O2 Sensor problem

If you used an aftermarket O2 sensor, the problem may be with the sensor, especially if you had to snip and join wires.

I would do the same check on the replacement sensor to see if it checks good or bad. Keep in mind that you are checking the heater circuit and not the O2 sensor operation. If the O2 sensor heater check out OK, check the heater circuit wires back to the ECU for an open or short.

The need to snip and splice is one of the big reasons I am not a fan of aftermarket O2 sensors. They live in a pretty harsh environment, exposed to exhaust heat as well as road debris, water, snow, etc. The factory connectors are designed for this environment, while many DIY splices become the weak link. IMO, the extra cost of a factory O2 sensor is worth the reliability and with a known longevity.

Let us know how you make out!

It is not a dumb question. The way to check for a problem in the circuit between the ECU and O2 sensor is to check for continuity, basically zero resistance, between the O2 sensor and the corresponding pin on the ECU connector. It helps to have about a 5 or 6 foot long piece of wire to extend the reach of your ohm meter.

While you are checking, make sure the wire that leads into the pin on the ECU connector is not loose, and make sure the splice connection you made at the O2 sensor is good. In fact, I'd start by checking continuity in the wire before and after your splice.

Also, with the ignition off, you want to check for continuity between the O2 sensor circuit wires and ground. I doubt if this is a problem unless the vehicle was in an accident or heavily modified where wire harnesses were disturbed.

I'd look at the connections, not the wiring.

I second.

Also, the circuit operates on milivolts or some very low logic voltage like that. I don't really know or care, my point is, any problem with the connection points will translate into poor operation of the system.

This is one of those circuits that must perform to a certain level within a specific time frame, then do something different within another time frame, then report what it detects every so often -- a period of several times per second. The long and the short is that the signal is actually very complicated, and a poor connection will make the signal shape -- time and level -- be incorrect for what the computer is looking for. The result is that the signal is out of range, and the Check light will come on.

Only the sensor side operates at low voltage (0-1.1v to be precise), the heater side (that the error is) is 12v and fairly high current.