Just thought i would post this hope it helps someone in the future.
I just bought a 940 Wagon 1993 4 cylinder. Only paid $200 for a roadworthy car and it included 3/4 tank of gas, 242,000 km. The check engine light was on and the owner had spent a small fortune with mechanics trying to work it out. He gave up on the car and i bought it. Once i got home i read the code took out the o2 sensor and cleaned it and the wiring in the engine bay. No change so i pulled out the lambda fuse and put it back in perfect no more light gone. Must of been a dirty fuse contact tripping it. The symptom i had was if i cleared the code and started the car cold check engine light would be off and would turn on once it got to the stage the thermostat opened.

Good work!

The poor contact on the oxygen sensor heater fuse is a common cause of a 212 in an 89 or later 240, where the fuses are less secure in their holders and the circuit is shared by a tank pump.

Recent example here: http://forums.turbobricks.com/showthread.php?t=348596
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Art Benstein near Baltimore

"The headlamp restorers rely on temporarily filling microcrevices resulting from paraficial wind abrasion and UV brittling."

Thanks for your post! I will be cleaning my 240s fuses/fuse box contacts and if that doesn't fix it, the 02 sensor, before spending $100 (US) on the purchase of a new one.

Congratulations on your purchase!

Excellent diagnosis. That would all make sense as the O2 sensor input is ignored for the first couple minutes that the car is started up cold. Once it hit operating temp, the ECU would then look for the O2 reading which was way out of range due to the corroded fuse.

Sounds like $200 well spent.