2.0 TDI CBBB: Engine Stalling & No Start?

Dear diesel mechanic community,

For the problem described below, I would like to ask for your input and ideas.

My wife's car broke down yesterday while she was driving and won't start again (the starter motor is turning, but the engine isn't starting).

Here are the things I checked yesterday evening that didn't work:

* The only error code stored was P2015, but it had an older mileage reading associated with it. This error relates to the intake manifold flap. The intake manifold flap, or swirl flap, controls the airflow (but does not block it) in the intake system, and as far as I understand, it doesn't have the potential to cut off air supply to the engine. The error code could be cleared, and it didn't reappear during the starting attempts.

* The throttle valve (not the intake manifold control valve) can be accessed and controlled via actuator diagnostics. The actuator motor has moved, and the sensor values have been registered – so it should be working correctly in that regard.

* I was also able to activate the pre-lift pump in the tank and fuel pump 2 (not the high-pressure pump) using VCDS (a software program for bleeding/filling the fuel system). The program ran for several minutes. Both the pump in the tank and the one in the engine compartment were audible.

"During the starting process (while the starter motor is engaged), I observed the values on the high-pressure side of the fuel system. They fluctuated somewhere between 280 and 380 bar. I don't have any reference values for that. The VCDS help popup mentioned something about 200 bar at idle, which would be at least in the right order of magnitude. When the starter motor is not engaged, the pressure slowly decreases."

Sure, here is the translation of the text from German to English:

"Additional information:"

* The problem occurred on approximately February 28th of this year, at a mileage of about 319,750 km. At that time, there were no error codes stored (none at all, not even P2015). Currently, the odometer reads approximately 323,000 km. Back then, I didn't perform any systematic troubleshooting. The vehicle eventually started after a very long cranking period and has been running without issues since then.

* When the error first appeared in February, the tank was almost full (probably driven about 100 km since the last refueling). This time, the tank is almost empty, but not yet on reserve (approximately 1000 km driven). Therefore, the fuel level apparently plays no role.

* So far (this is not a reliable statistic), the error has occurred shortly after starting the vehicle (cold start), typically within a distance of less than 1 kilometer and a driving time of less than 2 minutes.

"My wife thought that recently (without specifying exactly when), the fuel reserve light came on for a few seconds and then went off again."

* The diesel filter is relatively new (replaced in August 2020 at approximately 307,000 km; the replacement interval is 90,000 km, and the air filter was also replaced in August 2020).

Currently, the car is parked on the street. Therefore, I can't test any larger components of the fuel system that could potentially leak. What would be the next steps to take, or are there any known issues that could cause this type of problem?

Bye.
peace

Hi.

Is the engine control unit (ECU) detecting that the fuel tank is empty?

Is the diagnosis running continuously and without any problems on the engine control unit?

Best regards, Rainer.

Hi there,
Another possibility is that, despite the fuel gauge reading above zero, there isn't enough fuel left in the tank.
What model/year are you driving? After the very old SSP420, a minimum pressure of 120 bar is required for the starter to engage.
hg
Herbert.

Hello,

First of all, thank you for the feedback.

dieselschrauber wrote:

Is the engine control unit (ECU) reporting that the fuel tank is empty?

Hmm, I need to check if there's a data block for the fuel level - probably it's more likely to be in the instrument cluster than in the ECU, right?

dieselschrauber wrote:

Is the diagnosis on the engine control unit running continuously and without problems?

I've only had this car since August 2020, so there isn't much experience yet. The biggest issue I've had with diagnosing the engine control unit was related to the throttle valve actuator motor. I experimented with different engines and also adjusted the throttle valve settings. However, there were no anomalies like misfires or contact issues. Also, reading error codes and performing actuator diagnostics has always been unremarkable so far.

Herbert wrote:

.. despite the fuel gauge showing above zero, there is not enough fuel in the tank

. It's possible, but it doesn't fit with the first occurrence of the problem when the tank was almost full. Also, based on the mileage and previous average consumption, it's rather unlikely. And ... see at the end of this message. I do want to take a look inside the tank anyway, to see if anything is heavily contaminated or similar...

