WEAK BATTERY Warning
 

I had stopped for gas and turned off my car. While waiting, I notice the screen says 'Weak Battery' then something about 3 minutes until it shuts down.

I have 39k on the car. My Audi care just ran out (of course) and I haven't done my maintenance yet only because I am not paying $500+ to Audi, so I need to schedule with my mechanic.

Do I need to replace it or just run a diagnostic on it to see if there is another issue? Winter is here, so I don't want to get stuck with a dead battery, but I wouldn't think it would be due for replacement yet.

Thanks

Do you have the VCDS tool? Is this the original battery, Trlyka?

I have a Vag-Com, but unfortunately the laptop I use for it won't hold a charge, so I need to see if I need a battery for it. Yes, it is the original battery.

If it's the original battery, 5 years is about right for its life. Audi Care wouldn't have covered a replacement battery in any case.

Ok, fair enough. Just as I am saving some money for the holidays....ugh

Hey there, just wanted to know if it was the battery in the end? Or if not, what else it could have been? I have just had my battery replaced as I also was experiencing random Battery Weak messages whilst driving. Audi said it was the battery as there was an aftermarket one in there, they changed it, after a week the messages started popping up again. Twice I had to pull over, turn off the car and then restart it. Back with Audi getting more checks. Getting very worried now that I have brought a Lemon and a half 😕

Did they diagnose the battery and the charging system, or were just guessing? If the charging system does not operate correctly, of course the battery can not stay charged.

Who knows, Audi say they spent 6 hours initially diagnosing that the battery was at fault. Took it back to the dealer for more checks, still couldn't tell me anything concrete, just second guessing thinking it's the alternator having problems charging the battery, want to charge nearly $4k AUD to replace it. It really is a weird one as I took the car for a 20km drive today, roof down and media system playing, no 'Battery Weak' messages whatsoever, just so random.

So I am still getting battery weak messages and decided to go and buy a volt meter to do some fault finding of my own however on the way home the battery got to the point where it was so low that I started getting a gearbox malfunction message so I immediately pulled over and turned off the engine. When I tried to start the car again it was dead. Ended up Calling roadside assistance to get the battery jumped started so I could get home. He checked the alternator and it was showing 13.07v so it looked to be charging. I got the car home and again checked it myself, it was showing around 13.24v. So later in the day I decided to have another check to see if there was any drain. Initially the battery was showing 12.04v before starting the car. After starting it, I noticed it dropping gradually below 12v, it got to about 11.87v which to me indicates that the alternator was not working or not turning, however about 30 mins later I checked again and it was again working as the voltage had gone up to 13.24v. Literally just checked 30 mins later and it has dropped to 11.48v. Now I'm stuck between thinking it either being a faulty alternator (or a faulternator) or the pulley is loose/worn. Any thoughts or suggestions? Thanks all

1st battery should be charged with a good battery charger of 10 amps or more. When charged it should read 12.6 volts or better. When you start the car the alternator should read 13.5 - 14.5 volts. anything less is an alternator problem. The alternators function is to maintain correct battery voltage . Also after you charge the battery let it sit for an hour then read it again. It still should be 12.6 vo or better and if not the battery is bad.

Hey Jagtoes, thanks for the reply. I have ordered a Bosch C7 (7 Amp) battery charger which is supposed to be decent and able to charge AGM batteries, once it arrives will charge the battery as it is definitely low and as you suggest see if it discharges after an hour or so. I also did some more testing to see if there is anything drawing current from the battery whilst idle. I noticed the car starts off drawing around 8.5A initially, it then gradually starts dropping and ends up at around 0.03A which looks to indicate it's OK, however I have not left it connected see if there is anything that decides to wake up and draw current, that will be another test after the battery has been charged. I also purchased an ODB Eleven Pro which I have to say has been fantastic in seeing if there are any fault codes relating to power management (There have been some relating to rear camera calibration as well as others which could be related to the low battery) and monitoring the alternator. It has been showing 13.2v when it decides to work which is definitely low. Will keep you posted once the alternator is replaced and the battery charged. Thanks all for the help so far.

