Dead battery possibly due to Canbus??

MA3TDIQ

Registered User
Tried to get into work today and my car wouldn’t open-then opened it with the key and it wouldn’t start. My Batt is completely dead-not even a flicker of light.

I drove it on the bypass on Sunday and was sure the battery was completely charged on Sunday night. Didn’t drive it yesterday so my battery must have drained in 24 hours!

Battery is new with Lifetime warranty through kwikfit.

When I was driving car on Sunday my canbus flagged up a problem with my rear left bulb Asif it was blown. Checked the car and everything was fine! No blown bulbs at all. Did it again just before I parked up however everything was fine.

Could my battery have drained as the result of the canbus flagging up a problem with my light? If so how do I stop this from happening? I have had battery issues before with drain which I thought was coming from drain from the RNSE.

Cold weather prob wouldn’t have helped but can’t have been the only cause!
 

NHN

Retrofitter - Audi - VW - Skoda - Seat
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VCDS Map User
Pull fuse on RNS & bt if fitted, charge battery with a ctek 8 step, then see.
 

B5NUT

Well-Known Member
VCDS Map User
You say you drove it on the bypass to charge the battery, how long was this drive as from flat it would take several hours of driving to fully charge a battery.
 

NHN

Retrofitter - Audi - VW - Skoda - Seat
Site Sponsor
VCDS Map User
So if my batt doesnt drain with the RNS fuse pulled how do I rectify the problem?

I'd be surprised if it's the battery, but fault diagnosis by disabling known draining issues is a good start, then go from there.

I've replaced rns & bt units for this issue, oh also can gateways.
 

MA3TDIQ

Registered User
Why did you change your battery in the first place ?. Is your charging system good? Have you checked the voltage on the battery when the engine is running. Did Kwik Fit diagnose a battery fault?

Initially changed my batt because I got RNSE and I got constant battery drain! Then my batt died so I got it replaced. Charging system is fine.
 

MA3TDIQ

Registered User
You say you drove it on the bypass to charge the battery, how long was this drive as from flat it would take several hours of driving to fully charge a battery.

Drove it for about an hour on bypass but my batt wasn’t flat on Sunday..
 

MA3TDIQ

Registered User
I'd be surprised if it's the battery, but fault diagnosis by disabling known draining issues is a good start, then go from there.

I've replaced rns & bt units for this issue, oh also can gateways.

I doubt it’s the battery too tbh.

But how do you find a draining issue? Pulling fuses and then putting a voltmeter on the battery?
 

SpeedFerret

Registered User
Kindof. You'll need to get a multimeter and put it on Amps to measure parasitic drain. To measure amps the unit must be placed in series... ie take the
-ve lead off the battery and connect the multimeter leads between the negative lead and battery negative. There are usually two amp ranges on the multimeter so choose the range appropriate for your problem. Start at 10 amps, measure the current draw and decide whether you can move down. Read the below first !!.

Let the car 'settle' ie the amp reading will reduce as the modules on the canbus network go to sleep after you've connected the multimeter. From experience on an SLK 2006, it took around 4 mins for the network to settle for each fuse pulled. The network can take a few hours to completely settle but the current draw between 4 mins and 1 day on the Merc was a few %, so 4 mins was enough for me to be accurate

Don't be tempted to pull half the fuses out to save you some time ... known as a binary search. If you do the central gateway could get spooked and not talk to the network anymore. You're then into getting a new / 2nd hand gateway and programming it to the car.

Instead, take one fuse out of the car at a time ... wait the 4 mins or whatever an Audi takes to 'settle' and read the amp draw. If no change, put the fuse back in and move onto the next one. Make sure all doors and windows are closed. Opening a door will upset the amp reading and wake up the door control module for example.

The rule is that the last thing you did electrically to the car, is the first focus of attention when fault finding. Canbus is reliable. It's the modules or kit hanging off the network that tends to cause the problems. Good Luck.

ps Depending on how much OEM kit is on the car, anything below 50mA is fine.
 
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ab1702

Registered User
Tried to get into work today and my car wouldn’t open-then opened it with the key and it wouldn’t start. My Batt is completely dead-not even a flicker of light.

I drove it on the bypass on Sunday and was sure the battery was completely charged on Sunday night. Didn’t drive it yesterday so my battery must have drained in 24 hours!

Battery is new with Lifetime warranty through kwikfit.

When I was driving car on Sunday my canbus flagged up a problem with my rear left bulb Asif it was blown. Checked the car and everything was fine! No blown bulbs at all. Did it again just before I parked up however everything was fine.

Could my battery have drained as the result of the canbus flagging up a problem with my light? If so how do I stop this from happening? I have had battery issues before with drain which I thought was coming from drain from the RNSE.

Cold weather prob wouldn’t have helped but can’t have been the only cause!


You’ve definately got a drain somewhere so you need to find the cause of that first before anything else.
Once you’ve found it then you need a car battery charger to charge it back up to full charge and then hope that it hasn’t knackered the battery up as some car batteries don’t cope well after they have become flat.
Running your car even for a few hours will not give the battery the charge it ideally needs in the long run.
 

MA3TDIQ

Registered User
So I just jumped my car this evening have it s blast on the bypass to get a little bit of juice in it.

