MG Car Repair: Co emission, air flow meter, digital volt meter

Question
can a bad oxygen sensor cause the engine to run to rich there fore making my car have to much Co?

Answer
Hi Valle,
Yes, it is possible but there has to be an over rich mixture to start with because the 0 2 sensor is just a trimmer to put a final correction on the emissions. It does not have a lot of influence like a temp sensor or air flow meter does.
You can test an 0 2 sensor with a volt meter on the 0 2 wire if it has a heater or on the single wire if it does not by heating the tip with a propane torch while it is out and the volt meter connected. It can also be tested while on the car with a digital volt meter when running. .5 volt is correct mixture and above that is rich mixture and below .5 v is a lean mixture. If you get no reading warmed up then it is dead. If it shows very lean and you suspect it is failing remove the air filter and open the flap in the airflow meter a little and watch for a raise in voltage. .9 to 1 volt is about max possible on the 0 2 sensor.
Howard