I have a 2000 Accord SE with 123k miles. Had O2 sensor replaced 10 months ago, check engine light came on again, claiming same O2 sensor is failed. I understand a service bulletin came out claiming that the ECM (ECU?) had to be replaced as it's erroneously reporting a bad O2 sensor when it's actually okay.

Do I really need to do this if I can live with the check engine light on? Will the O2 sensor (and therefore my gas mileage, etc.) still function properly?

The repair is big $$$, so I'd like to avoid, so long as I'm not harming my car, or wasting fuel. Please advise - thanks!

 

When the CEL is on, the control unit runs in a 'default' mode ignoring certain sensors and using fixed parameters,
Yes fuel economy will suffer.
Service Bulletin 00-046 pertains to 98-02 ULEV and 00-02 SULEV <U>only.</U>
Was the replacement O2 sensor Denso brand?

 

what was the code as I hope it was a heater failure or bad or low signal and not because of the P0420 code..

 

if the repair is replacing the ecu. get a used one. You can get them for around $50. You will have to get the dealer to reprogram the imobilizer.