fuse SB29

[saxontdi]

2012 Passat tdi, battery hooked up backwards. Now this fuse blows when the battery is connected. Could it be a short in the alternator? What should I be checking?

 

[VernK]

Apparently SB29 is one of two 40a fuses for the "Vehicle electrical system control module"

Doesn’t sound good.

Yours
Vern

 

[saxontdi]

I am hoping it is just a shorted wire from the battery being hooked up backwards. I bought the car this way so don't know much history.

 

[oilhammer]

That's the BCM, under the dash, above the pedal area.

Are any other fuses blown? What about the strip of fuse links at the front edge of the underhood box?

 

[saxontdi]

No other fuses are blown and this one blows as soon as the battery is connected. I haven't check the fuse links yet. Hopefully they get checked today

 

[oilhammer]

SB29 feeds a big yellow/red wire directly to the J519 module (the Body Control Module, sometimes still called a Comfort Convenience Module) under the dash, to pin 42 of the T52c connector. There are three connectors on the BCM; black, white, and brown. The T52c is the brown one.

But this may not help you, as the BCM uses several different fused feeds input for a variety of different outputs, and they are not broken down in the wiring diagram as to which is for what. It could be something on the output side, it could be the BCM itself.

What you might do, is unplug that connector, and see if your dead short goes away. If it does, then you know the short isn't in the wire TO the BCM.

Next would be to try and depin that wire, so you can plug that connector back into the BCM, and see if you can communicate with it and see if it can give you any clues.

 

[saxontdi]

Ok thanks oilhammer. Will check that out.

 

[saxontdi]

I tested the fuse recepticle. Dead short to ground. Disconnected the yellow connector from the idiot box under the dash, no dead short to ground.

Short is in the under dash box. That is the bcm, correct?

 

[oilhammer]

Yes, it is. I think I have one NIB, if you are interested in giving it a try. However, it could be something on the output side (after the BCM). Have you attempted any communication with it?

 

[06bluebeetletdi]

51CF3F43-5E19-4704-99DD-D889C26D5506.jpeg

• 06bluebeetletdi
• Feb 19, 2022

Does your 2012 have a main fuse under the hood? Like the one shown above?

 

[saxontdi]

Found the problem. BCM is a little fried. I will post pics is someone tells me how.

 

[saxontdi]

This is the part number, 5K0937087Q. What other numbers matter when I am looking for one?

 

[nshrose]

Did you ever get the Central Electric Control Module swapped out?