I have replaced all of my O2s with new Bosch sensors. I am having one sensor that was fine, but now when it will go unresponsive after driving for a few minutes. The Downstream passenger side sensor is responsive when I turn the truck on and while its idling in the drive way. It will work for a bit (maybe 5 minutes) once I start driving. Then it goes flatline and doesn't come back on. Eventually I will throw a code for it not responding.

I have ordered another, but seeing as they are $50 a pop, I wanted to see if there is something else I should be looking at for why its works some times and not others?

 

That sounds odd. It could be a wire problem. I'd first open the connectors and spray electronics cleaner in them, then put dielectric grease on the contacts, reconnect, and drive around a bit. If that doesn't fix it, then follow the wires and make sure they aren't on anything hot. I had the same problem once and just ignored it, then saw smoke coming out of the bottom of the truck the driver side O2 wiring had fallen against the exhaust. I assume that as the wire jacket was melting, the wire or wires grounded to my exhaust.

I have gotten bad, brand new O2 sensors. But getting two bad ones in a row is a stretch.

 

"... dielectric grease on the contacts ..." Just to be clear, dielectric grease should never be applied to the contacts. Dielelectric grease should be applied to O-rings, etc, that are designed to prevent or resist water ingress to the connector.

Yes, the incidence of bad O2s out of the box is unbelievably high, but real.

 

Hmm, I always put it in the 02 sensors to prevent rust, water, and oil, but I'm sure you're right. I'll quit (and quit recommending it).

 

I haven't put the second new one in yet. I thought I would check in before I did to see if there was something I should look at before I threw another $50 sensor at it. In the picture, you can see that the plug is pretty high by the transmission and loops over another hose. Is that where it should be positioned?

 

Dielectric means does not conduct electricity. We want the connectors to conduct electrical energy.

In the case of the front O2s apply dielectric grease in the cavity between the orange outer shell of the connector and the white center part (that has the actual female connectors). That way when you make the connection with the harness-side connector the grease gets pushed down to (hopefully) make contact with the black gasket in the sensor-side connector.

I too didn't understand this until quite recently. I was squirting dielectric grease directly into the female recesses of the connectors. I used electrical contact cleaner to clean them out and then started over as I described above.

 

I swapped in the other new Bosch o2 sensor and again it's unresponsive after a few minutes of driving. The wires go over the transmission. Is that right? I'm thinking the transmission heats up and causes the wire not to respond. Any one have a suggestion?

 

I just went through this.

Are you getting a click when inserting the O2 connector? In my case the harness side clicking lock mechanism was broken and not holding the connector tightly. That is why it would work after install but die after driving/vibration.

I ended up cutting the harness connector off right at the plug and using butt connectors to attach the new/used connector.

Also check that the white insert from the old O2 is not in the connector.

 

Abran
I did get a click. That's always a moment victory for my big sausage hands in those tight quarters. ��

Can you confirm that the wire should continue over top of the transmission? Is there something safe I could wrap the wires in that could reduce the heat onto the wire but not melt?

 

I put it in my spark plug wires too. They still work.

The Genesis of this bad habit was waterproofing / snorkeling four wheelers, which I used to toy with. RTV and dielectric grease were liberally applied. Overly liberally.
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I can identify with the happy click especially on that driver side connector.

I think the wires looked fine for looping if they are secure. As long as they don't get on the exhaust it should be fine.