So I had the job done, bought 2 new Eastern Catalytic direct fit converters, had them installed. Night and day difference---no more rattling, feel a little more power, etc. So that solved my Cat problem.

But, after a few days of driving the P0036 (And related P0054 and P0141) codes came back for that pesky Bank 1, Sensor 2 heater circut. I had them put brand new O2 sensors (Bosch Premium) all around, pre and post converter, so I know its for sure not the O2 sensor (I've been through 3 downstream sensors now).

Wondering what the hell else this could be. I had my mechanic, and then even the GM dealer, do electrical testing and they inspected the fuse block for corrosion, ok. Performed Load Test on harness, ok. Inspected harness for chaffing or shorting to ground, unable to find defect. Their ultimate reccomendation (of course) was a gM O2 Sensor that was $225! Clearly thats not the issue, as Bank 2 Sensor 2 doesn't get the same code after swapping O2's, and as I said I've been through 3 sensors.

My mechanic did testing before that and wiring found to be ok from ECM to O2. Wiring found to be ok from fuse to O2 sensor. Good power when key on. ECM pulses ground to O2 when key turned on. O2 heater resistance at 7-8 ohms, relatively normal. Everything working as required at this time. They thought maybe faulty O2 sensor (not that now) or ECM could be potential cause.

Anyone have any other ideas for what this could be? My next thought is to maybe just try a new harness....but I'm lost for words here....

 

Did you come up with a fix for your issue?

 

Nope, no fix yet. The other day, I tried just changing the fuse for the heck of it, and cleared the code. A few hours later, 9 new codes came back (ALL o2 sensor codes possible), so I went back to the new fuse and it had blown---telling me something electrical is up. I went out and bought more 15A blue fuses, put a new one in, cleared the code, and for the past 2 days (probably 15-20 starts), no codes have come back up yet. I read that it takes 3 consecutive fails for it to trigger those o2 heater resistance codes, so all good so far. I'm anticipating that it will come back, but maybe I get lucky and it doesn't? Will update here as soon as I have more news.

 

Yup, spoke too soon. CEL came back on tonight. Same 3 codes all related to O2 Heater Resistance on Bank 1 Sensor 2 (P0035, P0054, P0141), but now am also getting a P0060 code for the Bank 2, Sensor 2 sensor.

I saw someone else post somewhere that the lousy stock battery terminals might cause some weird electrical issues. I ordered 2x Stinger SPT53501 Battery Terminals, will have those installed next week as a first step. But other than that, the only "answers" I've been given are: change the ECM (from my mechanic---estimated $750ish), or use GM O2 sensors (from the GM dealer---estimate $675---crazy). I know it can't be the O2's because my original AC delco's on there threw the same code at the start. They still work so I can have the GM guys pop them back in to see that its something else....even though all the electrical testing checks out. The blown fuse yesterday that I found tells me also that its something else. The fuse I've put in since hasn't blown.

Hate these electrical issues. The only issues I've had with my H3 Alpha ever have been weird electrical issues/ Emission related engine codes that are electrical in nature. I baby and maintain the thing tooo...fun ride otherwise. On the bright side, driveability doesn't seem to be affected during all this at all....just I hate looking at that stupid orange CEL light! Huge pain!

 

Yup, going through the exact same things after I changed my cats to the MagnaFlo cats since the old ones were bad.
Let me know if you ever do come up with a fix and I'll do the same.
Thanks

 

Will do. What's weird is I had these issues BEFORE changing my cats, and specifically bought the direct fit (Eastern Catalytic GM) to avoid any after-market or universal cat issues.

Have had the P0036 with my original AC delco sensor, with Bosch, and NTK replacements. Downstream only.

At a loss here

 

Just throwing this out there since it seemed to solve my issue. I was getting the P0300 and P0301 codes early this year. I went through all the steps trying to resolve the issue, new coils, cam sensor, O2 sensors, new battery terminals, cleaned MAF, cleaned throttle body, new air filter, new plugs but no luck. The last piece I did were the battery terminals but the code would still pop up after letting truck idle a few minutes or if I turned the truck off and back on within a few seconds. At this point I threw in the towel and just tried to ignore it but then another issue popped up. Randomly the truck would lose all electrical power while driving and come back on within a second. When this happened the second time I checked the battery terminals and cables and decided to make sure everything was getting a good connection. All looked good at the battery terminal so I went to the fuse box where the cables connect. I removed the positive and negative cables there, cleaned the connections on the cables and also the main fuse, with sand paper until it was all nice and shiny. Put it all back together and to my surprise I never saw the codes again. Been over 6 months with no issues. Maybe give it a try, you never know, good luck.

 

I have posted that the FIRST mod to do to every H3 & H3T is to replace the crappy azzed POS OEM battery Terminals with a quality aftermarket set, like Stingers or your favorite brand...... probably near 100 times. If you google "H3 Hummer Battery Terminals" one of the first images to come up is my truck battery with Stingers installed. I was not kidding. Every one of them will fail. Only a matter of time.

Always do the easy stuff first, before you waste time to chase down electrical Gremlins. It may not turn out to be your problem, but it is a necessary mod none the less.