DIY Changing the Yukon Tahoe Driver Side Pre-Cat Oxygen O2 Sensor After OBD P0135

So the ‘Service Engine Soon’ light went on for the first time in the Yukon Denali. The truck runs great with about 100k miles so I figured it was something easy like an O2 sensor. I didn’t want to spend $100 at the shop to find out what was wrong so I bought an Equus 3030 OBD-II reader. It should pay itself off after the first use.

Sure enough I got the code P0135, bad O2 sensor, pre-cat, drivers side. I’ve replaced those on the BMW so I figured I could change them on the Yukon. I went to O’Reilly and they wanted $100 for a replacement. Holy Toledo! I don’t even want to ask the dealer what they want. Luckily, Amazon had it for about $50.

Installing it was mechanically easy, but a tight fit. This one O2 sensor is right between the exhaust pipe and drive shaft so you need skinny arms to actually disconnect/connect the sensor.
I assembled my huge torque wrench and O2 sensor socket, the only tools required to complete the job.


So after safely lifting the car, (I used my home made LONG 2×10 board lift for my BMW (long to clear the low slung front air dam on the car)) you’ll find the sensor that looks like this:

Here’s the sensor in relation to the exhaust pipe and drive shaft:

…that’s where you need to squeeze your arm. I’m average build and while I could reach the connector, I couldn’t manipulate it.
Disconnecting the thing is tricky. GMC went with the belt and suspenders method by not only having a mechanical lock on the connector, but also a blue keeper. I had to squeeze some scissors up there to break the keeper, then the Mrs. manipulated the lock and disconnected the sensor.
Plugging in the new one is also tricky given the space constraints given the new gasket around the connector. After the Mrs. tried for five minutes, I threaded some channel locks up there to squeeze at the two marked spots on this image:

I torqued the new sensor to 31 lbs/ft and was done.
Mechanically this is a 1 or 2 on the difficultly scale of 1-10, but given you must lift the truck and have skinny arms, I’d give it a 4 on the difficulty scale.