Hey, interested in hearing what was the solution in the end - was it the battery or the alternator?

Hey there, it's still up in the air am afraid. I ordered a new Alternator from the US as everything in Aus is SO DAMN EXPENSIVE, except it did not quite work out how I wanted as it arrived with the Positive terminal pushed in, tried it out and it did not work. I took the car to a local Alternator specialist who says he can rebuild my original one so going down that path, just waiting for a new regulator. I definitely don't think it's the battery as it holds charge fine and there seems to be nothing draining it . Will keep you posted.

Sorry to hear about your situation, I've been in your shoes regarding a broken alternator and the disgusting expense to repair it. Hope all goes well and you get it sorted soon!

Hey there, sorry to hear about yourAlternator pains too. The joys of owning an expensive car. What issues were you facing if you don't mind me asking? Battery not charging?

My alternator issue goes back a few months, thankfully it's serving me fine now ever since I got it replaced. The alternator wasn't charging the battery sufficiently, I first noticed it whenever waiting at traffic lights, the headlights and interior lights would dim slightly and eventually it got worse to the point that the red check battery light started appearing if I stayed stationary for too long. The alternator, when the car was idle, wasn't providing enough output power to charge the battery but worked fine as long as the car was in motion.

Took it to my regular mechanic who always gives me a no-bullcrap assessment and told me straight the alternator needs replacing, had it sorted within a week but I'd been neglecting the repair for up to a month before since I wasn't sure what the issue was.

Thanks for letting me know. Hmmm, that is interesting. I am not getting any warnings about the alternator or battery, which does have me a little worried to a certain degree. According to the manual it should display a red battery warning light but that is not there. Fingers x'd it's nothing more serious like a faulty ECU or something else.

I'm fairly certain that in 2011 A4's the warning you get is the "weak battery" warning on the central console rather than the red light, so if you've gotten that then you should be all good, your ECU is detecting faults fine.

So the Alternator was rebuilt with a new regulator, so far so good with it not giving intermittent voltage, but I wanted to know if 13.4v is OK or not enough as that seems to be the current being output by the Alternator. The mechanic said it's computer controlled so it should be OK.
What voltage are others getting? Guess it will differ from car to car but just a little bit worried it could be a little on the low side. Wondering if I should have got a new Alternator instead and put the $600 AUD spent towards that - guess time will tell.

A fully charged battery should be 12.6v or above, with the engine running it should be around 13.5v so I think you're good. I'd say continue to monitor it for a week or so every second day to see if anything changes, if you see it falling below 13v with a running engine then you have something wrong.

Thanks a bunch. Will definitely be keeping a constant eye on it. OBD Eleven Pro does not seem very accurate at showing the output as when the car is running, the battery voltage gauge within the app shows 12.78v but when I put the volt meter on the terminals, it shows 13.4v and that is at the front and not directly at the battery which sits in the boot (Or trunk).
Really appreciate everyone's help and advice. Fingers crossed I won't be updating this thread anytime soon 😊

As simple test is when you go out to the car in the morning take a voltage reading at the battery before you start the car. If it is lower then 12.6 volts you have a battery problem. either it needs a full charge or it is failing.

Thanks, I just had a quick check now and the Battery showed 12.57v checking front and back which I believe is OK. I'll check again in the morning when the car has cooled down.

OK but if you just shut the car down that would be the residual charge after a drive. You now need to check it after it sits for 3 to 8 hours or so. Even if there are systems running in the background with the car off it should not affect the state of charge. Usually after I do a shut down on all of my cars the battery voltage is around 13 to 13.5 volts for at least 2-3 hours.

Hey Jags, that was around 3 hours after driving the car. I'll check tomorrow as well 😉

Oh OK so tomorrow it should be about the same..

