I have a 1999 Mazda Protege 1.6L manual. I am experiencing sluggish performance and poor fuel econonmy. My check engine light is on and indicates a touble code of P1141. I do not have access to a list of Mazda codes, but have looked at generic OBD II codes. From what I can ascertain this may indicate a bad 02 sensor, which would I guess cause the PCM to go into an open loop mode and thus give me the symptoms I am experiencing. What I came up with was H02S Bank 1 sensor 2 Heater Circuit Low Input, but this may not actually be the right code for a Mazda. Does anyone know what this code indicates? Any suggestions would be appreciated.

 

Posted to your thread in Gen Tech. Will just past same info here.
You are right. P1141 indicates a fault in the rear O2 sensor heater circuit. The heater is used to help sensors warm up faster so engine can enter closed loop quicker and lower emissions. The rear O2 does not play any role in controling fuel mixture however. It is used only as a way for the engine computer to monitor the front warm up cat converter efficiency. The front O2 is the one that tells the PCM what currect mixture in exhaust is so it can adjust the fuel accordingly. Very unlikely that the code is the source of poor fuel economy and low power. Look instead to the mass air flow sensor on top of the airbox. Has a very high failure rate with problems that you are describing. Have had some luck cleaning these sensors but yours is covered under an extended warranty for 7years or 70,000 miles I think. The extended warranty is available thru Special Service Program #56.