Parasitic Drain

[Mark Peyton-Welch]

Im sure this is not a new problem. My S4C430 Battery is running flat after a few days non use.  Ive had it checked and the Battery is fine. Ive checked the boot light and that does go off when the boot is closed.  

My friendly Lexus dealer was not really interested and could not give an estimate for correction.  Apparently the fault could be anywhere within the electrical system and could take forever to track down. Could anyone confirm if this is really the case, or give any pointers on where the fault may be.

Thanks

Mark

[steve2006]

Hi Mark and welcome to the LOC,

First thought would be the Battery...how was it checked?

You need a multimeter to measure the current or better still a clamp meter which saves disconnecting the Battery. With the car in full shutdown i.e. engine off and car locked the drain should be no more than 80-100mA.

Anymore than that and it’s then a case of pulling fuses and rechecking, when the current falls that is the fuse powering the circuits and causing the drain on the Battery.

[ColinBarber]

What seems to be a common issue is the stereo amp on the SC430 as a source of excessive drain. Several posts about this over the years. Worth starting with that fuse.

[Herbie]

2 minutes ago, steve2006 said:

Anymore than that and it’s then a case of pulling fuses and rechecking, when the current falls that is the fuse powering the circuits and causing the drain on the battery.

With the greatest of respect Steve, that's how it used to be done but it's not recommended now with modern electronics because pulling the fuse could reset the very thing that you're trying to find. I would also say that 80-100mA is a bit high. I would say about 35-50mA is more 'normal' although it obviously does depend on how many things need to be kept alive, so as manufacturers add equipment maybe I'm a bit behind the times and you're closer to the mark. The actual figure can sometimes be found in the specs for the car.

Anyway, this video shows the preferred method of faulting a parasitic drain on modern cars:

 

 

[ColinBarber]

2 hours ago, Herbie said:

Anyway, this video shows the preferred method of faulting a parasitic drain on modern cars:

Provided you have fuses with live parts exposed. The fuses on the right clearly don't.

[Herbie]

4 hours ago, ColinBarber said:

Provided you have fuses with live parts exposed. The fuses on the right clearly don't.

That's true, but I think they're old ones. I don't think you can buy them now without live parts exposed.

It's also true that just pulling fuses can reset whatever is causing the problem which means you won't ever find it. Given that the fuses aren't all that expensive, I think I'd be replacing the ones that don't have live parts exposed with ones that do, if the first round of testing proves inconclusive.

[Neil E]

Very good advice. I did this the other day whilst checking the sat-nav and all of the mini fuses in the SC430 (it's a 2006) were possible to test without removing them.

I agree with Colin, if it's draining quickly say within 24 hours then investigate a possible amp draw but it is common for an SC430 to drain even a good Battery in 3-4 weeks. Some owners use a Battery tender.

[oldjoe]

i remember reading on one of the forums of a back up Battery to do with the alarm system buried behind nearside rear seat that corrodes over time and creates this leakage as the main Battery is trying to keep it charged