Power TCU trough Ignition position -Battery Drain- Solved
 

Well, it seems that the day has come for our 2005 x5 3.0i to start draining the battery because of a somehow faulty TCU unit. The bluetooth module (Fuse 74) seems to keep waking up the car from sleep mode every 10/15 minutes or so, drawing a 0.5Ampere for a few minutes. Result = dead battery after a night or two in cold days.

Long story short: Besides this power drain, the bluetooth module is working great and I love the quality of the microphone and everything else. I really would like to keep it in working condition.

The solution that came to my mind is to power the TCU trough a power source that is directly bond to the ignition switch position. Logic: Key turned = TCU powered, Key removed = TCU without power.

I could cut the original power supply to fuse 74 and steal the power from the rear lights, but I guess the LCM would notice a too high power drain. Maybe some of you have a smarter idea or approach on how to power this unit (obviously always securing the circuit with the proper fuse).

The usual fix is to simply pull the fuse for a day or so then plug it back in. For whatever reason that seems to usually remedy the problem.

Maybe approach the problem at a different angle. Use the same power feed but install a relay to open the existing circuit when the key is off. Not sure though what effect this would have on the TCU operation, it might need to have power all the time or maybe need power before the key is turned on.

I can not imagine that it will cure the problem permanently, or have you experienced it? I took the battery out of the car to recharege it - this should be equal to pull the fuse, and only after reattaching the battery I looked for the drain and found it. That tells me that the problem is always there or, at least, coming back when it wants.
I will now use the car without fuse 74 in the coming days, to confirm the culprit 100%.

This seems to be a nice strategy in fact - the relay would be piloted by the rear light supply, right?

Prior i will obviously check if the system works when the tcu is powered on later...

There must be other circuits you could use, but yes if you want to use rear lights then using a small relay (and a capacitor and diode because the light circuits are PWM) you might be able to get away with not triggering a warning from the LCM. Does the power draw come from the TCU itself or the fact that it wakes up the car?

Fuse 74 responsible for:

• Telematics Control Unit (TCU) or Universal Electronic Charging & hands-free unit (ULF)
• Voice Input
• Eject Box
• Compensator

I cured mine by removing it and putting it in a box in the house. Hasn't bothered anything since :)



I tried replacing it at first with a unit off ebay which worked for a week or so and it was back draining the battery again.

Went to an aftermarket radio and ditched the tcu was the final solution. That said your idea of making it key switch would be a good solution.

I have experienced it. Both times after an alternator failure. Disconnected the TCU and reconnected later. Problem solved. If it doesn't, pulling fuse 74 will confirm it is actually the TCU. If you pull the fuse and leave it a couple days and the battery isn't drained, there you go. If it doesn't, then it's something else. Other culprit is the NAV if you have it or the FSU.

Thanks a lot to all for the help.


I actually don't think the faulty part is the TCU (even if it's the one which drains the power). The fact that you replaced yours and had the same problem a few days later somehow confirms this thinking.
In my case the module keeps waking up every 5-10 minutes ...draining for 3-4 minutes and then goes to sleep again. I really would like to understand what is causing this but....it's so time consuming that I really tend towards simply cutting the power supply trough the ignition switch position.

Just wanted to give a final update. Powered the TCU trough a relay related to ignition switch position. Car can now be left parked for over 10 days and fires up like a dream. The Bluetooth module / function still work like they always did, great!!



If anyone should ever need a guid on how to manage this issue, I would take a picture and explain what's needed.

A guide and picture would be great! :excited:

There you go...at least a picture of the work. The relay is on the left with green/yellow/white wires. Basically I set it up the way that the new relay is powered by the relay of the rear defroster, which gets power only when you turn the key. If i remember right, the white color wire of the relay is supposed to be connected to "-" and the yellow one is "+" which i got from the rear defroster underneeth the green relay.

Once activated the relay closes the connection between the green wires which I connected with the stock fuse source (red cable) and powers the TCU unit. Obviously i installed a 10A fuse on the red cable....


It's not the cleanest of solutions but it's 100% reversible in any moment - that was my priority.

That is freakin awesome, great engineering and I’m sure something that will be put to use many more times as our X’s continue to age ☹️


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Thanks for the kudos! I'm planning to keep this car for at least another 10 years so... I will have to stick other "patches" here and there for sure:D

You should add the terms "battery drain" and "solved" to the thread title just for people searching. This is a great solution to a fairly common problem. Nice work.

I heard that, that's why I did my own VSS job! - I've had mine for a bit longer than 6 years now and planned on keeping it "forever"... but I've fallen in love with a blue 2012 X5M... that my wife DOESN'T want me to have.


After all the "fun" I have had with my current E53, she has no idea why I would ever consider owning another one :rolleyes::rolleyes: LOL... I tell her it's because the things are so damn hard to hate! I know the enjoyment my current X has brought me, I can only imagine the enjoyment that 550 HP of TT power would bring me :rofl: That's when she quickly reminds me of the whole new set of problems that I would be taking on... which is why I haven't bought one yet... hhhhhuuuu

I see your point:D Actually I would be probably thinking about a upgrade too, if money was all around me. That's not the case and actually the whole family loves the car and I enjoy repairing it so... looking forward to another 150.000miles :-)

Pulled out the TCU on my 2006 x5 e53 and it seems to have solved the flashing screen on my head unit and the battery drain so far *fingers crossed*

So turns out the flickering is back after really wet humid weather even without the TCU, haven’t been able to check the power drain as have been driving it everyday... no idea!

What are these items?

Eject Box
Compensator

I think the eject box was for handheld phone technology that existed in the early 2000's. I think it was wired for provision under the armrest. The compensator I have no idea but probably phone/TCU related.

The TCU is the unit for bluetooth for phone. It is notorious for creating parasitic drain.

Thanks.

Yanked the TCU after charging up my dead battery..... let's see if this works...

You could have just pulled fuse 74 but removing the TCU achieves the same result identifying the TCU as the issue.