Hey Jags and all, So this morning the battery was showing 12.42v before firing up the car which is a tiny drop from last night but then as you mentioned could have been residual and the Alternator was cranking at 13.4v when started. Good? OK? Bad? Charge the battery?

Sounds good . Keep n eye on the voltage. It shouldn't go below that 13.4 during normal use whether at idle or during driving.

I want to scream! The intermittent power issue is back! Decided I would take the car this evening for a spin, started the Engine and connected the OBD scanner to check all was OK, the voltage was showing 11.1v!!! Got the volt meter out and there was nothing showing from the Alternator, was at 11.2v on the battery terminals. Stopped and started the car a couple of times, on the 3rd attempt the Alternator kicked back in and started showing 13.4v again. When I got home and turned the car off, the battery was showing 12.5v. I am seriously at a loss here. Does the Alternator have another issue? The mechanic checked the diodes which were OK and there is a brand new regulator in there.
I did notice that idling rpm was quite high compared to normal. Was around 1300rpm and did not drop after a short while as it normally does. Also there were some fault codes which appeared when I performed a scan, not sure if these have happened as a result of the low battery:

OBDeleven data log


Date: 2019-07-26 20:30


VIN: WAUZZZ8FXBNxxxxxx
Car: Audi S5
Year: 2011
Body type: Cabriolet
Engine: CAKA 245 kW (333 HP) 3.0 l
Mileage: 65010 KM


---------------------------------------------------------------
01 Engine


System description: 3.0T SIMOS84
Software number: 8K0907551C
Software version: 0003
Hardware number: 8K0907551
Hardware version: H08
ODX name: EV_ECM30TFS0218K0907551C
ODX version: 001003
Long coding: 011C000C240F0128


Trouble codes:
P119600 - Bank1, sensor1, heater circuit Electrical malfunction
Active
P119700 - Bank2, sensor1, heater circuit Electrical malfunction
Active
Date: 2019-07-26 20:09:11
Mileage: 65018 km
Priority: 2
Malfunction frequency counter: 1
Unlearning counter: 255
Engine speed: 822.00 1/min
Normed load value: 9.8 %
Vehicle speed: 0 km/h
Coolant temperature: 36 °C
Intake air temperature: 20 °C
Ambient air pressure: 1010 mbar
Voltage terminal 30: 11.070 V
Dynamic environmental data: 209628117D1911DC1311D171110E0211DE02120408
P013500 - O2 Sensor Heater Circ.,Bank1-Sensor1 Malfunction
Passive
P119700 - Bank2, sensor1, heater circuit Electrical malfunction
Passive



The strange thing is I started the Engine this morning just to check all was OK and the battery was showing 12.4 volts and the Alternator was showing 13.4v.



Any ideas before I drive the car off a cliff?


Get Outlook for Android

Have you checked the alternator pulley? That's what went out on mine, but the car told me so (sort of) with a charging system fault message. It knew the alternator was not producing output. Possibly yours is starting to slip.
If you put a wood or plastic item through the grill to block the movement of the fins inside the alternator, you should not be able to rotate the pulley in the clockwise direction (the direction it spins when the engine runs). It should lock up when pushed in that rotation so the alternator spins. You should be able to freely spin it in the counter-clockwise direction (the relative direction it's traveling vs the alternator rotor. It does this so the alternator can spin down slowly and not be a drag on engine deceleration. Helps longevity and efficiency.

You might want to look at the generator stats in measuring block 16 (and 17 maybe) of the CAN Gateway (where the battery stats are blocks 18 through 20). See if it supports the idea of no current flow present.

"Got the volt meter out and there was nothing showing from the Alternator" Let's go back to this statement. So you were checking the voltage across from the (+) post on the back of the alternator to the (-) negative jumper cable post on the strut tower and it was reporting 0v? Because you should have seen the same voltage as from the battery to chassis ground. 0v implies you have some open circuit where that alternator output cable goes to. Maybe corrosion on the other end?

