O2 sensor

One more post while I'm on a roll ...

2003 OBS, 190000kms.

My check engine light has been on about a year now. I checked it out then, it was front o2 sensor. Car was working fine, same gas mileage as day 1, so I let it go. No change in performance since then.

I figure if the front sensor is gone, replacing it will result in a message that the rear one is also gone. Replacing both will probably lead to a message that the cat is gone. I'm afraid of a domino effect so I left it alone.

I recently had to replace a section of that exhaust pipe (cracked at the brace), and the mech told me that if the o2 sensor isn't working, the engine could be running rich and that could ruin the Cat.

So, my question is: What symptoms would I have if the car was running rich?

Thanks.

Loss of fuel economy is the most easily observed symptom. If you have been getting around, say, 27 -28MPG, and this drops off to 24 or

25MPG, that would be about typical. Black sparkplug electrodes, black, sometimes black and wet-looking deposits at the tail pipe, and in extreme cases, a smell of gasoline in the exhaust, are as well. Unless things are to the "gas-smell-in-the-exhaust" point, you are unlikely to notice much loss of performance, tho.

And your wrench is quite correct; a bad front O2 sensor will cause the engine to run in "limp" mode, which is deliberately rich to avoid possible damage. Operating the vehicle in this mode for very long will decidedly ruin your catalytic converter. If you've been running in limp mode for a year, tho, it's already toast, and you probably have a whole string of OBDII codes regarding the O2 sensors, and catalyst efficiency.

At this point, your best bet will to see if you can find a Y pipe (?? . . . Whatever components hold the CAT and O2 sensors on the '03 car. I _think_ they're all in the Y pipe. Anyone?) at a salvage yard. Technically, I don't think they are supposed to sell used emissions control components, but probably if you ask nicely, AND ask for an "exhaust Y pipe" rather than "the catalytic converter", you'll be able to land one. Swap in the whole shebang and be sure to reset the ECU before driving far.

Hope this is helpful.

ByeBye! S.

Steve Jernigan KG0MB Laboratory Manager Microelectronics Research University of Colorado (719) 262-3101