lastone

Sad to be a newbie here and have to start with a b1tching session as first on topic thread.

On a relatively cool (-37C) morning, wife's '15 refused to crank at all. Instrument cluster displayed a flashing glow plug light and turning the key did diddly squat. After four hours in the sun, everything worked normally. Wife took car (with less than 1k kms on it) to dealer, and she says they did not sound surprised with the complaint, but offered no explanation as to why or how common.

I have not had time to hook VCDS up, nor I have to admit time to even learn the Can bus version I recently bought, and dealer did not give her the information regarding codes set - if any at all.

So, two questions:

1. has anyone (or how many "ones" encountered similar problem(s)?

2. What is the cause and the fix (more than a bit upset that I even have to ask such a question with a new car)??

One thing I have learned from over 50 years of fixing VW's screw-ups is that they are remarkably consistent and pretty much EVERY car will at some point have the same problems. And, of course, they will never admit to making any mistakes.

dreadlocks

I'm not surprised a 4 year old battery would refuse to do anything at nearly the point where Celsius and Fahrenheit intersect.. diesels have many things working against them on very cold starts:

• Diesel Compression is MUCH higher than a gasser, so starters require much more amps to successfully turn over a Diesel than any Gasser
• Diesels require Glow Plugs in these temps and that requires significant electrical draw.. on a morning like you describe it'd of taken 2-4 cycles of Glow plug to even start.
• Oil Thickens dramatically and requires the starter to output even more amprage
• Batteries loose performance dramatically as temps drop, so just when your Diesel needs the most power its ever going to need to start your battery is putting out the least amount of power.

You likely need a new battery at this point, it might be up to the task on warm days but its proven its not on cold days.. You might also want some sort of pre-warming system to plug the vehicle in and pre-warm it, you can put a battery charger up at same time so the battery is also at full capacity..
You should get a nice lithium jump starter pack, keep it inside so it stays warm and then use it for extra boost on these mornings.

Good luck.

lastone

Suggest you watch the posts more carefully. I did not say it would not start, I said it would not crank. BIG difference.

You are right about the battery, but having done this for over 50 years, I would not accept a new car with a four year old battery. It was replaced on PDI. I am new to 3.0, not diesels.

Thanks for the wishes of good luck, but I don't operate on luck. I am not a gambler.

dreadlocks

If it dont crank, it dont start no?

First time it hit single digits here my 3.0L on a 4yr old battery the TDI DID NOT CRANK AT ALL.. when it warmed up it started fine, after putting a new battery in it I've had no problems starting it.. but not at the temps your reporting, it dont get that cold here.. mebe even with a newish battery it needs a lil help at those temps.

Are you certain they put a new battery in and didnt just tell you they did after they tested the original one? Did you check the voltage on that morning to see if it was even near capable of starting?

lastone

Put my conductance tester on it when I got home, was 100% when it was marginal before replacement (when fully charged).

Our '14 would crank (i.e. engage the started) at -43. Wouldn't start (not heated, just tried out of curiosity). Never any issue with ECU sending power to where it was supposed to go. VERY interesting what you experienced. Once again: did it make any attempt to engage the starter (panel display very different from no effort - which left a flashing glow plug light - and no such status to be found in the operators manual).

dreadlocks

I had a dead cell internally so it was only good enough to actually fire starter with remaining cells if it was warm and recently driven, on really cold mornings it wouldn't even try to turn over holding push button, I was seeing other issues like rear hatch not opening and MMI always doing a fresh boot indicating it crapped out.

It does seem to have various low voltage lockouts, I'd be curious what a little voltage monitor you plug into 12v plug read when you got in on that morning.. maybe glow plugs couldn't fire. I've seen those little Lithium jumpers get diesels going well into the negatives, they can dump alot of amps out and give em the kick they need.

lastone

That is what I fear (low voltage thus locked out of function by ECU), but the temp didn't even get to -30 and it started working - and I don't mean barely, it cranked like one would expect from a fully charged battery. That is why I was a bit put out that dealer either a) did not figure out (or make any attempt) what was wrong, b) tech was too lazy to record data and/or c) they knew exactly what was wrong and did not admit it (I have a friend in that store, so will in the end get the truth).

I never count on jump starts, but my normal practice is to put a 50 to 80W silicone heating pad under the battery so it is warm enough to crank and warm enough to actually take a charge on a very cold day. Wife will not allow the firewall to get punctured on this car, so will probably have to put a battery maintainer on the jumper posts. BUT: still have to figure out what to do with engine heat. If I go low watt pad on the sump, that means long time on (which is needed for battery) but I sure like the big heat from 1,100 Watt Zerostart as it means interior heat comes very soon after startup,.

dreadlocks

depending on the state of charge of the battery determines what temp the electrolytes freeze, it could had been that you had just approached or passed that freezing point causing a massive voltage drop, and just a few degrees of warmth was all it needed to get back to a liquid state

a battery tender to keep the battery at full voltage or a heating pad would probably be sufficient, I dont like to count on jump starts either but at work I dont have any place to plugin so I keep one warm in my desk drawer JIC, and I needed it once this year because the car battery decided to call it quits on the coldest day fo the year again.. car is a manual and I thought I could push start it, but learned that options now off the table w/an electric e-brake.

lastone

Once a battery freezes, the process will usually crush the plate separators and the battery is seriously compromised. A fully charged lead-acid battery (flooded or AGM) will not freeze at -45C. In fact, a fully charged battery in perfect condition (as in the new one in her Q7) with an electrolyte specific gravity of 1.3 freezes at -70C. Output is nearly linear with respect to temperature, but you are right, if it freezes, it drops off to near zero. Same it true for ability to take a charge - reduces with temp but is zero when frozen.

dreadlocks

The Q7 does not sit fully charged though, due to its infotainment package, navigation and other loads it drops pretty quickly before it shuts em down.. I have dash cam wired up with a low voltage disconnect wired up and it dont run for very long before the battery hits 70% and camera shuts off.. if a battery @ 40% SOC can freeze at -26C its possible your resting SOC ~60-70% was approaching those temps and not really frozen solid enough for damage, just a theory though.