I am having trouble completing the oxygen sensor heater monitor drive cycle

Hello Daniel, good mornin, new replaced part doesn’t mean is good, make sure the ECT sensor never goes below 185F when driving the vehicle once it has reached the normal driving temperature, look for available PCM update, many times a computer flash helps on this type of problem, monitor the fuel tank pressure sensor for appropriate changes during the evap system test and fuel level sensor…

Mario gae you great advice. One other thing I would check is the current measurement of each O2 heater. GM seems to be pretty picky with O2 sensors and we have been seeing a ton of aftermarket sensor issues... even from reputable brands that are OEM suppliers to GM.

Another note... AC Delco does not mean OEM... there are often two sensors available under AC Delco, OEM and an aftermarket.

That vehicle uses a time to activity test for the O2 heater. The O2 current won't directly affect the monitor unless it affects the change in time to activity. The engine uses either Delphi or Denso sensors. Which ones did it have and which ones are in there now? To run the monitor let it sit and cool down, preferably overnight. Simply start it and graph the sensors to see when the heaters turn…

Also important to note that anything that says "Delphi" today has nothing in common with the original Delphi that went bankrupt in the mid-2000's. If you buy stuff from GM that would have said Delphi 15 years ago it will most likely say AC Delco now. (My own truck is a 2002 Chevy, that I have owned since new).

You bring up some good points that a lot of techs and shop owners make regarding parts brands including Delphi. At Delphi we've changed over the past several decades to be sure. Mostly for the good! We are original OE on lots of systems on lots of OEMs - from Ford to Fiat. As a technician (45 years) and veteran technical trainer / hotline adviser (30 years) working under the badges of GM Delco…

You could let it sit for an hour, and then watch the O2 sensor KOEO. All of the sensors should be at 450mv, and all should go to zero at the same rate. When you're in the bi-directional section of your scan tool, you should see how much current each sensor is pulling. If all are about equal, then then one that barely responds is defective. At least you know they're all powered. As Randy said…

Hi Daniel, If you've tried everything else, I wonder if the O2 monitor is temporarily suspended due to an O2 heater monitor issue? When I read your post and looked at the vehicle's model year, I recalled GM's special relearn process being implemented around that time (?) that is performed by your scan tool. A quick google of the acronym I recalled "RCOHT" found a very good O2 sensor article…