03 Buick lesabre o2 heater circuit

So I had a lasabre come in about a week ago with check engine light. It had an evap leak which was fuel fill tube. Replaced fill tube cleared pcm & ran evap test with scanner, all good. Test drove & got down to 3 i/m monitors not ready. He stopped back 6 days later & 327 miles later and evap & o2 sensor heater circuit not ready yet. No. Codes. Then the next day had an 02 ram 1500 4.7L repaired check engine light, cleared pcm ( he's past due for inspection) he drove over 500 miles, still has o2 heater & evap not ready. Why do things go in streaks ? Any thoughts?

Update. Got ram heater monitor through this am. Took 30 minutes of cold start idle befor it went through!

Wow, that's kinda surprising... Most GM's complete the O2 Heater right away.

Next time you get a hold of it, watch the O2 signals KOEO. See how long they take to pull down from 450mV to less than 100mV. That's the classic GM heater test. The heaters themselves aren't monitored, so the PCM uses the O2 signals to judge heater function.

Here's an example of a K1500 I saw recently. It was throwing a code for the B1S2 heater, which got replaced. You can see the difference in how far and how quickly the new sensor pulls the bias down compared to the other sensors.

It is weird how things come in spurts like that. You won't seek certain model car or a specific repair for a while and then all of a sudden you will get several with in a short period of time

Thanks for response Bruce. I agree seems like things go in spurts! I haven't got the Buick back in again yet but would like to try the same procedure on that. Chrysler pcms have always seemed to be much slower to me. I just decided to try a long cold start idle & it actually worked. This business is all about learning everyday. If it were easy we'd all be doing something different

The weird thing is I even tested all o2 heater aspects on the Buick & the ram n everything was in specifications

Hey Tyler, will that test work even after engine already warm ?