Voltage reading coming from o2 sensor plug, ECU side? M103 in a '91 190e.

[RolandTiangco]

Ran codes on my '91 190e 2.6L after getting a check engine light and a subtle stumble at idle, and got code #17 "oxygen sensor shorted to positive or ground." I recently installed a new Bosch o2 sensor during some exhaust work, but haven't put on many miles since.

So I got out the multimeter and tested the o2 sensor connectors beneath the passenger carpet. I tested the voltage being generated by the o2 sensor. I did so by connecting a jumper wire on the single sensor-wire at the connector, and used the multimeter to measure voltage generated by the o2 sensor. I kept getting a steady reading of .49 volts no matter what conditions, rpm, or temp, which was odd. After probing at various points on the jumper wire, I realized that this reading was actually coming from the ecu-harness side, and not from the o2 sensor. I removed the jumper wire, disconnecting the o2 sensor entirely, and tested voltage coming from the harness (that the sensor plugs into) and learned that it's producing .47-.49 volts. I didn't expect to get a positive voltage reading from the ecu-side of the plug. Is this normal?

Any input would be greatly appreciated.


Roland
NYC