I'm sharing my story so that somebody else doesn't have to deal with some of the frustration that I dealt with.

My wife's 2003 Grand Caravan with 3.3l Flex Fuel motor threw a P0135 code the other day. Web searches led me to understand that the problem was related to the heating circuit on the upstream oxygen sensor which is mounted between the engine and firewall on top of the exhaust manifold.

First thing was to test the resistance between the heating element wires, which I believe are the black ones. The O2 sensor plug has a red switch built into it. The red switch must be slid back to release the plug. I slid it a bit too far, and the red slider came out entirely. To release the plug I had to push on the area where the red slider had been. This might not have been necessary if I hadn't removed the red slider.

The black wires showed infinite resistance, so I picked up a Bosch sensor and a 7/8" offset sensor socket from autozone. Well, I got a Bosch box anyway. The sensor says Denso on the side. Go figure.

Even after repeated soakings with penetrating oil, the sensor wasn't coming out. I cut a block of wood to fit against the firewall and support my socket extension so that I could focus all of my attention on the long end of the lever, but even with a long breaker bar, that sucker wasn't coming loose. The action was very springy. I think the offset O2 sensor socket was stretching rather than releasing the sensor.

I got a different sensor socket - this one looked like a deepwell socket with a groove in the side. Still no go. Then I got my 1/2" impact wrench in there...

And the 02 sensor socket rounded off the wrench flats on the sensor.

Argh! The lesson here seems to be: O2 sensor sockets are for *installing* sensors. Removing a stubborn sensor requires commitment: cut the wires and use a proper 22mm 6-point socket.

I was able to pound a 21mm (too small) 12-point socket onto the rounded off sensor, and that guy finally cracked it loose with gentle persuasion from my impact wrench and a running engine (manifold heating up).

The threads on the sensor that came out of there looked terrible, and the new one didn't screw in nicely. Wish I'd had a tap to clean it up, but I just ran the new sensor in there slowly and carefully with lots of anti-seize.

The job was awful, and I learned a critical lesson: O2 sensor sockets suck. They're not up to the task. They'll open up and ruin the part, just like (non tool truck) brake line wrenches.

 

Thank you for the information. You should the one in the early durango's. The right fender well sometimes need to be removed just to get to the upstream sensor. How many four letter words did you use?

 

You don't want to know it now but you may have skipped a step. Run the engine and heat up the exhaust for 5 minutes before you touch it with a socket. It should break loose with ease.

First O2 sensor I changed I was doing the same thing you were doing. Neighbor heard my 50 decible comments and told me to run it and heat it up first. To my delight it broke loose with a nudge. I've read that tip now and then since.

 

Oh man, it was a bad few minutes, let me tell you.

The sensor was in an inconvenient spot, but there was quite a bit of room around it. Enough to get a 1/2" impact wrench anyway.

 

Ultimately, that's how I did it. It's not clear to me how much the heat helped, but the engine was running when that sucker finally unscrewed.