BGW/Euro Passat Aux Heater Wiring


Veteran Member
Jun 16, 2014
B5.5 Passat
Does anyone have access to the wiring diagrams for a BGW Passat or one form Europe with the electric auxiliary heater?

I have already modified the ECU software to enable this feature, but I need to know how many relays I need/where the outputs are from the ECU.



Veteran Member
Feb 25, 2002
SW Ontario
2003 Audi A4Q 5spd 2.0 TDI 2056VK R783, 2006 Audi A4Q 6spd 2.0 TDI, 2007 A4Q 6spd 2.0 TDI
The passat diagrams do not show the actual relays and wiring, just the ecu outputs which are noted "not for canada or usa". I consulted the audi B7 a4 drawings for the rest. BPW uses the same ECU pins to control the relays.

Relay for low heating output (J359) controls a single element via ECU pin T94/71

Relay for high heating output (J360) controls 2 elements via ECU pin T94/70

The ECU grounds the relays to activate. Power for the coils comes from S282, the engine electronics fuse located in the ECU box. This is important. Due to timing issues, if you don't feed power from S282, which comes on with ECU power relay J317, you will get fault codes for the relays. They must power up from the ECU relay and not from some other source.

The relay contacts are fed directly from the battery with a heavy guage wire to a 40amp (low output) and a 60amp (high output) maxi fuse. The ground for the elements is the usual location on the "A" pillar behind the kick panel.

I would recommend heavy wiring and large relays. I'm guessing this setup draws at least 25 amps for the low and 50 amps on high, so 75 amps from the battery when all elements are on.

I have seen the whole setup with relays most of the harness and the elements on it might be wise to purchase it in this manner.