New front O2 sensor, 2000 V70 NA

[RayF]

Persistent code said bad front O2 sensor and it's safety inspection time, no engine codes allowed. So I decided to do this.

I went absolutely el-cheapo way with a universal 4 wire sensor from eBay, $10 plus state tax, free shipping. They responded that it shipped almost immediately, same day, late Thursday 6/15. Predicted Tues arrival but it came yesterday, Saturday, 6/17, way faster than I figured. USPS delivered for me, Yay.

No rain today so I did the job. All from above, leaning in or flat on my chest atop the engine looking straight down at it. With an LED headlamp on. Gently twisted off at each end the cardboard-and-foil preheater tube above the exhaust manifold, for cleaner access, and set it aside.

Worst part was unplugging the old sensor. I needed the plug so had to do it clean.

I found a good picture of the plugs on a parts-sellling website, think big bird with a big beak that sits on pilings by the water. But not much description of how to release the clip and work the plugs apart.

Originally the receiving sockets for the plugs are mounted on a steel bracket by nylon attachments, but those were long gone and sockets and plugs were just floating in the air, nothing to pull against. Needing one hand to hold the socket part, another to pull the plug, and a THIRD to release the latching tongue, I was SOL.

I guess there's a way to trip that latch by pressing straight down with a small screwdriver but I couldn't find or feel the place to do it. And no free hand to hold it anyway. But bringing the flat blade of a toy-size screwdriver (pocket-clip variety) straight in from the cat side into the rectangular mouth on the top side of the plug, you can feel the plastic latching tongue and slide the screwdriver blade above it and leave it there holding things unlatched. Then on to holding the socket part and getting the plug to come loose.

It's a snug fit, no wobble or play, made worse by years of road dust filling any crevices and locking things up. And there's no place to pry, either on the socket or the slick sides of the plug. I took my trusty pair of 7" curved-jaw Vise-Grips, loosened them quite a bit, and set them very loose but just gripping the tail end of the plug near where the wires come out. There's kind of a bump there that keeps them from sliding off. Pushing against the vise grips, holding socket part tight, tiny screwdriver keeping latch tongue free, the plug popped free.

I had just replaced the cat itself and used never-seize on the O2 sensors. So I was able to get the flats of a 7/8" wrench on the sensor from above and get it loose, then finger-spin it out.

The new sensor came with four crimp connectors and a helpful little printout showing the colors of various brands of sensors so you can match theirs up. The two white wires from my OEM Denso's plug went to two blacks on theirs, the black to a blue, and the grey to a white, if I recall. Cut the old sensor off the Denso plug, near to sensor, cut back the insulating sleeve a little, and strip the four wires, and the four wires on the new sensor, about 1/4" each. I also had a piece of big heat-shrink tubing I slid on to use at end to keep the four crimp connectors in a neatish bundle.

Advice, crimp all four connectors onto the PLUG wires first. Denso uses very fine-stranded wire, and it's not easy, even smoothing and twisting the strands together, to get all the strands into the connector ready to be crimped. The aftermarket universal sensor came with coarser stranded wire that kept together easier when poking the wires into the crimp connectors. Both, by the way, are stainless steel wire. There's no soldering that, only crimping will work. I then slid up and heat-shrank over everything the tubing I had slid on ahead of time.

I also cleaned any dust off the plug, rubbed it with a little candle wax, and modded it a little bit, in case I ever have to take it apart again: I used a 1/4" bit to start just the beginnings of holes, three little pits, one on each side and one on the bottom of the plug, to poke a screwdriver in to help pry it apart. And I used a tiny file to remove the latching point, up inside the rectangle at top. No way in hell that part is ever going to loosen once fully plugged in.

Headlamp on, flopped on belly atop motor, all back together, with good luck flipping the 7/8" wrench back and forth to get it nice and tight. Cardboard-and-foil hot air tube back on, from air cleaner box to tin atop exhaust manifold.

Used my code reader to clear codes, started the car, and ALL IS GOOD! Sticker time tomorrow!

[abscate]

You will need to drive that 50-200 miles to get the OXS and CAT monitors ready before inspection.