We, once again, failed the California smog test. I took it in to a popular local shop that specializes in Mazda repair and so far the bill has gotten pretty large. Now they are telling me that the battery needs replacing as there is a dead cell and it will affect the emission system through the PCM and the car will not pass the smog test unless we replace it.

Does anyone know if an ailing battery can cause a problem with the emission system?

 

A bad battery can cause a failed inspection if an illuminated CEL will cause you to fail in CA. A weak battery can set a code P1795 battery/circuit malfuncion. Can also stored codes for faulty O2 sensor heater when crank voltage drops excessively as this is when the O2 heater check is performed. Code set will one or more of following P0133, P0141, P0155. Otherwise probably not.