My advice is to go with FCP's direct fit for $132. The so-called "universal" for $49.95 is basically the same Bosch Universal you just tried, with maybe different length leads. It WILL NOT WORK in your car, believe me. I haven't been able to convice Nick that his "250-2300 Universal 3 Wire Oxygen Sensor will fit all 85-92 models, $49.95, Walker" listing is mis-leading—but I'm convinced that it is.

Here's all I know about the Titania sensor, and the search for a cheaper version. IMO, the titania has a longer life, which makes it worth more—and trying save a few bucks on a 100,000+ item by splicing leads, and thus possibly reducing reliability, is false economy. My original is fine at 140,000 and will get a direct fit replacement when the time comes.

This is a summary of what I've found on the Regina O2 sensor (Titania type) so far.
Key points:
• It's a good sensor (see "Advantages" below)
• NTK (possibly the sole producer) may have licensed NGK and/or Walker
• Most promising Direct Fit numbers are Walker 250-23811 and NTK OTA4F-B, or FCP's Volvo #3517394 (a Walker brand)

Titania Sensor Advantages:
Compared to the more common zirconia O2 sensors, titania sensors have three advantages: (1) they don't need an air reference (there is no internal venting to the outside atmosphere to plug up); (2) they have a fast warm-up time (about 15 seconds); and (3) they work at lower exhaust temperatures (they won't cool off at idle and they can be located further downstream from the engine or used with turbochargers).
-----------------------------
From Web search March 4, 2004 -- Polish Parts house, Scandicar.

Titanium Oxygen Sensor, Three Wired
Wire Colours:
Black Connection: Signal out
Red Heat + (positive)
White Heat - (negative) and Signal feed
Check the colour of the wires, a Red wire means a Titania Oxygen Sensor.
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posted by  lucid   on  Fri Feb 27 10:21 EST 2004 )
>>Extract from a 2/27 04 post<<
(NGK 25002?)
..."NGK does list a Titania sensor for a 940 na, with a "suggested" list of $236 (P/N 25002), but I couldn't find it on the clubplug.net site. So the FCP price of $140 or so may be as good as it gets."<<
(This 25002 may turn up elsewhere, but I question it.)
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posted by  tomtbone   on  Thu Apr 15 13:39 EST 2004
(Walker 250-23811?)
Well I did find out little information today by looking in the walker online catalog. The part number that FCP lists is actually not for ALL models according to the Walker catalog. Walker lists another one for the regina models, which is evidence that FCP is wrong.. . .here is what the Walker catalog says:

1992-89 2.3 L w/ Regina Engine Control System
Direct Fit # 250-23811 Universal # 250-23881
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>>>online research Apr 27, 2004<<<
The Bendix/Siemens fuel sytem models use a different type sensor and it is not interchangeable with the Bosch units.
This sensor does not work with a .5 V reference out of the ECM as does the Bosch versions. This type uses the heater power supply to feed a sensor circuit (that) responds to O2 level variations. The Bosch type employs an electrochemical reaction and the heater is for stability of the temp (and therefore the signal) and not for the supply of current to be modified and used as output signal.
SOURCE:
http://216.239.41.104/search?q=cache:4t_ja5f8dCIJ:www.volvoclub.org.uk/faq/EngineSensors.html+volvo+bendix+regina&hl=en-----this is the URL
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posted by  ringlee   on  Sat Apr 24 21:45 EST 2004
(NTK OTA4F-B?)
Per the pocket data booklet, Regina cars through 1993 use a Volvo -394 sensor which is the same as NGK OTA4F-B. Tracing that should give you some info.
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posted by  Sumerduckman   on  Sat Apr 24 07:48 EST 2004
(Walker 250-23811?)
Yep, Walker# 250-23881 universal, Walker direct fit 250-23811. They got 'em at www.oxygensensors.com for $95 and $125. Also NTK # 25002, do not have a price.
All of the Regina systems require the correct Titania sensor( they use resistance changes to a feed signal from the ECM, not voltage generation) to function correctly.
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posted by  tomtbone   on  Tue May 4 21:54 EST 2004
(NTK 25002?)
Hey guys/gals. I installed my new NTK 25002 sensor today. I was the one with the 740 that the PO previously spliced in a Bosch. Well I can tell immediately that the idle is smoother and the car seems to run better as well.
(Lucid Note: I believe he later found that the 25002 was wrong, but can't confirm it now 10/24/04)
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posted by  tomtbone   on  Sun Oct 3 19:41 EST 2004
(NTK 25063?)
I did a lot of research on this myself, talked to a lot of guys even the people of NGK. I have a 91 Rex system 740
Best place is to just order it from NGK's website at www.sparkplugs.com. ITs $120 there. Don't get a universal one because it will not have the titania construction most likely and you will have to splice in the wires as well. I believe it is model 25063. Feel free to email them on their site though they email right back sometimes within the minute!
----------- END OF SUMMARY, 10/24/2004-----------

--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.