My truck is in my sig. I've owned the vehicle for about a year and a half now. Approx 90k miles.

I was under the truck doing some looking around. And I noticed the O2 sensors -- they *appear* to be original. I have no way of confirming this, but they look like it. 11 years after manufacture, I'm wondering if the sensors are failing, or at least performing at sub-standard. I have never had a CEL in the time I've owned the rig, and it runs well. Still, I'm curious.

Is it possible for an O2 sensor to be "bad", or failing without a CEL? Is there a means to determine the sensor(s) health?

 

Don 't know how to check them but I believe on the heavier GVW trucks they don't require the CEL to come on for poor O2 sensors or intermittent misfires.
If you had a scan tool with engine diagnostic cababilities you may be able to check them.

 

Must have a scanner to look at them. Autozone rents it for 160.

 

I had an '02 F250 with the 5.4. Had three bad coils and CEL never came on. Truck lost all compression in #7cyl, CEL still never came on. It would show codes when scanned just didn't light the CEL.

 

That is typical for the Federal OBD1 PCM calibrations. Misfires are non-MIL.