Thanks for your attempted explanation Russ but I'm afraid it's not clear.
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Originally Posted by BigRuss
Why then does replacing the EMS ECU correct the problems?
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The EMS?
I think you mean the ECM don't you?
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The Can-bus does indeed have a direct link to the operation of the ... HRW
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How?
The HRW relay is controlled by the BCU which has no CAN bus connection.
This is how the HRW works (on my KV6). The on-off button provides an earth to the BCU (C0662-5) which in turn energises the HRW relay (C0660-14). The elements supply is directly from the battery.
When the external temperature is below 10°c the BCU uses that data (C0660-18) provided by the IPK on the K bus (C0230-3) also to energise the HRW relay. The IPK converts the external temperature sensor analogue signal (C0233-4) into digital for transmission on the K bus.
Your mission Russ is to explain how the CAN bus allegedly fits into that straightforward scenario!
Simon