slovcan

Hi folks,

I noticed something a few days ago. First, a bit of miscellaneous info - maybe related, maybe not. It has been a bit colder this past week, but not extreme - a bit below freezing at night and a bit above in the day. In the coldest part of winter I would get the Aux Battery warning on colder mornings after colder nights. Haven't seen that for about a month or more.

What's happening now is after a 12-24 hour layover I try to start the engine and it doesn't crank at first. Specifically, I put my foot on the brake (which is hard like an old vacuum system that lost all the vacuum), push the start button and hold for a half second or so (as normal), watch the light check and glow plug light come on and go out (all normal so far), but then the starter doesn't turn. Nothing happens. So, then I push the button again which shuts the car off (even though the engine hasn't started), wait a second and repeat holding the brake and pushing the button. This time everything is normal and the engine starts.

Could this be the auxiliary battery?

Is it normal for the brake assist to go away after 12-24 hours parked?

Thanks all,
Glenn

CaliBenzDriver

That's a pretty interesting fault, good job defining the conditions. Your diesel only cranks on the second try besides glow plug being satisfied.

I don't think AUX is involved with that no crank condition. Go ahead and test the resting voltage of both your batteries with no load.
Is it near 12.5VDC?

Please scan the vehicle to retrieve the essential fault codes. There a chance this will help.

Flat vacuum brake booster: I know exactly what your saying about the diaphragm going flat in a hurry. Mine does the exact same thing... I am not impressed with my leaking brake booster.

slovcan

Thanks Cali. I should say that this has only happened on the first start of the day. It's all normal thereafter.

I can certainly check the main battery voltage, but my auxiliary battery is under the dash. When I go in after it I will replace it. It is planned, but was hoping to wait a bit longer. I'm up to my ears in a house renovation at the moment and every minute is taken from me.

I have a Bluetooth dongle and TorquePro on my phone, so I'll look for codes. Pretty sure that only does the ECU, though.

Cheers,
Glenn

CaliBenzDriver

If your scanner is too limited get a better one with "full" MB coverage...

You don't need to replace good parts.... simply use your scanner to read AUX Voltage from R-SAM no disassembly required: easy!
Same thing with main AGM and F-SAM Voltage

Scan for both active/stored faults... perhaps something will clue you in the glow module status...

slovcan

Thanks again Cali. I will try mine to see how that goes. Failing that, my friend was going to buy a VAGcom, but decided to wait and get a Delphi instead for now. We'll see what they say. I know the aux battery is toast. I was getting regular morning warnings when it was cold here and we did enough of the correct kind of driving that it should have been charged. No matter. I suspect it could be the original.

CaliBenzDriver

Yeah, you can apply the 5 year old battery rule and don't look twice... Besides AUX is charged with the main circuit voltage.

Some cars exhibit extremely poor voltage control below 12V that can promote limited battery life.
Measure resting voltage or use a dedicated battery tester to assess conditions.

pierrejoliat

I believe in a 2011, the only thing the auxiliary battery does is permit you to put the car in neutral if the main battery fails, for towing

slovcan

So, that shouldn't have any bearing on starting the engine, then. Hmmmm.

Thanks Pierre,
Glenn

CaliBenzDriver

Well yes AUX does not directly deal with glow-plug heaters but given the type of AUX, it can supply a safe base voltage to ECU . Whatever is bad you want to make it good.

The easiest is to always have good battery voltage: to crank the engine and then to drive. Nothing good comes from high currents + low voltage.

I do suspect your 2-step start may involve low voltage. At some point you're gonna want to charge your main battery as well as AUX and see how that helps your issue.

slovcan

Yes, Cali, I do need to get a DVM onto the main battery, too, best after sitting all night. It's a bit warmer again since I started this and it hasn't happened since. That's another indicator of a battery issue.

In the motorcycle world we have a saying - IATB (It's Always The Battery), unless it's the carbs. I don't have carbs.