No power to o2 sensor heater from relay.

[chopper35nj]

  Got the 5v between B and C positions on the plug but no voltage to A. The relay is tested and good including resistance. 12v from the 86 terminal to 85 but the relay isn’t switching while in the system, so, no power to 87a. What is the power source to the 30 terminal? Or am l looking in the wrong place. 

[dvitha]

I would clean the connectors real good on your heater relay. I have even cut it out an put new relay wiring in, for bad cases. The ECU sends the signal to turn relay on when the engine is below the temp threshold. When Idling and when the day is cooler are some of the times the ecu sends signal to turn heater on. The o2 sensor needs to be up in the 1200 degrees area all the time to work right.

[cruiser54]

Terminal 30 gets it's power from the ignition switch. 

[Ωhm]

O2 sensor/O2 heater voltage is supplied by the NC contact (87a) from the O2 heater relay. This assumes terminal 30 gets power from the ignition switch and the O2 heater relay is functioning properly. The only time the ECU will pick the O2 heater relay is during a WOT condition. When picked (during a WOT condition) the O2 heater relay will switch O2 sensor/O2 heater voltage to the fuel pump bypassing the ballast resistor.