces unfiltered pulsating DC current.  It will not harm your electronic system.  Lexus, I’m sure, takes great pride in being able to pass only DC coming from any make of charger, so long as it is not devective. But you do want to make sure your charger has an overvoltage (crowbar) that will trip off the charger on an overvoltage conditon resulting from a malfunction in the charger.

Waiting to hear how the VSC trouble could be connected to charging the battery. But you are right to get a new one just to be safe, no doubt at all.

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Hi,

I agree with everything you said and possibly my new VSC warning has nothing to do the with battery charger. My old charger is the simple step down transformer and a rectifier, producing the pulsating DC that you reference and dropping charge as the battery voltage increases (10 A max in any case). My old scope stopped working, but that is what I can see with a simple meter measuring the pulsing as an AC component. More to come later as I find out if my Auto Enginuity scan tool can pick up the non-emissions codes, not much hurry as I did verify that ABS is still working which mostly leaves the yaw and steering angle sensors to be checked.

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Great, Bob!  Sounds like you are on you way to figuring that one out.  What you see on the scope, as you know, is measured as “Ripple” by the electronic designers and they have to be able to filter that out per the specs they are required to meet. 

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