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I had the CE light on since I bought this car a few months ago. Reading the codes, I found and fixed a RS relay problem. This was described here:
http://www.brickboard.com/RWD/volvo/1280709/740/760/780/obd_codes_now_see_dont_possible_bad_rsr_regina_221_122_321_radio_suppression_relay.html
The 2-2-1 code remained, and according to the FAQ it means a bad oxygen sensor on a Regina. The sensor I had in place looked OK externally, but measuring the voltage gave me very low values. This was described here:
http://www.brickboard.com/RWD/volvo/1271058/740/760/780/regina_oxygen_sensor_testing_221.html
I found a fairly inexpensive sensor on eBay. I made sure it was the correct NGK one. Yesterday I finally got around to installing it. Here's my takeaway from it:
Replacing the oxy sensor looks really easy. My sensor looked fine externally. Looks can be deceiving and were in both cases.
The sensor connectors can be a royal pain to unplug. For some reason this was easier the first time I did it. The best way to disconnect the single wire connector is to carefully slide the rubber boot off and up the wire baring the spade connector. Then you can grab it and not the wire.
The wire is held on by two clips on the frame. Both are on the underside - nothing holds it to the firewall.
Once the wires are loose, it is time to unscrew the sensor. This is where the fun starts. Mind you, my downpipe is not rusty, it has been replaced relatively recently. Regular wrench/socket do nothing. A breaker bar is really hard to use on a car that is on ramps and not on a lift and equally useless. The only thing I succeeded in doing was getting the sensor socket (that's a deep 7/8 inch socket with a cut in the side for the wires) to slip around the sensor because the cut allowed it to spread.
Next, I tried the air impact wrench. Lots of noise to no effect whatsoever. This meant it was time for the heavy artillery in the form of a gas welding rig. I really like the welding torch for heating stubborn fasteners - it allows to concentrate heat in a small area quickly. What takes 10 minutes with propane takes 1.5 minutes with oxyacetylene.
Heating the bung made it expand - I heard the crackling - and the sensor got loose.
As an aside - grabbing a socket you just used to unbolt something you heated up is not a god idea. It can be hard to find after you toss it, and people within earshot may learn new words they don't necessarily need to know.
Looking at the sensor in daylight I noticed a curious thing. It corroded at the juncture of the thin cylindrical portion and the hexagonal portion. I couldn't see that under the car. I'm thinking this might be the cause of failure.
The installation was straightforward. The new sensor fit a bit tight, even with threads coated with antiseize.
I have driven from Minneapolis to Eau Claire, WI and back immediately after. No codes have been set. The light remains off, and my idle got noticeably smoother.
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