jb.1981

Factory headunit parasitic drain?

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Hello all, new user here.

I have a Battery drain on an '03 IS200.  I have run a parasitic test and concluded that the headunit was drawing a lot even with the key out of the ignition.  Couple this with the fact that I can switch the stereo on without the key and that it doesn't turn off automatically when removing the key, I clearly know I have a problem.

 

The clock on the dash also remains backlit at all times.

 

I have removed the fuse for the headunit and I can now start the car everytime, providing I drive it at least every 3-4 days.  I recently left it for about 10 days and the Battery was flat as a pancake again (clock light maybe)?

Is this a common issue?  I understand this could have happened with a poorly installed aftermarket stereo but this is factory and the wiring and harness look original.

 

I'd like to get music again so I'm tempted to get another factory unit from the breakers yard but the clock light in particular makes me think I still haven't found the root cause.

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Does it have a sat nav?and no its not a common problem,only when the wiring has been fiddled with,  obviously someone has messed about with yours at some point 

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It's not a problem I've come across before and sounds like someone has arsed about with maybe an aftermarket unit and then put the original back in. Something along those lines. I think the problem with the clock is the clue that something has been rewired incorrectly. I don't think one from a breakers would solve your problem.  Also, does the 200 have an in dash changer? The CD changers are a real weak point on the IS and there's a real risk that you'd be buying a duff one.

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Yep, the head unit is only a symptom, not the cause.

You need to do some proper diagnostic fault-finding with the correct tools for the job, such as a multimeter and a clamp ammeter to name just a couple.

There's no shortcut to this, which is why 'auto electrician' is a separate trade to motor mechanic.

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We've got the same problem with our 2008 IS250. 

The Battery and alternator are fine, so we had an electric specialist come and have a look. We learned that there's a parasitic drain from the onboard body control module which is discharging the vehicle when it's switched off. The body control module also powers the audio module which is another item that can sometimes have this parasitic drain problem. 

Either way it needs repairing or replacing and 'regular' garages don't seem to have the software or coding skills needed to fix it. So it will have to go to Lexus & that's going to cost a lot! 😞

Has anyone managed to remedy the problem? If so, how and how much did it cost?

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There is always going to be a parasitic drain because things like GPS, radio presets, clock and other stuff need to keep their settings.

The question is, how much?

Around 36mA is considered to be normal, some cars even going up towards 50mA, but anything above that and there's a fault somewhere that needs to be found.

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The series I IS had some water ingress issues which causes electrical problems, although normally with the headlights. Worth checking the interior fuse boxes and junction boxes for water/corrosion.

 

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Hi. 

The discharge rate was 0.4 amps. I don;t really know what that means but we had the car about 4 years and it wasn't an issue before. 

The drain was so 'strong' that a new Battery was reduced to 43% of its life within 2 months. 

Not using the car for a day or more resulted in the Battery being so flat that we couldn't even lock the car with the button on the key, but had to do so manually. 

We have now sold the car. We got less for it because we declared the fault but that's only fair. 🙂

 

 

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11 minutes ago, HeenaM said:

The discharge rate was 0.4 amps. I don;t really know what that means but we had the car about 4 years and it wasn't an issue before

So that's 400mA which is way above normal.

It's a shame that we'll never know what the fault was but I'm glad it's no longer a headache for you.

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Thanks for explaining.

I agree. 

I would have liked to know but I already paid £130 to find out there's a parasitic drain from the onboard body control module and that the body control module also powers the audio module which is another item that can sometimes have this parasitic drain problem. 

I would have had to pay nearly £200 for Lexus to investigate it further or take it out of London for a (non-Lexus) specialist to check it out and THEN pay to fix it. 

You're right. It was a headache and I'm so glad it's over and done with. 🙂

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I had a similar problem with my son's Grand Voyager. To keep costs down I put a relay in between the Battery and the devices giving the excess Battery drain. The relay was operated by turning on the ignition switch powering up the devices. This cured all his Battery discharge problems, and is still working 3 years later.

John.

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Wow! 

That sounds amazing. 

I'm glad it worked and continued to work for so long. 🙂

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