Your DTCs are regarding both your pre-cat O2 sensors, saying the heater circuit has failed. This typically means it's time to change them. Mine went out around 85k miles. But, unless you're been ignoring that one was already bad, for both to go out at the same time, .... I'd clear DTCs and see what comes back after a few drive cycles.

You have an S4, not an A4, so I have no wiring schematic assistance for you.

Hi SMac770, thanks for the information. Sorry I should have mentioned that this is an Audi S5 3.0T Cabriolet, same engine as the S4 I believe. When I mentioned the Alternator not kicking I was assuming that from the 11.1v when touching the battery posts. The Alternator on this car is right underneath so I cannot read the voltage without hoisting it up so I'll need to take it to the mechanic again. The mechanic says he checked the pulley, diodes as well and checked all the voltages. I'll ask about the pulley again. I'll clear the faults and see if they come back.
Could the Oxygen Sensor be causing an issue like this? Reading online it mentions that if it is faulty it wont close the curcuit and could cause battery drain.
This morning the battery was at 12.1v with the car not turned on, potentially from stopping and starting the car twice in the space of a few mins yesterday.
Thinking to go down the path of changing the O2 sensor first before going back to the Alternator. Definitely a cheaper option. Thoughts anyone?

So this morning I started the car and the volts output on the battery terminals was 11.4v. I did notice that the car was idling at 1500rpm for some reason. Once I turned off the car and turned it back on, the idling dropped to under 1000rpm and the voltage on the battery terminals returned to 13.4v. Would a loose Alternator pulley cause something like that?

Loose is not the term I would use. Slipping seems more appropriate.
Do you always have to double start the car to get alternator output? Is it any different when cold after sitting overnight vs still warm after only been off an hour or two?
If you think the O2 sensors might be relevant, just unplug them and see how it goes. The car won't run optimally, but it'll run.

I imagine it'll be a tough troubleshoot. When it's not charging, you cannot visually inspect the alternator nor take readings right at the alternator.
Taking readings at the + and - jumper cable posts in the engine bay should yield same results as those across the battery posts. You might find those easier to access regularly.
But you really need to be able to test the voltage at the alternator output when the issue is live to see if it's in fact no output or a voltage loss somewhere along the way that's occurring.

A few interesting videos, though not necessarily your problem.
Just a curious video showing how the cause could be somewhere completely unrelated: www.youtube.com/watch?v=vDwbX84sc8k
Very interesting video showing how thermal buildup from a bad connection causes significant voltage drop on the way from the alternator to the rest of the car: www.youtube.com/watch?v=TJl-wyZO87c

Has the mechanic had the car in the shop with the issue live? Has the alternator output post been monitored when the issue was live? Or is it just assumption? That at least puts the issue at the alternator itself vs an issue downstream.
I don't know what it could be that would cause the charging system to not work and then work unless it was a poor connection that closed the gap with some thermal expansion. But it would do a lot to know for certain if the issue is with alternator output vs delivery of the alternator output to the rest of the car.

Thanks for this information. That is the hard part, getting it on a ramp whilst the issue occurs. So far it has happened when the car is cold, once the car has warmed up it seems to be OK however it's too soon to speculate as before the Alternator was rebuilt it would happen randomly whether warm or cold. Just checked the voltage on the terminals whilst the car is off and it is sitting at 12.18v. If it does drop again will scan and see if it reports the Oxygen sensors again. Do you know where they are located? Will it cause any other major issues disconnecting them? Thanks for your help so far.

Being an engine not in the A4, you might find better guidance about the O2 sensors used in that motor in the S4/S5 forums.

I find these videos about the 3.2L V6, which is the same engine family as the 3.0T supercharged.
www.youtube.com/watch?v=waSGbrbWVk8
www.youtube.com/watch?v=9WKq5aIN3Yg
If you can find the plug end of the cabling, you could test the heater circuit resistance if you can determine the two pins for the heater circuit. That would give credibility to the DTC claim of a heater circuit problem. But I don't know the pin out or wiring to know which of the 6 pins are the two heater circuit pins. Damn, the S4 sensors are not cheap.

