I've got a problem...

[vix_98_318ti]

I keep getting an Pre-Cat O2 sensor code message and lights up my check engine light. I've already replaced my O2 sensor and after clearing the code, it will come back after about 1 day of driving. Any body have any ideas what may be causing this problem?

thanks

[DustenT]

Originally Posted by vix_98_318ti

I keep getting an Pre-Cat O2 sensor code message and lights up my check engine light. I've already replaced my O2 sensor and after clearing the code, it will come back after about 1 day of driving. Any body have any ideas what may be causing this problem?

thanks

Are you getting any other codes, like for the Secondary Air Pump? What O2 sensor message are you getting? (response time, heater, etc...).

[Etienne]

I was having this same problem with my car... turned out to be the diffa (spl.) unit.

[vix_98_318ti]

The error code I get is 0A - which is related to the Pre-Cat O2 sensor. I was getting really poor mpg (about 15/gl) then I replaced my spark plugs with Bosh 4+. The the O2 sensor was replaced, which did improve my miles slightly. But the stupid "engine light" has come back a couple of times. What exactly did you replace Etienne (diffa spl. unit)? Can you explain that a bit further...not sure what you mean and how much did it cost you and do I have to take it to the mechanic?

thanks

[vix_98_318ti]

bump

ANY HELP??

[Etienne]

Sorry for not getting back to you sooner -- not much time to scour the boards in the past few days.

(more info in my pm, but thought I'd post this here as well in case its helpful to anyone)

Here is basically what happened to me.

CEL was on -- code read out that the oxygen sensor was bad. Took it to a shop (not dealer) and had them replace it.

about a day later the CEL pops back on -- so I go back and find out the other O2 sensor is bad... so they replace that one too.

Then about another day or so the CEL is back on... reading O2 sensor. I reset it... and it stays off for like an hour. Started grad-school in philly so didn't have much time to deal with it. However, my gas mileage was going down the tubes (like 18mpg) so as soon as I could I took the car to the dealer.

Turns out that the diffa (spl.) unit which if I remember correctly controls the heating and maybe the current to the O2 sensors was bad because the shop that put the sensors in spliced some wire wrong. The result is that the the ECU doesn't get a proper signal from the sensors, so it throws an O2 sensor fault.

Dealer had to replace the Diffa and the ECU because both had been damaged by the spliced wire, however, that being done, the CEL is off and gas mileage is back where it should be.

Originally Posted by vix_98_318ti

bump

ANY HELP??

[vix_98_318ti]

Could it be that I have another BAD O2 sensor? I went the cheap route and bought mine at Autozone! It cost me about $80 and it is exactly the same OE part. I'm thinking it might be the problem? Maybe I should buy from a BMW dealer/distributor?

[Etienne]

Its worth a try I suppose. Though if you are spending 80 bucks anyway, it might be worth it to have the dealer test 'em for you. They will probably charge you arou 80-100 bucks for the labor. If it is the plug, I would think that AutoZone would replace it for you and you'd have a new plug. If it isn't, there is a good chance they can tell you what is wrong -- it would suck to buy a new plug and find the CEL is still on...

[GDB]

AutoZone is not going to have any better/worse parts than your BMW dealership. They only cary Bosch O2 sensors.

Did you by chance have autozone pull the codes? If you did, or if they told you an O2 sensor would fix your problems then yes, you are intitled to a refund. Otherwise they will not refund your money.

Seeing as you just replaced the O2 sensor then the problem probably lies elsewhere (a faulty O2 sensor is a possiblity, but very unlikely).

[vix_98_318ti]

Well....I figure this much, if the connector is bad then it could indicate that I still have a bad O2 sensor. But, since there was no splicing of any kind...I doubt the problem is elsewhere. It has to be in the sensor or connector. yes?
Well I am not sure what to do next...I can either buy another sensor or just live with it until I can figure out what is causing my pre-cat O2 sensor to be giving me a faulty code!

Help please!

thanks

[vix_98_318ti]

anyone?

[3DGE]

Well if your getting low miles, try using seafoam on your car, It improved my MPG. Did you put the O2 sensor in right, maybe its loose or just needs to be whiped off.

Also to imporove the cars mpg you could change the filters (fuel Oil and air).

there are tuts you can look up on this site.

[vix_98_318ti]

Done all that pre-maintenance stuff. New filters, oil, plugs but no help.
Where can I get that seafoam?

[3DGE]

Wellit most likely will not fix your o2 issue, but your car should run better, I got my seafoam from napa, it was like 6 or 7$

[Etienne]

Any further luck on this?