C220 Oxygen sensor question
 

Question about a '94 C220 (120K miles) Oxygen sensor...recently I got a "check engine" light and read the code using an SnapOn OBDII reader...the code returned was P0141 "O2 Heater Ckt Bank #1 Sensor #2". The light turns on infrequently, but it's usually on a very cold day and immediately after I turn the ignition switch on. So I'm assuming it's just a bad oxygen sensor heater.

I understand the C220 has two oxygen sensors...one at the exhaust manifold and the other after the catalytic converter. Which one is Sensor #2? (I get conflicting responses on this) or how can I figure out which one it is...disconnecting one of them and trying to get a OBDII code isn't working.

Second question is...are both oxygen sensors the same (connector wise/part number wise) or should I make a diagnosis and then order the appropriate part number?

Thanks,
Chandra