Fault code U1520

The car is in Sweden.

I have had trouble with
The code 54 water in the diesel filter.
even though I have not had any water in the filter or tank.

and I have tried to remove the negative battery pool
to see if the code U1520 disappears but it will return after a while.


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Interesting......you folks are getting a entirely different terminal design and I rather like the cables being bolted to the terminal.
This design, however, appears to have three potential ground resistance points.....all easy to service.

So, to get it out of the resistance path, I'd remove and wire brush all of the terminals and eyelets attached to the terminal clamp as well as the clamp to post interface and, if you can get to a few of the terminals at the other end of the cable, clean those as well.

Since the negative is off, freshen up the positive as well.

Beyond these suggestions, if not successful, you may have a internal problem with the bcm itself......something along the lines of a cold solder joint that would require replacement of the unit.
Since your car is not U.S. spec. I don't know the component location but once you find it, remove the multi wire connector and see if there is any corrosion visible (white powdery looking) on the male/female pins. Sometimes, the act of removing and reinstalling the connector will clean the connections and you can carry on.

Regards,
Rob

Here's a description of what happens to the car and when the code U1520 comes up.

We can start by removing the negative pole on the battery, then the car resets.

puts back the cable and turns on the ignition no code. starts the car and stops it.

If the car starts again after a while, turns on ignition, the car does its system control, then the code will come up.

But I would turn the key directly to start without ignition, so the code will not come up.

So what could it be?

low volt on the battery?

ignition?

fuel pump?

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