o2B fuse keeps blowing (about to give up!) Code 0141 and 0161

[est88]

Good evening All, having an issue with my 2001 NBS 4x4 Tahoe. Stock.

So I'm trying to pass smog and was running into a 0161 and 0141 code (downstream sensor heater circuits for both sides). After some investigating, all o2 sensors are good, replaced and verified they work with multimeter. My problem is that the o2B fuse that controls downstream Bank 1 Sensor 2 and Bank 2 Sensor 2, keeps blowing. I have traced all the wires, nothing is burnt, chaffed, etc. All ground contacts look are clean and good to go.

When I use my test light on the fuse connection slots where the fuse plugs in the box, I only get a light for the right side, the left side no light at all. I know this has to be wrong because the o2A fuse next to it gets a light with tester on both sides/pins of the fuse when I prod it.

I have also noticed if I put a new 15amp fuse in the o2B, and turn the key to ignition, wait a few seconds, and start it. It won't blow right off the bat. But if i drive it a few miles and look, it's then blown.

Does anyone have any ideas what could be going on here? Been at it for 5 days and I'm about to give up.

 

[Fless]

With the fuses out of their slots you should have B+ voltage on only one of the conductors in the socket. Are you saying that your O2A socket has B+ on both conductors in the socket with no fuse installed?

Apart from that, are you certain that the upstream and downstream sensors are in their correct positions? Have you tried, one at a time, to swap sensors from side to side to see if the issue follows?

 

[Fless]

One other thing that comes to mind is a sensor that ohms within reason until it heats up, then it draws more current and blows the fuse.

 

[est88]

Actually you are correct, with no fuse installed in the socket, only one side of the socket should show a light with a light tester. Yes i have tested swapping the sensors and the issue follows. I imagine it must be a wiring issue at this point, I'm thinking somewhere close to or possibly at the fuse box. I wonder if possibly the actual fuse socket for o2B could have been damaged either on the conducters or even behind it (if you pull up the fuse box).

I did pull out the fuse box to get a good look and of course everything looks good. I believe there are two pink wires that feed each fuse socket, o2A and o2B. They both appeared to be very secure to the fuse socket and no damage at all since its probably never seen the light of day before, the wires look new.

Open to any additional suggestions.

 

[Fless]

If you swapped sensors and the issue followed the swap, then you have a bad sensor. That is unless I'm misreading what you wrote; if it moved from one circuit to the other when you swapped the sensors.

 

[est88]

If you swapped sensors and the issue followed the swap, then you have a bad sensor. That is unless I'm misreading what you wrote; if it moved from one circuit to the other when you swapped the sensors.

Well the fuse controls both downstreams at once. So when i swap the o2 sensors it doesn't change anything. It still blows the fuse. I am not getting a code thrown yet, I might have to drive enough for the drive-cycle to hit. But what I am noticing is that on my OBDII scanner, my HTR-RDY, EVAP-RDY and CAT-RDY are all still showing "INC" instead of "OK" or ready-to-go. "HTR" is the o2 sensor heater i think and I think EVAP and CAT might be related? I'm not 100% sure.

I believe those must all be "OK" in order to pass smog

 

[Doubeleive]

Well the fuse controls both downstreams at once. So when i swap the o2 sensors it doesn't change anything. It still blows the fuse. I am not getting a code thrown yet, I might have to drive enough for the drive-cycle to hit. But what I am noticing is that on my OBDII scanner, my HTR-RDY, EVAP-RDY and CAT-RDY are all still showing "INC" instead of "OK" or ready-to-go. "HTR" is the o2 sensor heater i think and I think EVAP and CAT might be related? I'm not 100% sure.

I believe those must all be "OK" in order to pass smog

ok so do this
unplug one downstream sensor and see if the fuse still blows, if it does then plug that sensor back in and unplug the other sensor and try again
if it does not blow with one of the sensors unplugged then you found your culprit.
if it still blows no matter which sensor you unplug then you likely have a wiring short, that you should be able to trace with a ohm test on the harness
***edit be sure to verify the issue, if it does not blow with the 1st downstream unplugged, then plug it back in and unplugg the other one and verify

 

[est88]

ok so do this
unplug one downstream sensor and see if the fuse still blows, if it does then plug that sensor back in and unplug the other sensor and try again
if it does not blow with one of the sensors unplugged then you found your culprit.
if it still blows no matter which sensor you unplug then you likely have a wiring short, that you should be able to trace with a ohm test on the harness
***edit be sure to verify the issue, if it does not blow with the 1st downstream unplugged, then plug it back in and unplugg the other one and verify

It blows even with both unplugged. Can you explain how I can perform the OHM test to find the wiring short? I've traced it as best as i can from the downstreams wiring thru the underbody and up the passengers side wheel well and up and around the back of the engine, and then to the fuse box. Everything looked good from what i can see, most of the plastic wiring covering is still intact and i couldn't find any visible shorts. Although i didn't crack the plastic to look in, i figured if the plastic is there it's gotta be good, no?

i kind of feel the short might be in the actual fuse box, because sometimes when i pull up the fuse box to examine the wiring/connectors, i can sometime get the fuse to not short/blow. And then if i move the fuse box a little, it'll blow.

 

[Doubeleive]

sounds like you probably found the issue then if you remove the fuse box look under neath where the fuse goes if anything is burnt or melted that would be the source

 

[est88]

Thats the thing though nothing is burnt or anything? It all looks perfect.

Get this, messed with the fuse box a little. Then I unplugged both rear sensors. Went and put the fuse in. Didn't blow. Started car didn't blow. Then plugged in o2 rears and didn't blow yet. Driving it and now o2 HTR-RDY is OK no longer inc. No idea if its gonna blow again once I turn car off.