2006 Passat B6 2.0 TDI BKP - Cold start problems at low temperatures

[SilentBob]

Back towards the end of October I started having problems with the first cold start of the day, and this only appeared to be an issue when the temperature was around 8°C or less. It started off that I would hear two tones one after the other but each at a different pitch, but there was no message displayed on the dash, no code logged (checking with Carista) and the car would start and run fine. Then after a while of this some days, instead of the audible tones, the car would turn over and turn over but not start. Upon trying again it would fire straight up and would run fine. Occasionally, but not every time, this would cause a P0321 code to be logged (which I believe is quite a generic code for the ignition system). After a little while I tried waiting several seconds longer than usual after the glow plug light had gone out before trying to start and this seemed to help. It might turnover a couple of times before starting, but was still better. This was still only ever the first cold start of the day. It never happened upon leaving work but, FYI, we have an indoors car park there. As the weather warmed again the problem disappeared. I figured that this must be glow plug related due to it getting worse at lower temperatures, but was surprised that there would be no specific code reported. Due to the time of year and the fact that colder weather will be coming I decided to bite the bullet and get the glow plugs changed (this proved a bit more expensive than I was expecting due to having the related loom changed too). Due to the milder weather I wasn't able to make any judgement on whether this was successful. However, when we did eventually start seeing temperatures drop I had no problems starting. No tones and no excessive turnover. So I was happy. Until...

Yesterday morning it turned over a couple of times before starting, and then after work it was turning over repeatedly but not starting. When I stopped trying I got a single audible tone and a message saying there is an engine fault, but upon pulling the key fob out, pushing it back in and trying to start it fired up straight away again. I didn't try reading codes until this morning, but there weren't any. Again, starting this morning it turned over and over, I stopped and re-tried successfully. No tones or messages this time, and ran fine. I tried again when I went to lunch today, and to my surprise again it was turning over and over but didn't want to start until I stopped and tried again. This time it logged a single error as both "Parking Brake" & "Central Electronics" - 00446 : "Function Limitation due to Under-Voltage". I guessed that this message may have been due to too much load being taken up on turning it over and preventing correct power for other functions?

So the question is, do these symptoms point to anything obvious that I should check or change?

I am guessing that it is not likely to be the battery, else why would it start straight away on the second attempt? I have seen mention of temperature sensors possibly misreading and preventing a correct cold start. Is this likely? Coolant or fuel temperature sensor? Any easy way for me to check this? Other than that, I am at a loss as to what could be affected by the outside temperature.

FYI, other things that I have already had done on the car fairly recently should they need to be ruled out or considered...

- Cam Position Sensor : Replaced a couple of years ago I think, when I was having problems with warm starts. The cam belt (full kit) was done at the same time as it had to come off anyway.
- Tandem Fuel Pump : Was replaced about a month after the Cam Position Sensor as it started leaking.
- Clutch and Dual Mass Flywheel : Was replaced a few months ago. The release bearing had become very noisy so I had clutch replaced out of caution. Was advised that the flywheel needed doing too.
- In Tank Electric Fuel Pump : Replaced after a fairly recent breakdown (end of August). Was suggested that was damaged by debris in the fuel following tandem pump failure almost 2 years earlier.

Thanks,
Simon

[thedktor]

I had exactly the same problem and it was the battery. It would turn over for quite some time leading me to think the battery was ok, but I didn’t get round to checking it properly for a while.

With a new battery it fires up instantly, a dramatic change.

Check your battery voltage after leaving overnight – a good battery will be 12.7 V or more. A weak battery will be 12.6, 12.5V, or less, mine was sitting around 12.5V.

[SilentBob]

I had exactly the same problem and it was the battery. It would turn over for quite some time leading me to think the battery was ok, but I didn’t get round to checking it properly for a while.

With a new battery it fires up instantly, a dramatic change.

Ha! Funny you should say this. I was waiting for us to have some more freezing temperatures to be sure before posting an update, but I did end up replacing the battery and it has been fine since.

Early Christmas morning it was below zero when I tried starting the car and it did the normal turnover only on first attempt and start immediately upon second attempt. However, when I next went to start the car on Boxing Day afternoon/evening it would only repeatedly turnover without starting. After four attempts and it still not starting, and even though it didn't sound like the battery was giving up at all, I decided to hookup some jump leads to my son's 1.0L petrol Citroen C1. Lo and behold, with the Citroen just sitting at idle, my car fired up straight away. I turned my car off after a couple of minutes, and each time after that it started straight away on its own. Clearly this wasn't a case of my battery being flat or nearly flat, and there is no way the battery on the C1 would have been able to start my 2L diesel Passat. However, it did make me feel that, despite holding plenty of charge, that the cold weather was just about preventing it from delivering the power required to start and all it needed was the tiniest amount of help.

So I bought a premium battery to replace it and have had no problems at all starting since.

I did find it weird, as normally you would expect a duff battery not to hold charge and therefore to give obvious tell tale signs. That it would always start straight up on the 2nd attempt and never sounded like it was struggling to turnover made me completely discount the battery from being the problem.

[Quatrelle]

Just as a P.S. to this - years ago on a neighbour's car, the engine would spin up no problem, but not fire. We removed the battery leads, cleaned the clamps and the battery posts, connected it up and the engine fired immediately. Had something similar on my ride-on mower recently, the problem was the earth lead connection to the chassis.

The engine spinning over is the red herring.

[thedktor]

Yes its interesting to discover how some engines seem to need a very specific minimal voltage, or maybe its just newer stuff, but mine isn’t even common-rail so just assumed if it turned over, even slowly, it would start!

The battery voltage test is a useful one though as it works quite reliably and saves buying a proper discharge tester – 12.7+V good, anything less and the battery is getting weak.

[Renars]

There is no difference between common rail and PD engines on this subject as ECU gives signal to injectors to start inject fuel for both of these fuel injection types.
Low voltage sometimes prevents this from happening.

[DMitch16]

There is no difference between common rail and PD engines on this subject as ECU gives signal to injectors to start inject fuel for both of these fuel injection types.
Low voltage sometimes prevents this from happening.

With a continued crank the ECU will decide early on that it is a non start anyway possibly throwing low oil pressure and other warnings / MIL light due to low voltage detection. It is pointless to continue and multiple short attempts should be made as a long continuous cranking is pointless on these engines.