I was surprised at how there seems to be not much about the 3.0T supercharged out there. And what is there makes me love that I only have to work on a 2.0T.
www.youtube.com/watch?v=xyZLjJOxBvQ
www.youtube.com/watch?v=KiGo_2VF624
Wow, what a packed house mess in there. I can't imagine what the 4.2L V8 in that same engine bay was like to deal with.

https://cimg6.ibsrv.net/gimg/www.aud...1f09532feb.jpg
Battery voltage and Amp usage when the Alternator does not work.

https://cimg8.ibsrv.net/gimg/www.aud...64e8328491.jpg
This is the Voltage on Terminal 15 and 30 when the Alternator is not working.

Thanks for the links. So I spent the day with the car, and the issue is pretty much the same as before so it is definitely not the voltage regulator. Regardless of whether the car was hot or cold the intermittent voltage occured. It would take 2 - 3 attempts of stop/starting the car to get the correct voltage displaying and the Alternator to work.
The more I think about it the more I actually think you could be right about the Alternator Pulley slipping. I think I will go down the path of a new Alternator - wasted enough time and effort.
I also monitored the Oxygen Sensors whilst the wife was driving and the voltage looked OK on Banks 1 and 2. Will have to measure them in the morning when the car is cold. Will keep you posted.

So took the car to the mechanic when the issue occurs, Alternator was receiving the correct voltage of 8.5v but only putting out 11.35v. Has to be a dodgy alternator in that it randomly occurs, unless anyone objects? I am seriously hoping it is nothing else, cannot afford to spend any more money on it 😕

https://cimg2.ibsrv.net/gimg/www.aud...d74a91a1f4.jpg
Hey All, just thought I'd give the latest update in the Alternator Saga. So my mechanic replaced the Regulator on my existing alternator, unfortuntely the same problem occurred. They started to think it was not the Alternator causing the issue. Just to be on the safe side and not to waste $2000 AUD on a new one, I got another Alternator from the UK for $200 delivered and tested that, unfortunately the same issue occurred again.
So after scratching his head the mechanic removed the regulator cable and tested it, low and behold the issue no longer occurs, the Alternator from the UK is outputting around 14v regularly, when the regulator cable is plugged in it causes the issue to occur so there is a potential short somewhere.
The mechanic has left the regulator cable unplugged - he took it for a long drive and the issue did not occur. I have taken it for a test drive and the issue has not happened. I did an OBD scan and there are no faults showing. The million $ question is what issue could it cause leaving the regulator cable unplugged? Where is that cable connected to? The ECU? Any thoughts? Happy that the issue is not there but at the same time concerned it's going to cause something else to happen. Thanks for everyone's help.

You or your mechanic should trace the wire back to it's source. There is a problem in the harness which may show up in the future and leave you stranded. Also driving without this being connected may cause another issue. Look at it this way , if you don't need the wire then why was it there since the car was made.

Should be a blue/purple wire on pin 1 (no wire on pin 2). This goes to T17r pin 11 in the ECU box (the white plug).
It's a LIN bus connection going to J367 (battery monitoring control module) T2x pin 1 (I think this is the two-pin plug on the "box" that is sitting at the negative battery post)

It also carries on to T17e pin 15 in the ECU box (one of the red plugs) and then on to J533 (data bus on board diag interface) T20d pin 2.
If you have stop/start, then apparently also to J532 T12aa pin 1. J532 is some kind of voltage stabilizer. We never had stop/start on B8 here in the US, not till B9. If you have that, it'll certainly complicate things.

So it's not a simple voltage wire, but apparently a LIN bus comm wire, with the other two involved devices being the J367 and J533. Assuming there's not an issue with the wiring or plugs.
The J367 is on the negative post of the battery, the J533 is in the dash mounted to the side of the center vents (remove glove box and it should be clearly visible.

I think I'd plug the voltage regulator back up and disconnect the battery monitor plug and see if the issue stays away. That would point to a problem with the battery monitor.