O2 sensor

Check engine light came on yesterday and has been on for a few short trips now on my 2001 GMC Sierra 1500 4.8 V8. Took it by Auto Zone today and they said it was code P0161 or a bad O2 sensor--bank 2, sensor 2. Which he said is the passenger side after the cat. I found some test instructions on it today and found in the wiring harness pin D is receiving 12 volts and pin C is grounded as they should be. On the O2 sensor side of the connection I measured the ohms across these pins and got 4.2 ohms. I'm told it should be between 5 and 16. Still I expected it to be either ok or an open circuit. Does 4.2 vs between 5 and 16 sound like the problem? Or as I write this do you think he got the location of the sensor wrong and I tested the wrong sensor? After all I hear bank 1 is the side with cylinder 1 and I don't know if that Drivers or Passenger side. Too cold to go check the other side right now.

Had bank 2 sensor 2 code on my 04 Silverado. Passenger side, sensor on rear of converter. Mine was easy to change. I cleared the codes after I replaced the sensor. Be sure and put some antisieze on threads of new sensor.

Bank one is the driver's side on that so I think you're working on the correct sensor. If that code is for heater performance I think you're going to need a new sensor.

First of all, if it is CCCCOLD where you are, I would clear the code and see if it returns

On your truck, bank 2 is RH/passenger"s side.

The front sensors provide feedback for the fuel control system.

The "2" sensors (Bank 1 sensor 2 and Bank 2 sensor 2), behind the "cats" report cat efficiency to the emissions warning system and DON"T/CAN"T control the fuel, so if there is NO code for the front sensor, it is strictly an EMISSIONS problem, NOT an engine or fuel system problem

Your PO161 code specifically points to the HEATER circuit that warms the sensor so the system can go closed loop.

I would ASSUME the computer keeps tack of the time, after startup, how long it takes the sensor to "come on line" (heat up and produce a signal), and if that takes too long or does not occur at all the code will be set.

Condensed moisture in the exhaust system, or snow and ice caked under the vehicle can cause this,m as well as a failed sensor or a problem in the heater supply circuit.

So, it"s NOT an emergency-engine"s-gonna-die situation, and I would clear it and not get too excited about it "til warmer weather and IF it re-occurs.

If you are NOT subject to emissions testing in your state, considering the vehicle is 13 years old and you MAY not want to start throwing a lot of $$$ at it, you can have someone with a "tuner" program (such as HP Tuners) simply tell the "puter to IGNORE the rear O2 sensors.

End of issue.

"put some antisieze on threads of new sensor"

Yes, but VERY LITTLE, and keep it off of the first thread or two as it will contaminate/ruin the $$$ sensor if it gets into the sensing element.

Chris, It is the post O2 on the right side. They have a problem with the wires rubbing and intermittently shorting out on the frame. Replace the O2 sensor and add something to protect the wires as they go over the frame. Use a piece of hose or wrap with tape. David

Thanks for the in depth answer. I have almost a year before I have to get it inspected again--yes, it has to pass emissions. So, I'm just going to wait until then and see what happens.

I had a 95 gmc serria 6 cylinder gave me an o2 code. Come to find out a mechanic left off a hose when he replace the dist & rotor

My 01 Silverado 4.8 had cold weather check engine light for years. Turned out to be vacuum leaks under the intake. The dealer had the heads off under warranty, looked like the reused the gaskets.

Any "unmetered" air, as in air that didn't pass by the MAF sensor will cause the mixture to lean beyond the ability of the O2 sensor to read, and will set the 161 code. The problem is intensified by cold dense air requiring more fuel to meet the proper a/f ratio.

Check for vacuum leaks, crankcase air leaks, plenum leaks... The light will clear itself once the mixture gets back in range.

His issue/trouble code relates to a O2 sensor heater issue. Your leaky intake gaskets (although common) are another issue and trouble code, entirely.

Bob,

You seem pretty knowledgeable with these systems. Do you know of a way to eliminate the heater code with a wiring change or running a resistor in-line with this circuit? I don't have access to a programmer that can eliminate this. And I don't want to spend a bunch of cash on a junk code that doesn't effect anything.

I have already installed the dual plug anti-fouler adapters to pull the sensor out of the exhaust stream. This worked for me on another truck that I had to pull the cat off because it plugged. Thought I would try it on this one. No luck though. It is just the annoyance of the "check engine" light that drives me nutz. And if we ever go to selling it, codes drive many people away.

Thanks!!

The computer looks for a varying voltage from the sensor, within a certain range, so a simple resistor will not "trick" it for very long.

I know a few years back there were some gadgets on the market that mimicked a working rear O2 sensor. Don't know if they worked, or not.

If vehicle age/emissions testing where you are allows it, editing out the 'puter's "looking" at the sensors ends the check engine light, once and for all.