Lean To Rich Threshold Sensor Voltage

Asked by Feb 22, 2016 at 02:42 PM about the 2000 Chevrolet Cavalier LS Sedan FWD

Question type: Maintenance & Repair

Hi, I have a Chevy Cavalier, and I have
been getting bad gas mileage for the past
couple weeks. I normally get around low
30mpg. Now I have been getting about
20mpg. I got my engine scanned in case of
any problems. There was two things that
showed up. The first one said that the car
has an EVAP system leak. And the second
one said Lean To Rich Sensor Voltage. I
already know what the EVAP leak is. I just
need a new gas cap to fix that problem.. I
just need help on trying to figure out what
exactly the lean to rich sensor is, and how
to fix the problem. I just hope it won't be
an expensive fix.

13 Answers


Do you remember the code set for the lean rich condition? Chances are it would be the 02 sensor. I would like to verify.

Best Answer Mark helpful

All it said was TID: $02 CID: $06 Lean To Rich Sensor Threshold voltage (constant) Min: 32,798 Current: 32,768. I don't know if that's the code or not. That's all it displayed on the OBD2 scanner


Ok, that must be a decent scanner. Those are the levels of what the sensors are reading. There is a code page somewhere in there (scanner)

It is an electric scanner. It didn't give me a specific code.


Did the scanner plug into the ALDL connector under the dash? Thats where you would read the codes from, You can go to Auto Zone and have the codes read, it would help knowing the codes.

Ya, that's where I plugged it into. Since the scanner is electric, there's an app for the OBD2. I couldn't find any specific codes from the app. I'll try O'Reillys cuz that's the closest place to me. Do you know if they scan engines for free?


I would say they do, in my town there is a O'Reillys right next to Auto Zone who scan for free. They would loose a lot of business if they didn't. Just see it there is any codes, and post them back here.

I went to O'Reillys yesterday and I got them to scan my engine. The guy gave me one code that was for my evap leak. He didn't give me any other codes. He just said my O2 sensor is bad.


Ok then, between the 02 sensor and the EVAP leak, thats were your mileage went. The 02 is part of what controls the air/fuel mixture, lean, rich, the EVAP is not circulating the gas fumes from the gas tank back to the intake manifold to be burned off. EVAP not so much a big deal other than in mileage, and you wouldn't pass a emissions test, as with both of these bad you wouldn't pass.

I went to a shop last summer because my engine light was on and I wanted to do a check up on my car. The mechanic told me the EVAP leak is just my gas cap. My gas mileage hasn't changed since my EVAP leak started. I'll buy a new gas cap soon just to make sure it's the gas cap and nothing else. When I was at O'Reillys, the guy told me a new O2 sensor would cost between $30-$50. I will try to get that O2 sensor replaced early in the spring time when I save some money to be able to do it.


Sound good, the 02 at this point is the biggest problem, and on the (EVAP, gas cap if it is a small leak, po442), EVAP system gross leak, which is the purge system, po455, would be the code showing up.

Did you ever get this issue resolved? I am having the same issue and same readings on mine.

Sorry, I haven't found out anything yet. I have been planning to get a new O2 sensor for my car a few months ago, but I haven't had time to get it done. I can try to get one soon and I'll let you know if that solves my problem.

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