3 O2 Sensors on 1999 Tahoe?

[Tahoepleasue]

I just bought this 1999 5.7 L Tahoe 4 door 4X4. While changing fluids I noticed O2 sensor bank 2 sensor 2 wasn't plugged in. The male plug should be above the t-case. It's nowhere to be found. I followed both wire harnesses that comes from the engine compartment and even disconnected all the plugs and pulled them down to find this O2 sensor plug. I was searching for cut wires in case someone wanted to eliminate that o2 sensor but no cut wires were found. This tahoe is stock, is it possible there are only 3 O2 sensors? What bothers me is that there is an O2 sensor at the B2S2 location just nowhere to plug it in....I have check engine codes p0141 and p0300 if that helps. I searched all day and I know for a fact that there not a plug up there for it.

 

[OR VietVet]

P0141 is Bank 1 Sensor 2 and P0300 is Random misfire. Bank 1 would be the driver's side. Do you notice any misfire at idle or accel or under a load?

 

[Tahoepleasue]

P0141 is Bank 1 Sensor 2 and P0300 is Random misfire. Bank 1 would be the driver's side. Do you notice any misfire at idle or accel or under a load?

Yes, it's missing at idle. It runs smooth under load.

 

[OR VietVet]

Need to pull plugs and see what is happening as far as maybe a fouled plug(s). You may also need to look at the rest of the tune components for age if you did not get any history paperwork with the rig when you bought it. I am assuming you bought it with a CEL on? You need to locate that sensor plug in. Is the unplugged sensor on the driver's side?

You say Bank 2 but that would be the passenger side.

 

[Tahoepleasue]

Need to pull plugs and see what is happening as far as maybe a fouled plug(s). You may also need to look at the rest of the tune components for age if you did not get any history paperwork with the rig when you bought it. I am assuming you bought it with a CEL on? You need to locate that sensor plug in. Is the unplugged sensor on the driver's side?

You say Bank 2 but that would be the passenger side.

I do have the paperwork for the history. New fuel pressure regulator, air intake manifold gasket, egr, plugs, distributor, plug wires, rebuilt tranny, both temp sensors replaced, radiator, radiator hoses, all fluids replaced. The sensor in question is on the passenger side exhaust pipe downstream of the CAT.

 

[OR VietVet]

That's what I am saying. The code is for bank 1 on the driver's side and the one in question is on the passenger side. Besides the plug in being gone or missing the code is for the wrong side. Maybe the wire plugged in to the driver's side is talking about a problem on that side but for some stupid reason there is no code for no wire attached at the passenger side. WTF!

 

[Tahoepleasue]

That's what I am saying. The code is for bank 1 on the driver's side and the one in question is on the passenger side. Besides the plug in being gone or missing the code is for the wrong side. Maybe the wire plugged in to the driver's side is talking about a problem on that side but for some stupid reason there is no code for no wire attached at the passenger side. WTF!

I see what you are saying now, there should be a code for the O2 sensor that's missing the plug....

 

[Tahoepleasue]

I will be testing bank 1 sensor 2 today, if bad I will replace it. If this is the case it should clear both codes. But, that still leaves me with an O2 sensor unplugged. I did find a wire harness company that notes in one of their instruction manuals that these 5.7L vortecs have either 3 or 4 O2 sensors. It's possible that the exhaust system was replaced with a bank 2 sensor 2 input where there was none before the replacement. But if that's the case, why would someone pay for an O2 sensor when they could have welded the O2 input closed. Anyone have the same year and model? Look at your bank 2 sensor 2, is one even there, if it is...follow the pigtail above the t-case/tranny, is it plugged in?

 

[Fless]

But if that's the case, why would someone pay for an O2 sensor when they could have welded the O2 input closed.

Think about it this way: why weld when you can plug the hole with any old sensor, good or bad? Heck, if you think it's a good sensor, swap it with the Bank 1 sensor that's giving the code.

 

[Tahoepleasue]

Think about it this way: why weld when you can plug the hole with any old sensor, good or bad? Heck, if you think it's a good sensor, swap it with the Bank 1 sensor that's giving the code.

Nice, I'm doing that now. I tested the sensor, I'm getting 12 volts to the sensor and the heater circuit is reading 4.1 ohms. The sensor appears to be ok but I will still be swapping the sensors anyway. Also, I noticed when testing the voltage to the plug with the key in the ON position the O2 sensor heated up as did the other 3. So for future diagnosis, instead of pulling the plug to ohm the heater circuit just leave the key in the ON position and touch the sensor to see if it gets warm. I will update everyone....