Hello Gurus of Rennlist

So far after the last meltdown incident all seems to be well. The car runs cool, the tank doesn't leak, no intermix, and generally all seems well after about 250 miles. I replaced water pump, thermostat, flushed, and put in new unicorn tears.

But, (always a catch) I am getting a P0139 fault code. From what I have learned from my research, this is the O2 sensor behind the cat on the passenger side. This would make sense as this sensor was doused by the overflow hose on numerous occasions.

I just want to confirm that this is the correct diagnosis and it looks like a pretty simple fix, if it is.

Thanks!

 

My reference:

P0139 - Aging of O2 sensor behind the 3-way converter (cyls 1-3).

There's not much if anything you can do to an O2 sensor in way of resurrecting it. About all you have available to you is to ensure the connection is good. It might be worth the effort to carefully disconnect the sensor from the wiring harness verify there is no moisture present. Do not use any cleaner at the connector just let the moisture dry. Then connect the sensor back to the harness and make sure the connection is sound and see if this helps.

Frankly if you found any signs of moisture my recommendation would be to just replace the sensor. But I'd be sure the engine harness connector was dry before connecting the new sensor to it.

Really I think replacement is called for of at least the indicated sensor and possibly sensors on both banks.

Unless the two sensors are relatively new I'd replace both sensors. The sensors age and what you would have is a new sensor and an old(er) sensor on the two separate banks and the two banks could end up with dissimilar fueling due to the differences in sensor performance.

 

Thanks Macster. I found the Bosch ones on Amazon for under $100!
I'll do an inspection and swap before I replace them first.
I would imagine the deluge of water from the overflow didn't help matters much.
But if I suffered only a bleeder valve and 02 sensors, I'm not going to complain.
This car has been very good to me!

 

My experience is the sensors are relatively immune to being affected by exposure to the elements. They live in a pretty lousy location compared to other cars with front mounted engines but appear to be well suited to this location.

My Boxster experienced a failed coolant tank which gushed hot coolant down and almost certainly doused at least one O2 sensor on the passenger side of the engine. Previously to the coolant tank failing, some years back, I had driven the car a short distance -- under a railroad overpass -- through deep standing water -- water up to the door sills -- and I'm sure all 4 sensors got pretty wet. Later that day I ended up on a street with curb deep standing water -- there has been a series of heavy rain storms moving through the area and areas of the town were prone to local flooding -- and drove at a slow pace -- barely above walking speed -- through the water for a couple of blocks. After all of the above the sensors were unaffected.

However, the sensors have been replaced a couple of times over the years. What appears to do them in is just miles. They eventually wear out or in the case of one sensor in my Turbo just fail (at 132K miles) with a bad heater circuit. (This failure is really just due to age, wear and tear.)

Regardless you are certainly free to replace one or both as you see fit.

Handle the sensors with care. Do not touch the tips. Do not attempt to measure any resistance of the new sensors. Do not use any thread lube. Be sure the electrical connection to the wiring harness connector is good. With my Boxster the connnectors have some kind of latch that when the two connectors are fully connected the latch catches and hold the two connectors together so vibration can't cause the connector to work loose over time.

 

The Bosch O2 sensors come with high temp anti seize preapplied. Makes it a ton easier to get them out when you want to replace them.