Yes, upstream, aka pre-cat.

Yes, NTK. These trucks come factory with them and any others are iffy or may not work period.

 

These sensors, all of 'em ever made, require a good amount of heat to catalyze the chemical reaction that's the magic inside them. The PCM expects the internal heater (internal to the sensor, that is) to get the job done in about a minute, but when the sensor gets old it requires more and more heat to get it working properly and the internal heater is then insufficient. Thus the stuttering, hissing, and so on immediately upon switching to closed loop. Run the thing for a while and the hot exhaust gases flowing over the sensor will heat it the rest of the way to make it work more or less properly.

Let the thing go far enough into failure mode and just cruising along unladen, with relatively cool exhaust gas, will let the sensor cool enough to drop back into failure mode.

Now ya know.

 

Unreg, I learn more from you than any manual. Thanks for helping out.

 

You're welcome!

I'm just doin' my thing to keep the good mojo in motion -- the more you spread around, the more comes back around. This world needs a lot more of it.

 

Got it, makes complete sense now.

Thanks.