Herbert wrote:

Which model/year do you drive?

Passat 3C, B6, model year 2010 - that's my wife's car.

Herbert wrote:

at least 120 bar for the start release

Okay, then the displayed values are initially well within the acceptable range. Are there any empirical values that indicate whether the above pressure values can also be achieved if, for example, the fuel supply from the direction of the diesel filter is not correct, or if there is air on the high-pressure side of the system?


The good news is that the vehicle is running again for now. During yesterday's test, I checked the crankshaft sensor readings during the starting attempts. They fluctuated between 184 and 206 revolutions per minute. That seemed a bit low to me from memory, but actually, the starter motor didn't sound unusually slow.
After that, I connected another vehicle with its engine running to jump-start my car, to see if the crankshaft speed would increase during starting. Surprisingly, it didn't; the RPM remained exactly within that same range.
Since the donor unit was already connected, I kept engaging the starter motor for a while - after about 30 seconds (estimated), the sound of the starter changed slightly (becoming more even), and shortly thereafter, the vehicle started up and ran normally.
I also managed to find out from my wife that the engine didn't just suddenly stall; it sounded like we had put the car in the wrong (too high) gear beforehand. I don't know if this indicates a lack of air, a fuel shortage, or something else entirely.

Now the question is, when will the next failure occur? It won't resolve itself. But I still lack the right approaches to determine what meaningful actions could be taken.

Bye.
peace

Hi,

I mean to say: If the engine doesn't start, does the diagnostic system still run? The keyword here is power supply to the ECU (Engine Control Unit). Without power, there will be no error entries, at best meaningless ones.

Or does the engine start up again without any problems after it has been turned off?

Best regards, Rainer.

dieselschrauber wrote:

If the engine doesn't start, does the diagnostic system run?

Yes, it does - I checked the crankshaft speed during long cranking attempts.

dieselschrauber wrote:

Or does the engine start up again without any problems after it shuts off?

No, it doesn't. There must be something preventing the normal restart.

Bye.
peace

I would look at the fuel level as seen by the ECU, or the rail pressure.

Hi there,
What type of injectors are used in the CBBB engine? If they are piezo injectors, there is a mechanical pressure-holding valve installed on the return side that maintains a back pressure of 10 bar behind the injectors. Without this pressure, the injectors lack a pressure cushion and will not function.
Ref.: SSP325. The valve is not monitored by the MSG.
Just a possible cause to consider...
hg
Herbert.

Hello,

Quick update:

dieselschrauber wrote:

Fuel level as seen by the ECU...

According to the measurement block, there were still 14 liters remaining. In the meantime, it has been refueled, and this roughly corresponds to the kilometers driven in the meantime and the amount of fuel added.

dieselschrauber wrote:

...or rail pressure

. I checked the values during the unsuccessful starting attempts; they were fluctuating between approximately 280 and 380 bar.

Herbert wrote:

... a mechanical pressure-holding valve is installed, which maintains the return pressure behind the injectors at 10 bar...

Is that the G410 in the SSP? I need to investigate how it looks on the Passat and whether there's anything to check, or if it should be replaced as a precaution.

Thank you all for your suggestions.

Bye.
peace

Sure, here's the translation:

"For documentation purposes only."

An error has occurred again. This time, the vehicle drove normally to its destination and then failed to start when the driver tried to restart it.

Date: November 15, 2022.
Mileage: 325,130 km
Fuel level: approximately 20 liters below full.
Checked: Error memory in the control module (MSG) is empty; Diesel filter housing opened before attempting to start the engine - it was full but otherwise appeared normal.

Bye.
peace

Hello.

Once the vehicle starts again, does it run normally, or do you see something like white smoke?

Create a log if the engine fails to start. Record the following values: measured air mass, RPM, and fuel injection quantity.

Best regards, Rainer.

I didn't pay close attention. The vehicle was parked on a small side road in the forest, where the air doesn't circulate as quickly. He didn't smoke heavily; otherwise, it would have been more noticeable. I will be more careful next time.

Bye.
peace