: O2 sensor vs. "check engine" light



Serobin88
04-12-05, 08:23 PM
I notice my gas mileage is about 16.5 mpg. Should be closer to 19 mpg. I went to a parts store. I had the engine checked with their hand-held scanner. o2 sensor 2 in bank 2 [right side, after converter] showed a code of "no activity". Yet, the Check Engine light had never, and still has not come on at all.

I went back another day to verify before buying the o2 sensor in question. They scanned again. Result was "pass"--meaning no o2 sensor problem.

Could an o2 sensor be going bad, causing low gas mileage, and yet act this way.....no Check Engine light, and showing itself, or not showing itself to scans?

Serobin88
04-12-05, 08:28 PM
As an afterthought, I know that low gas mileage can be caused by a bad PVC valve or hose. Does the Catera even have a PVC valve?

Vesicant
04-12-05, 09:42 PM
I notice my gas mileage is about 16.5 mpg. Should be closer to 19 mpg. I went to a parts store. I had the engine checked with their hand-held scanner. o2 sensor 2 in bank 2 [right side, after converter] showed a code of "no activity". Yet, the Check Engine light had never, and still has not come on at all.

I went back another day to verify before buying the o2 sensor in question. They scanned again. Result was "pass"--meaning no o2 sensor problem.

Could an o2 sensor be going bad, causing low gas mileage, and yet act this way.....no Check Engine light, and showing itself, or not showing itself to scans?

What year is your Catera? It might be time for a tuneup, new airfilter or in your case it may need a new o2 sensor; they're not always consistant.

Could be dirty injectors or a dirty fuel system as well.

acecody
04-13-05, 11:08 AM
Catera's are famous for having all or any of the dash lights burn out, before you start the engine when the key is clicked to the on position, make sure it comes on then during the dash light test, it might be burned out.

Serobin88
04-14-05, 08:10 AM
1997 Catera.
All the dash lights DO work. I recently replaced the air filter. I do not need a tune up, as per the dealer service personnel where 6 months ago I replaced the spark plug coils/cables and valve cover gaskets. Have put BG 44K in last tank of gas to clean injectors if that is the problem.

Still, the gas mileage is on the low end of the range for the car. And the o2 sensor code was "no activity" once out of three scans. No Check Engine has ever come on, although that indicator does functions. (I was really looking for an ABS light code readout when I had the first scan done. Two follow up scans a week or so later showed "pass".)

1> Does anyone know if the Catera has a PCV valve? I could not find one mentioned anywhere in the GM manual for the car--which is very technical and over my head, anyway.

2> And does anyone think that if the o2 sensor scanned once as bad, even though subsequently scanning good twice, it could still be malfunctioning? And could it be malfunctioning without triggering the Check Engine indicator?

AllenPacla
04-14-05, 11:00 AM
Do you know specifically what is the function of that O2 sensor in question? I believe it's Omermurat who said that the Catera itself has about 4 O2 sensor, I don't think that one of them malfunctioning would cause the engine to use up gas. I myself had my car scanned when after i replaced the burnt bulb of the "Check Engine" light it suddenly is lit up. I had the same code as you do plus another one. And I checked the price of that O2 sensor and it cost more than 300 dollars from Autozone. If it has really a direct connection with the fuel delivery of the engine then i think it's worth the money in the long run. But if not, forget about it.

Serobin88
04-15-05, 08:54 AM
Thanks, Allenpacla. Yes. There are 4 sensors. There are two exhaust manifolds and two catalytic converters. There is an o2 sensor in front of each c-converter, and one after each c-converter. The one-time scan fail was for the passenger side o2 sensor that is after the convert--gases now on their way to the muffler.
ATTN! Go to gmpartsdirect.com for immense savings on parts for Cateras. You may need GM part numbers to get price quotes. You can get those off another site such as a big dealer that sells parts via internet.