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Discussion Starter · #1 ·
Hi-I have a 03 1.8t that when it was down to 5 deg two mornings it would not start/crank. All lights were on and tranny was in PARK. After turning key 7-8 times it started. Only happened after sitting overnight and then it was fine. It has not been that cold again to duplicate the problem. I was wondering if any one else had this problem and where I might look for a solution before it gets cold again and I'm underneath in 0 deg. weather. Looking for wiring schematic for starter system or explaination of starter circuit and component locations. No signs of water intrusion into cabin area.
 

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More likely a weak battery affected by the severe cold. Lights don't take much current. Starter takes hella current.
 

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Yep, when I ran a tow truck for AAA, we went nuts on the cold days. Enough juice for lights, but not to start the car. Typical car battery will loose 50% of its power below 30 degrees (or something like that).
 

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Discussion Starter · #4 ·
It definatly is not the battery-I had 12.3 vts at the time it would not crank. I am leaning towards a connection somewhere that is affected by the cold. I really would like a schmatic of the starting system so I can troubleshoot further.
 

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Still sounds very much like the batt. Just because the volts were there doesn't meant that the amps were available to turn the starter. Batteries will give much less than their rated value in those temps. Trying to start the car would've put a load on the batt, and caused it to heat up internally, which is prob. why it started after several attempts. So, you were trying to start the car w/ the lights on?
 

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I thought 12.3 sounds a bit low.
Anyway, as others suggest... battery.
You can clean the battery posts & grounds of corrosion
as a bad ground could also cause a similar experience.
 

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Replace the temperature sensor

I had this problem 2 years ago. The car would not start on cold mornings. It would like a charm when the sun got up and warmed things up.

The problem is that the temperature sensor that feeds the interior computer read out that displays outside temperature also regulates the amount of gas that gets pumped into the carbuerator at ignition time -- the amount is different for cold temperatures versus warm.

Since the temperature sensor is busted, the engine operates by default for warm settings and doesn't adjust to the cold.

It took a foreman at the dealership on my 4th trip to figure this out. I live in Houston! And I went to two VW dealerships before someone was able to put some sense into the heads of the service associates who kept giving me the run-around.

I hope this helps.
 

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Discussion Starter · #8 ·
I'm going to bring a Midtronics (electronic conductance) battery tester home from work to hopefully eliminate the battery. The temp readout works in my dash-so the same sensor feeds info to engine ECM? I didn't notice the temp reading when it acted up. Have to keep that in mind for the next time. Not really looking forward to working on it when it becomes cold again, but I guess I will just have to wait.
 

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The coolant temp sender has two independent sensors - one for the temp guage and one for the ECM. Also, the temp senser for the ECM will not prevent the car from cranking. If it is bad, the car will still crank but may be difficult to start due to ECM providing improper fuel mixture to engine.

Battery voltage will read slightly lower (maybe a few tenths of a volt) at 0*F than at 70*F. IMHO, 12.3 volts is lower than I would expect at 5*F for a fully charged battery. Also, as others have stated available power (current draw) is significantly reduced at 5*F due to the higher internal battery cell resistance when the electrolyte is cold. So probably the combination of cold outdoor temps and maybe a failing battery are preventing the car from cranking.

As far as wiring diagrams, go here and on the left hand side of screen select electrical equipment which will take you to links of wiring diagrams.
 

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The battery tester will only do you good if you test it in the conditions that you're having the problem, and before you try to start the car.
 

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Discussion Starter · #11 ·
This is exactly what I was looking for! Thanks! I will let you Know what I found when it acts up again.
 

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My experience with weak batteries and cold is it never gets better after the first crank. Did it take 7-8 cranking attempts to start, or did you have to turn the key 7-8 times until anything happened?
 

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I had to turn the key 7-8 times before anything would happen. No crank or attempt to crank.
So it started okay the ninth time? Then, you need to check, ignition switch, starter interlock relays for the alarm system and the clutch/neutral switch, starter solenoid to see why your not getting battery voltage to the starter to crank. There's some recent threads on this. Search "ignition switch crank". Also, go to the russian link above and look at the electrical schematics to see where to check for voltage when trying to start.
 

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Discussion Starter · #15 ·
I got your link from your earlier post and have the wiring diagram for starter circuit printed out. Now I just have to wait for it to act up again. Thanks, kenblasko.
 

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no start cold no crank

I have a Brand new 06 Passat 2.0T leftover with less than 300 miles on it and it has stranded me twice, I have owned this less then 2 weeks! It has done the same exact thing you described push the key in no crank and no start, the battery is fine and the dash say VW systems and thats it. If you try it several times it started the first time and now does nothing no matter how many times you try it! I feel for you because even if they could fix this now I feel I can't rely on this car. I am a shop owner and a certified mechanic for twenty years!! I bought this car for my wife for Christmas and will be returning it for a refund on Tuesday January 2nd. She loved the car but what good is a car in this condition. This thing is a POS the lights are full of condensation (which is uninspectable in the state of Maine) and the clock continues to set itself to whatever hour it wants when your driving down the road. I have already had it to the dealer once for the headlights and they are full of water again! Sorry about the rant but, when you pay 25 to 30k for a car it should not have these types of problems in less then 2 weeks or at all for that matter
 

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Discussion Starter · #17 ·
Just an update: well it finally turned cold and I was able to locate my problems. Seems when it gets cold the battery voltage would drop to 12.2 vts. I traced out the starter circuit to the key switch (thanks kenblasco) and found voltage going into key switch but not coming out of start terminal. Aparently there is enough internal resistance on the contacts that 12.2 vts isn't enough to pass thru contacts. I took a small 12vt (7 amp) battery and jumpered my battery to slightly raise the voltage to 12.3 vts. guess what -it cranked right up. I repeated my diagnosis several times. I went to dealer with my diagnosis and they said nothing could be done because they don't have a printout from their tester for warranty. (It said the battery passes). I will be replacing the battery on my own and hopefully with the increase in voltage I won't have to replace the key switch.
 

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Sounds like maybe the ignition switch doesn't like cold weather either. It certainly seems like a bad battery but you might want to replace the ignition switch also. IIRC, it's not very expensive. There's also a thread a month or so ago about replacing switch.
 
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