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DME fault with O2 sensor heater relay (archive)
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Posted by Bill B. on January 28, 2001 at 15:25:27:

Guys, this is one of those weird ones. I just changed to synthetic yesterday, and installed new Bosch platinum +4's, took the car for a quick test drive, and got the check engine light. Came back, stomp test, 1-2-2-1, O2 sensor. Did a little snooping, and found that the sensor heater was not getting voltage. A little more checking, and the relay is not switching on and off with juice applied. I had an old relay from foglights (same amperage and voltage) that I disassembled so I could see what was going on, and plugged it in. Sure enough, no ground on terminal 85 of the sensor relay. Grounding the relay gave voltage at the sensor heater, but then I got code 1-2-6-4, O2 sensor heater relay fault.

Anyone ever experience this, or have any ideas? I don't want to drive it again until I resolve this, and I am afraid I'm looking at a new ECM. HELP!!!

Bill B.
'95 525ia, dead in the water (kinda)

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