from the lh 2.4 wsm dated 3/93

code 212-o2 sensor signal absent or faulty.
testing-engine is warm, use meter on o2 connector and look for 0.1-0.9v.
to check voltage supply to o2, disconnect 02 connector, check for .5v on lead from ecu.

from the regina/rex wsm dated 9/91

code 221-os sensor signal absent or faulty.
testing-engine is warm, use meter on o2 connector and look for 0.1-1.2v.
disconnect o2 connector, check for 1.2v on lead from ecu, after a while.
to check voltage supply to o2, uplug heater connector and look for 12v on pin 2.

so the lh gets it's voltage from the ecu at .5v and the bendix get it's voltage from the heater circuit and it's 12v. good enough for ya? and so it goes, chuck.