For a year or so now, I've had a crank but no start problem. If I run the car for a short trip of 5 - 10 minutes, when I try to re-start it cranks but doesn't start. It will start after letting it sit for about 20 minutes. I read the forums and checked the basics - spark, fuel, air/vacuum, etc. VAG-COM showed no codes. Then I read something about the crank position sensor and the coolant temperature sensor. So the next time it happened, I didn't have my VAG-COM so I just unplugged the coolant temperature sensor and it started up after gurgling for a second or two. Is there any way to check the coolant temperature sensor itself? I know a new one with the clip and gasket is pretty cheap, but I don't like taking random guesses and throwing parts at a problem until I get lucky and fix it. Thanks for any help!

Pete

 

I've never tried it, but I would think you'd be able to do an output test with Vag-Com. I'm not terribly familiar with it, maybe one of the guys who uses it more often can confirm.

 

In VAG-COM you can read out the temperature the CTS is sending to the ECU. There are 2 ways to do it: when in VAG-COM, first select Engine to access the ECU, then either click Measuring Blocks or Advanced Measuring Values. Either way you'll be able to find out the status of the CTS.

When the car is at operating temperature, if the value reported by VAG-COM isn't about 80-90 deg. C then there's definitely an issue with the CTS.

 

^Exactly who I was hoping would chime in

 

Thanks Metal Man and CCA4! It may take a few days to get to this, but I'll give it a try and post how it goes. I know the basics of VAG-COM, but I'm glad there are people to help with the finer details.

Pete

 

I had a chance to test the CTS this weekend, and it looked to be in good working order. I also had a crank but no start condition this weekend when I drove about 5 minutes to the gas station. No luck this time when removing the CTS. The car did start when jump started, which was surprising to me.

The starter was cranking fine without any hesitation or dying, so it didn't seem that the batter was in bad shape. I actually tested the battery a few days before and it looked fine. This time, however, when I got home I tested the battery again and the battery analyzer showed that the battery was weak/needed a charge. I charged it overnight, and the battery was reading fine again. The gentlemen who helped with the jump start said that a lot of times there's enough power in the battery to run the starter, but not enough power to ignite the spark plugs. He had seen it a lot.

I'm going to check for a parasitic draw just in case since the alternator appeared to be working fine and the battery is only a year and a half old. I saw a good how-to on checking for parasitic draws on Eric the Car Guy's Youtube site. There also may be a contact problem somewhere along the electrical path. It may take a while, but this type of thing is fun for me since I can learn more about this A4 and autos in general as I eventually figure out what the problem is.

I'll probably post a new thread since this doesn't look like a coolant temperature sensor issue anymore.

Thanks again guys.
Pete

 

One additional fail-prone part is the ignition switch. Mine was internally shorted and causing a drain as well. New switch fixed it. It's inexpensive ($25ish) and easy to install if you're comfortable messing with your airbag.

 

Pete!
I had the same symptoms in my car exact same!
And it ended up being the cts! I under stand you don't want to throw parts at your car but for the price of the temp sensor if wouldn't hurt.( i paid 9-12 bucks for it ) I got mine from my local vw dealer much cheaper than Audi for the same part!

Imthedevil could be right to. Take a meter to your battery while in the car and check it every hour or so to see if there's a drain.

And when you do start your car watch the battery gauge with the ignition on sould be around 12 when starting shouldn't drop below 9

Just my thoughts

 

And how the heck did you put up with that for a year!!?

 

Thanks guys. I'll have a chance this weekend to continue the investigation. My multimeter just went on the fritz, and I won't have time to get a new one for a few days.

Actually, my wife asked me the same question - why do I put up with it? Since I don't drive this car that often, it didn't really bother me. Usually I drive it for a short trip, it sits for more than an hour, and then I drive back home, so it never turned into a big issue. We've got a minivan that we use most of the time. The main reason I put up with it is that I love working on this car! It's almost like therapy whenever something needs to be fixed, and I just bide my time until I have a chance to get to it!

I'll keep you posted. Thanks again!!!

Pete