1992 525i O2 sensor relay coil wire has 12V and the switched groundfrom DMEis good. As soon as I connect the O2 relay the input power for the coil disappears, thus the relay is unable to function without the coil. I can jumper the relay to provide power however always hot-12V to the O2 sensor/heater but the check engine light goes on. Is this normal during initial startup, because the book says its an open loop during startup, then does the DME pulse the swithchedground to energize the relay during idle. Is my DME bad If I do not get power at operating tempt. to the coil relay?

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I have to go by memory, I haven't worked on a 1992 525i in a while, there are very few left around here.

The o2 heater relay will be activated immediately after starting. It should run when the engine is on to maintain oxygen sensor operation.

What are you trying to fix, fault code or symptom?

- Nick