Turns out my canbus flagged up a bulb blown on my rear right light. Stopped and checked and this time it was actually out! Drove back home and thought right I need to change that bulb. Locked my car and with the home coming lights engaged the bulb came on again.

This got me thinking is it actually the bulb or could it just be a problem with the electric circuitry to the bulb? Could that cause parasitic drain to the battery?

How do I deal with that?
 

SpeedFerret

Registered User
Read post #10 perhaps?
 

SpeedFerret

Registered User
If you've identified the circuit, then take off the items that fed by that the circuit one by one and measure the parasitic drain.

You might want to call in a proper auto-electrician, not the twats that just read fault codes and call themselves auto-electricians.
 

MA3TDIQ

Registered User
So the plot thickens...

Jumped my car yesterday to give the battery a bit of juice and it started no problem today!

When i was driving it came up with left rear bulb error again so i got out and had a look - it had indeed gone so i thought this must be the cause of the problems.

Turns out - when I locked the car the home coming lights came on which lit up the whole light again.

Is the CH/LH circuit powered by a different circuit?

So I guess the problem is not my bulb but something else?

Anyone have any clever ideas?
 

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MA3TDIQ

Registered User
I have just done the fault finding as advised by SpeedFerret. Many thank for this advice as I managed to narrow it down now!

I managed to narrow it down to circuit 4 by pulling fuses which confirmed my suspicion of it possibly being the RNSE.

I got a parasitic drain of 5 Amps!! no wonder my battery drained overnight!

With the radio out my parasitic drain is 0.2 A - i guess this is more acceptable?

I put some VCDS on the car and got a fault code saying that my radio and canbus (strangely) has been incorrectly coded. Could the incorrect coding results in this high parasitic drain?

Or does it mean my RNSE is faulty? is there a way to connect it to a switched live only to avoid this parasitic drain?
 

SpeedFerret

Registered User
200mA is still too high (but a lot better than 5A!!). 0.2* 24hrs *21days = 100Amps. I would suggest that your battery is around the 75amp range (check on the side of the casing for the storage capacity). So, you would drain a fully charged, brand new battery between 2 and 3 weeks in theory. Liklihood is, in practice, you'd be looking at less than two weeks. But at least the car is now useable.

I'd let the car 'settle' overnight if you can and take an amp reading after 12 hrs or so. ie keep the ammeter connected overnight. If you disconnect and then reconnect in the morning you've reset the clock to zero.

Off to dinner, but you are well on your way to sorting this. I'll come back tomorrow.
 

aqibi2000

Registered User
You can modify the car to only power the RSNE when ignition is on using a relay. Easy hack which will take about 10 minutes.

Using a fuse piggy back fuse in position of the one you pulled out then wire in the relay connected to ignition (no need to mod the wires behind the RSNE).

It’s a hack but will work (could reset time etc)
 

MA3TDIQ

Registered User
You can modify the car to only power the RSNE when ignition is on using a relay. Easy hack which will take about 10 minutes.

Using a fuse piggy back fuse in position of the one you pulled out then wire in the relay connected to ignition (no need to mod the wires behind the RSNE).

It’s a hack but will work (could reset time etc)

This sounds like a good idea- where can I get parts to do this? Is there a wiring diagram to explain how the relay would connect with the RNSE?
 

ab1702

Registered User
This sounds like a good idea- where can I get parts to do this? Is there a wiring diagram to explain how the relay would connect with the RNSE?

You dont wana do that, if you do that then you’re not actually fixing your problem, think of it as more like papering over the cracks.
If you find the problem and fix it properly then you know it’s sorted and no need to mess about installing switches and fuses etc.
 

MA3TDIQ

Registered User
You dont wana do that, if you do that then you’re not actually fixing your problem, think of it as more like papering over the cracks.
If you find the problem and fix it properly then you know it’s sorted and no need to mess about installing switches and fuses etc.

I see your point however I don’t think I can get any further- I have managed to Identify that my RNSE is draining the battery as I have it out of my car now and have no issues-how do I ‘properly fix it’ now I have identified my rnse is the problem? (Apart from buying new rnse...)
 

SpeedFerret

Registered User
I'd sort if for you if I was local. I've a pretty good idea what the problem is. Seen this before and am pretty sure your interior network is not going to sleep with the ignition key out. I would reckon Ash and co can help you out if they are local.


I can run the oscilloscope over the network if their fault readers don't show anything unusual but the VCDS should show the tell tails. Again, and I feel I'm a broken WAV file on here .... last thing added to a CAN network is the likely culprit.
 
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MA3TDIQ

Registered User
I'd sort if for you if I was local. I've a pretty good idea what the problem is. Seen this before and am pretty sure your interior network is not going to sleep with the ignition key out. I would reckon Ash and co can help you out if they are local.


I can run the oscilloscope over the network if their fault readers don't show anything unusual but the VCDS should show the tell tails. Again, and I feel I'm a broken WAV file on here .... last thing added to a CAN network is the likely culprit.

Thanks for the offer! Where do you stay?

I managed to sort the issue for now-just disconnected the permanent live at back of RNSE and connect to a switched live for now... so far so good
 
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