SC430 specialist North London

[Clueless1]

MY 2006 SC430 has a Battery drain issue so I'm looking for an SC430 specialist within a reasonable distance of Ware in Hertfordshire.

The car won't turn over if it's left for more than a few days; I've had it checked by a vehicle electrics place and they couldn't find anything.

[cruisermark]

Have you check the boot lid light (if it has one is going off when closed?

Also if you have a factory phone installed - they don't normally switch off with the ignition.

Japex in Kings Langley (although not electrics specialist) are highly recommended for all things Lexus

[mw430]

My 2005 SC has always suffered from battery drain but it's taken me a decade to get down and test where the current's going.

Initially I bought a new Toyota Battery. In those days the car was used a few days a week and the Battery failed to start the car about every 2 weeks. So for years I charged it, and all through lockdown I used an intelligent charger. The car was never used except to go to the garage for its MOT.

Now the Battery is flat after 3 or 4 days and, having tested it I am no closer to solving what causes the problem. 

Remote locked or unlocked the drain starts at 850 mA, quickly drops to 125 mA and then settles down to 40 mA, enough for a 1/2 Watt LED.

No wonder no-one's come up with a definitive solution!

[mw430]

...and despite this minimal current drain the Battery went flat in 5 days!

So, it looks like the intelligent charger must be connected all the time.

Unbelievable for such an expensive car.

[Bob King]

These cars been over 50k when new sometimes had a tracker fitted when new. Even if the subscription expires the tracker keeps sending out its signal.

           As they are fitted as a security item you won’t know were it is on the car .....this is going to cost you time but removing all the trim panels in the boot is a good place to start looking.

     Look for none standard wiring around fuse boxes in boot, interior kick panels and engine bay 👍🏻
Member on the Lexus World forum had two trackers fitted, he found them both in the boot..each side.

The alarm has a Battery back up inside and the Battery can corrode with age...so also with checking out 👍🏻

[mw430]

I carried on testing the Battery and came p with something that was a complete surprise.

Each day I checked the voltage and it measured, each day from the day after charging, 13.1, 12.95, 12.89, 12.68 and then 10.4 V!

In case I'd done something to make this happen I repeated the tests. They were, 13.13, 12.95, 12.85, 12.77 and then 10.7 V.

Can anyone help me understand what's happening, please?

[ColinBarber]

Three things normally get the blame for excessive power draw on the SC430.

• The amp for the sound system (pull the radio fuse or disconnect the amp)
• Auto headlights (turn them off, don't leave in auto position)
• Alarm backup Battery

Not sure what would be triggered after 5 days to cause the excessive discharge. The only thing I can think of is the alarm backup Battery becoming discharged and causing some malfunction that draws too much power from the main Battery. The other two causes I'd expect to produce excessive draw immediately (or in the cause of the auto lights at most once you go through a light/dark cycle (e.g. overnight)).

[mw430]

I can't believe that after 5 days something switches on and drains the Battery, but with this car I shouldn't discount anything. I just can't think of what I can do to detect when, and if, the "normal" drain of 50mA suddenly ramps up, if it does!

Where is the alarm Battery and what type is it? If I disconnect the Battery when it's charged the alarm sounds so, at that point, its Battery may well be charged too.

I have a smaller spare Battery that's in perfect condition, taken off a car that needed more oomph. It's kept its 12.7 volts for many months. Changing the Toyota one for that one it'd be interesting to see what happens over a week or so starting from fully charged. The Toyota one's only done 6000 miles and II accept it could have aged with lack of use but I'm baffled as to what can happen inside the Battery at a roughly specific time to drop the voltage by effectively one cell!

An inability to retain charge was the reason I bought a new Battery in the first place, but I never tested the drain so the Battery might have been in poor condition. However the new one only took a few months to behave like the old one. With all the reports of this not being unexpected in an SC430 I saved myself the hassle and didn't make a claim...I just lived with it. Now I'm intrigued.

 

[mw430]

Now I have tested the 2 batteries for 6 days I'm no closer to finding out anything useful.

The disconnected Toyota Battery measured 13.81/13.31/13.3/13.27/13.25/13.23 V over the 6 days and the old, connected, Cavalier Battery measured 12.69/12.5/12.47/12.41/12.37/12.33 V. Neither set of results is surprising and nothing, to my mind, indicates either Battery is defective, or is this a wrong assumption?

Next I'll rig up a 5mW load while the Toyota Battery is still disconnected and check again...a 220 ohm or thereabouts resistor should do.

[ColinBarber]

3 hours ago, mw430 said:

Next I'll rig up a 5mW load while the Toyota battery is still disconnected and check again...a 220 ohm or thereabouts resistor should do.

I assume you meant 50 mW? 220 ohm / 1 W resistor will do the job.

The Toyota Battery is currently behaving like a capacity, with some charge on the plates - you need to put some load on it to make it drop down to a normal 12.7 v.

[mw430]

Yes. I did mean 50 mW. Thanks.

I had started the engine twice before I started the last tests to try to shock off any coatings the plates might have...and after that the voltage was above 13V. It had been over 14 V before that.

I'll use a tyre compressor as a load as you suggest. It takes 10 A and we'll see what the result is.

Then I'll check it with a 50 mA drain.

[mw430]

Yesterday the Cavalier Battery read 12.4V. Today it read 7.7V.

It's been connected as the Toyota Battery replacement for 3 weeks and nothing on the car's been touched. It was left unlocked with no alarm and no doors have been opened.

The Toyota Battery did much the same thing in a third of the time, so maybe it is the car doing it.

I haven't done a controlled drainage test yet as what's happened makes that seem irrelevant.

I really don't see the next step except to buy another Battery and see how that behaves.

[mw430]

I guess the final thing, which I found really surprising, was that when I began to charge the Battery from its 7.7V state, its charging current went to what I'd expect from a near fully charged state in just over an hour.

This reminded me that that's very similar to what happened when I started charging the Toyota Battery after it droped to 10.7 V.

I can't work out why that should happen so I must admit to not understanding car batteries.

My investigation's over and I'll have to rely on a new Battery.

[Bob King]

Did you check for a tracker in the boot as I suggested earlier in this thread ?