Hi guys, quick question here for those of you knowledgeable about the control scheme of the fuel / emissions systems:

Is it possible for the codes:

P0137: high voltage O2 sensor
P0138: low voltage O2 sensor

To cause the car to run in a rich condition? From my understanding the secondary O2 sensor is only to verify the functionality of the catalytic converter and has no authority over the fuel mixture.

The dealer is trying to tell me that even the secondary sensor throwing a code will cause the engine to richen up the mixture. To me this sounds wrong, but perhaps I am mistaken.

 

I'm no authority, but I think you're correct.

 

yeah im pretty sure only the primary o2 will cause that

 

This is a good read that might help. I would replace both sensors.

http://www.picoauto.com/applications/lambda-sensor.html

 

You are correct. A faulty o2 sensor in your cat will not affect your a/f mixture. It is there to basically tell the ecu if the cat is doing its job correctly or not.

 

Did you even read this?

"The exhaust gas oxygen sensor (EGO or O2), or lambda sensor, is the key sensor in the engine fuel control feedback loop. The computer uses the O2 sensor’s input to balance the fuel mixture, leaning the mixture when the sensor reads rich and enriching the mixture when the sensor reads lean.

Lambda sensors produce a voltage signal that recognises the amount of unburnt oxygen in the exhaust. An oxygen sensor is essentially a battery that generates its own voltage. When hot (at least 250 °C), the zirconium dioxide element in the sensor’s tip produces a voltage that varies according to the amount of oxygen in the exhaust compared to the ambient oxygen level in the outside air. The greater the difference, the higher the sensor’s output voltage.

Sensor output ranges from 0.2 volts (lean) to 0.8 volts (rich). A perfectly balanced or "stoichiometric" fuel mixture of 14.7 parts of air to 1 part of fuel gives an average reading of around 0.45 volts.

The lambda sensor’s output voltage doesn't remain constant, however. It flip-flops back and forth from rich to lean. Every time the voltage reverses itself and goes from high to low or vice versa, it’s called a “cross count”. A good O2 sensor on a injection system should fluctuate from rich to lean about 1 per second. If the number of cross counts is lower than this, it tells you the O2 sensor is getting sluggish and needs to be replaced.


"

 

He's saying that's not the role of the secondary, which is what the OP is asking. The primary O2 sensory is what is determining A/F ratio. The second one tells you if you have had a catalytic failure/decomposition.

 

The seconday o2 only monitors the cat operation. We all do the spark plug spacer trick when putting in a test pipe, and that doesnt affect anything because we are FOOLING the ecu. The sensor is fully operational.

HOWEVER!!!!

With a faulty secondary o2, the oxygen sensor and catalytic converter monitors will NEVER complete, and THAT can affect your mileage and AF ratio.