A4 2.5 TDI: Cold Start Problems & Solutions

Hello,

I could use some advice from you regarding an Audi A4.
The car starts immediately when the ignition is turned on, even when cold. However, once the car reaches a slightly warm operating temperature (around 60°C), it can only be started after several attempts. The car has 180,000 km and was manufactured in 1998. There are no air bubbles in the diesel line, and the coolant temperature sensor is new. What could be the problem?

Hi,

Either the ESP system has a fault, or the starting speed is too low... Can you measure these?
If the starting speed is too low, one could try to adjust it using the data set in the engine control unit before replacing the starter motor, battery, etc.

Best regards, Rainer.

If the engine is mechanically sound, I would suspect the pump, but I would still measure the starting speed. What does VAG-COM say? There's definitely more information about starting in the higher measurement blocks, but I can't recall the specifics right now.

Hi,

Sure, please provide the text you would like me to translate from German to English.

Fahrzeug springt bei abgezogenen Kühlmittelgeber sofort an! Ansonsten muss ich orgeln. Je länger das Fahrzeug steht, nach Betriebstemperatur,desto länger muss ich starten. Erst wenn der Wagen total Ausgekühlt ist,springt er wieder Sofort an. Fehlerspeicher ist leer. MwB 18 sind alles 0000000 gesetzt.Das heisst Status EP OK.Spritzbeginn perfekt auf 2°Grad n. OT.
Idle speed control is functioning correctly.

Conclusion: When the coolant temperature sensor is disconnected, the car starts immediately.
Otherwise, you need to crank the engine to get it started. This only happens when the engine is warm. If the car has cooled down, it starts perfectly again!

Question: I think it's a combination of many small wear and tear factors (pump, starter, etc.).

Ideally, an increase in the starting amount would be best. But so far, no one knows how such a thing would work, especially regarding the login process. (I've read a lot, but I haven't found anything useful specifically for VP44.)

Perhaps someone can help me. Thank you.

Hello Luiggi.

If everything is okay when the temperature sensor is disconnected, then the starting speed is too low.

With warmer coolant (KW), the MSG (presumably a control module) expects a higher initial engine speed before fuel injection is allowed.

Cause: Battery too weak, excessive resistance in cable connections, starter motor worn out.

Let's check the first two points first. If that's not the issue, I would consider replacing the starter motor, or having Rainer adjust the data set in the MSG (Main System Generator). You can have several things adjusted at the same time, not just the minimum speed before injection based on temperature. And the price difference between that and a new starter motor might not be significant.

It's all explained in the article, though.

Regards,
Guste.

Hi,

I replaced the battery again today. Unfortunately, it didn't work.
Would it be possible to change the minimum speed (e.g., through the engine control unit using diagnostics)? Can I change this myself using VAG_COM?

Hi,

luiggi wrote:

Würde das gehen,die Mindestdrehzahl zu verändern? ( Also Per Diagnose im Steuergerät )? Kann ich das mit VAG_COM nicht selber ändern? Mfg

Unfortunately, I can't. Since the minimum speed depends on the data set, it would be helpful to know the VAG part number and the software version of the control unit, and to check the engine's revolutions per minute during the start-up attempt using a diagnostic tool.

Then I can check to see if that might be the cause or not.

Best regards, Rainer.

Hi,

I don't have access to the vehicle at the moment. As soon as I do, I will post a car scan here.
"I noticed that the engine is most difficult to start when the vehicle has cooled down to approximately 50-60°C. (I only needed to run it for 2 minutes, and then I could barely start it again?)"