P0141 What to replace first, Catalytic Converter or the Sensor?

[DynoXG]

It's a 94 C220, 204k miles. Just got a CEL with P0141. I erased it and it came back the next day.

P0141 O2 SENSOR HEATER MALFUNCTION (BANK1 SENDOR 2)

I know this is the sensor after the cat. Which is most likely to go bad, the sensor or the Cat?

[stox]

AFAIK, heater failure is always the sensor.

[DynoXG]

Thanks stox. I thought it might be the cat because of the high mileage, but your post gave me great relief. Thanks.

[NISMOPOWERED]

i think the rear sensor heater is relay controled so i would ohm it and see what you get. if you get under the car and unplug. look on the sensor plug and find the 2 wires that are the same color. you should find a black sensor wire, a white groung wire and 2 greys for the heater. but the colors are sometimes off but the heater wires will be the same color. if it ohms ok then turn on the car and se if you get 12 volts from those two wires. use an ohm meter not light and you will have to try both ways as i am not sure the wire code on the car as to ground and hot.

[DynoXG]

That's a great tip. I'll do this test. Any idea what ohm reading I should get?

[NISMOPOWERED]

well if you get 12 volts at the car harness with the o2 disconnected them 90% its the sensor. basically if its getting power but has a code then its bad. that should make it easy.