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02 sensor can affect.... ?

3K views 23 replies 7 participants last post by  pooskay 
#1 ·
My check engine light popped up the other day....90k miles ... seems like the common reason for the check engine light coming on is due to a bad 02 sensor. But can this cause a loss in power? My acceleration is not what it used to be. Thanks for the feedback.
 
#2 ·
the o2 sensor shouldnt cause a noticiable drop in power, but im not sure. Loss of power is usually the result of engine compression loss or a dead cylinder.
 
#4 ·
A faulty O2 sensor can do many higns to your car and poor performance could be one thing. The O2 sensor sends bad info to the ecu and you air/fuel ratios are screwed up, very likely problem.
 
#5 ·
I would have the fault codes checked. Especially with 90K on the odometer. I would suspect a clogged catalytic converter.
 
#6 ·
..and by the way, I would also replace the O2 sensor as well.
 
#7 ·
Originally posted by pooskay@Dec 15 2003, 08:12 AM
My check engine light popped up the other day....90k miles ... seems like the common reason for the check engine light coming on is due to a bad 02 sensor. But can this cause a loss in power? My acceleration is not what it used to be. Thanks for the feedback.
it will affect power because the car is essentially running in safe mode (like a computer sort of) because the signal is bad to the DME the car runs the car in a sort of "safe mode" where the car purposely dumps more fuel into the car then normal to compensate for any possible situation that the car could run without the readings of the O2 sensor. this is why its typical to notice poor fuel mileage and somewhat poor performance .
 
#11 ·
Have you noticed any rotten smell from the car/exhaust, like a rotten egg or sulfur smell?
 
#12 ·
no, but its giving off a very heavy fuel smell when i start it up....a couple times when i started my car (cold start), the engine shook/vibrated for about 5 seconds and struggled to reach a stable rpm..seemed like it was going to shut down, but never did.... but that only happened twice out of many starts.
 
#13 ·
See this is where it can get costly and difficult because while the 02 sensor is a likely cause, there are also many other possibilities that lurk. Another possibility is the crankcase vent valve or any type of vac. leak. The fuel smell could be because of either. If there is a vacuum leak or a bad maf (any type of lean condition) then the DME is going to correct this by dumping more fuel which will cause the 02 sensor to go frantic. Same possibility with a coolant temp sensor. All the added fuel will then create the fuel smell. However, a bad catalytic converter can do the same just in a slightly different fashion. I could go on and on, just too hard to quickly diagnose the problems that you're having without fault codes.
 
#15 ·
undefined meaning what? did it just say "undefined" or was there anything else along with it??
 
#16 ·
and bmw shop looked at my car before regarding the fuel smell. they said my secondary air pump and fuel valve needed to be replaced. havent replaced it yet cuz they're charging 600 somethin $$ , and because the sec air pump only functions at startup for the first couple minutes or so....correct??
 
#18 ·
Here in lies the problem... possibly. True about the secondary air pump. However, the purpose of the secondary air pump is to pump air into the raw unspent gases to reduce emissions. By not doing this at all or not enough, the O2 senor is seing far too much raw fuel which can ruin the O2/fail premature and even destroy the catalytic converter. The DME is programmed for specific parameters and everything is designed to work as a system. Basically the O2 is looking for a preset range of A/F ratios and CO2 content and not seeing it. This would possibly explain the "undefined" code because that diagnostic may be too complex for your tech's diagnostic tool. Now, I am not saying for sure that this is your problem but it would be highly suspected.
 
#19 ·
hmmm sounds very logical and VERY possible...i will take it in for a second opinion, and i'll have your explanation in mind ...thanks a lot.

hopefully replacing the secondary air pump w/fuel valve and 02 sensor will solve my problems, cuz i miss the power i used to have! spark plugs and air filter are new..hope its not a vac leak.
 
#20 ·
well i promised an update on this issue.... and Extech...you were right....the cause of the check engine light was due to a bad secondary air pump! the O2 sensor appears to be fine....bro is still working on replacing the air pump + check valve..so we'll see if it affects the performance, but i doubt it, cuz i've read the secondary air pump does not have anything to do with performance...is this correct?
 
#22 ·
it shouldn't have any effect on the performance unless the O2 sensor has been affected or if you have a problem with the cat. However, if there is a vacuum leak letting un-metered air into the system then you could have performance issues there as well. Were there any more fault codes? The thing to do would be after the pump is replaced then have the codes pulled again. So unless for some reason the pump was running when it wasn't supposed to and screwing with the 02 sensor's readings then it shouldn't have an effect.
 
#23 ·
Thanks Furious !
 
#24 ·
first off, thanks again Extech for all the great feedback....

ok now i have another problem, well my bro replaced the sec air pump w/ no problem ...everything worked fine....but when i started it up, the damn auto transmission light popped up (exclamation symbol) ...i turned the car off...waited...then turned it back on...light went away...but then after another start..the light comes up...so i drove it and it was jerking between 2nd and 3rd gear and also when downshifting (i didnt dare to drive it past 3rd gear)...turned the car off again...started it back up and it drove fine w/no warning light.

well for some reason, my bro disconnected the battery when replacing the pump, and i've read that a common fix for the transmission light is to clean the battery terminal and check battery conditions...so we checked the connections again, made sure the connections were secure, we started it and so far no light has popped up..but im getting a feeling it will happen again...have you ever come across a problem like this...it cant be a transmission problem right? cuz its happening on and off...maybe its a malfunction in the shifting electronics?? please help! thanks.
 
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