Evap, oxygen and heater monitors will not set on 2008 Chevy Express

I have a 2008 Chevy Express 2500 4.8L with 200k which does not want to set the following 3 monitors; Evap, oxygen and oxygen heater. Vehicle has been driven for 300 miles with numerous trips with overnight stays for complete cool down to simulate a true cold start.

All the other monitors are set including Catalyst. I don't have much experience with Chevy's. Is it normal for them to set a Cat before oxygen and oxygen heaters? Seems odd that a cat monitor can be passed before oxygen sensor integrity is checked, no?

No pending or active DTC's under Engine or Transmission. Battery and charging system have been tested. Fuel trim numbers at 1-6% of total correction for Bank 1 and Bank 2. Narrow band oxygen sensors monitored and don't seem to be biased or lazy. Tested with propane induced into into intake and created vacuum leaks while monitoring the waveforms. Owner replaced Bank 1 sensor 1 Denso sensor just because he "googled" it. He has the original box and receipt and we have confirmed part numbers with parts store. Compared the readings to the opposite bank and nothing sticks out.

Mode 6 examined and the oxygen sensors for both banks is Complete under the "Lo and Hi voltage switch time".
R/L Sensor Switch Time and L/R Sensor Switch Time are Not Complete on Both banks. ( What is R/L and L/R stand for?)

Hard reset has been performed with terminals disconnected from battery and both leads connected.
PCM reset with scan tool and vehicle was driven for another 100 miles. Same results: everything is complete except EVAP, O2 and HTR.

IAT, ECT, FTP, Fuel tank level sensor have been tested and functioning normal. Duty cycle heater control monitored with Autel. Evap system tested with smoke machine and all solenoids tested while system induced with smoke.

Anything else I am missing that I can check?

Look at all of your data PIDS to see if anything looks off. I remember a case study I read about a Taurus that wouldn't run all the monitors because the fuel tank pressure sensor was stuck at 4.9v.

Also look up the criteria for running those monitors. That might point you to specific PIDS to look at.

But yes I've seen cat monitors complete before O2 monitors complete. Not sure where the logic is with that

I checked the FTP sensor and it was reacting to purge control solenoid duty cycle adjustment via scanner. I found out the R-L and L-R terminology in mode 6 stands for Rich to Lean and Lean to Rich switch time. Something about the switch time of 02 wave form which the PCM doesn't like. Or maybe another unrelated enable criteria is preventing it from setting the monitor. I have no DTC's anywhere in the system.

It is a work van and the owner can't afford to leave the vehicle at the shop for us to play with it. He will be bringing it back soon to try to pass emissions. I will post pictures of both newly installed 02 and old 02 wave forms for both banks.

Have you checked Airflow data against what spec says it should be....Eric O had a similar case in this vid. May be worth a watch. I'm sure paul wont mind...

Vehicle came back in today for emissions, they ran it and it got a rejection from testing for insufficient monitors not being set.
Evap monitor has finally set on the car. O2 and HTR are still not ready.
It can pass state emission with at least 1 monitor not being set.

Airflow was showing 5-6 g/s in idle. I compared to a 2015 Express with same 4.8L and it seemed to be about the same.

Last visit I used the Autel to graph out the primary O2's and it looked okay. Today I ended up using the Verus and I did not like the primary wave forms. Now I can see why the mode 6 rich to lean switch time parameter is not happy. It is taking way to long to switch from rich to lean and vice versa. Let me know what you guys think. B1 S1 is the new sensor but seems worse than B2 S1.



Thanks for the video link, I will go over it today.
The second picture is of a known good vehicle 2015 Chevy Express 4.8L

Thank you for posting that video, after watching it I noticed his fuel trims were maxed out. I was a bit disappointed because my fuel trims are showing good. I decided to go ahead and clean the MAF sensor anywa since I have checked every other parameter on the car. It took about 5 mins of driving and the monitors set!!! Who would of thought a dirty MAF was preventing the O2 heater monitor and O2 from being set. Must be a GM thing

Seriously I have to give a big thank you to scannerdanner (Paul) for creating this forum and every member on this great site who contributes to the community. Can't forget Pine hollow, South main auto, New level auto, Triangle Auto and many others for taking their time and creating informative videos online!