Help: CT Emissions failed PO455 & PO 442 cleared then PO 150??
 

CT Emissions first failed my 97 E420 w/ 187K miles with error codes:

PO455 Evaporative Emissions Systems Leak Detected (large leak) and
PO442 Evaporative Emissions System leak Detected (small leak).

I changed the gas cap and reset the codes and ran it for a few days and the CE light came on again so i took it to Autozone to read and they said it gave:

PO150 circuit condition (heated oxygen sensor bank 2 sensor 1)

Explanation: "The powertrain control module uses the oxygen sensor to calculate the air/fuel ratio in the exhaust.

Probable cause:

1 oxygen sensor defective
2. fuel system running very rich or lean check other codes first
3. engine misfire condition- repair
4. fuel pressure very high or low-fuel pump or pressure regulator.

How is it that this new code appears and wasn't in the first reading? Is the oxygen sensor easy to replace DIY? Thanks.

#2 and #3 would possibly be caused by #1, just pointing that out. O2 sensors are usually pretty simple to replace, they can be pretty tight after heating/cooling for so many years and the wires can become brittle.

BTW the car runs fine. I just stopped at CT Emissions and he hook me up just to see the error messages. The oxygen sensors checked out fine! The only error was a repeat of:

PO455 Evaporative Emissions Systems Leak Detected (large leak)

I'm kind of puzzled.

Most likely you have several issues.

Don't try to connect them, they are NOT related.

Have you ever filled the fuel tank while running? if yes, then that can cause P0 455.