Engine code PO 161

[72 5500]

Got a reoccurring code 161 on my 97 K1500. Heater circuit not working on O2 sensor right bank after the cat. Replace the sensor and the light stayed off for a few weeks and now it's back on. Cleared the code and back on after a few days. Has battery voltage at the plug and ground. Checked the heater side on the sensor and it was within specs. 5.2 ohms. Where to go next???

[storm9c1]

Sounds like an intermittent problem. Have you carefully traced the wire past the connector? Somewhere above the connector, it could be damaged. Mice like to chew these or they get frayed by rubbing on something, etc. So trace it as far as you can. Look for damaged insulation or pinched spots.

What brand sensor did you use? Let me guess... Bosch? If this only happens on really cold days, it could also be caused by a crappy heater in the new sensor. The only way to solve this is to buy a better brand sensor. But I would check the wiring and the connectors first.

Years ago I had something similar happen. I had an older analog volt meter laying around. So I taped it to the dash and and ran 2 wires out the door and down to the heater wires on the sensor. Turned out that every once in a while, I'd see the needle jump (this is why a digital meter wouldn't work, it had to be analog to see the jumping). I dug around the wiring harness and never could find the break. I suspect the insulation got damaged by a mouse or something and eventually salt got in it (thanks PennDOT) and corroded the wire internally somewhere. I ended up running a new set of wires directly from the PCM to the O2 connector. Problem solved, but this is a more extreme example.

[72 5500]

Yes it was a Bosch, I had to look back and see what they sold me. Did not check the wiring yet, but I will do that. Have to get it through the state emissions test in April.

Thanks

[68c10airstream]

It's getting late but i'll throw my 2 cents in. From memory the pcm controls the ground side of the heater, 12volts + comes from the fuse box. I'll relate this scenario to a light bulb circuit to help out. As an example say you put 12v+ to one side of the bulb and then complete the circuit on the ground side (the pcm is doing this). If you remove the ground, and now check the wire coming from the bulb right before the pcm 12v+ would be present and available to be put to ground.

So the pcm is looking for the 12v+ to be avaliable going from the fuse through the heater and up to the pcm before it takes it and switches it to ground, and the pcm also monitors how much amperage is on-line to know if it's healthy.

If you go to the pcm and figure what wire the pcm is switching to ground and monitor it with a dvom you should be able to tell what is going on. I suspect poor connections somewhere, especially underneath the vehicle.

I take old parts and remove the terminals and save them to use for what i call "terminal drag tests". Use your old 02 sensor terminal to drag in and out of it's matching terminal and you should feel slight drag! I have fixed many,many vehicles for drivability, check engine light issues from spread apart terminals. I cringe when somebody says they have checked every terminal and they all look good. You can probably guess what my first question will be! Enough of my rant, good luck.

[72 5500]

Thanks for the input, it is greatly appreciated.

[storm9c1]

Agreed on the connector. Silicone grease also helps keep out nasty stuff. But if the connectors are already corroded or don't fit tight, it's an uphill battle.

I've always had bad luck with Bosch O2 sensors on mid/late-90s GM vehicles. Not saying that's your problem for sure. I just won't install them on mine. Denso O2 sensors are a cheaper alternative that seems to work better than Bosch in most cases (NAPA). And of course A/C Delco or Delphi is the best bet if you want it one and done. For the downstream O2s, it usually doesn't matter as much though, which is why I'm wondering about a wire or connector issue.