bad o2 sensor = ??

[Bwana]

What does a bad o2 sensor do to performance, specifically HP and gas mileage?

[SVXelerator]

There's a good chance your air-fuel mixture will be "off" - more than likely too rich or too lean. If you see a significant change in your gas mileage the O2 sensor is a good place to start looking.:eek:
(better yet-- a bad one should throw a code...)

[yeahyahoo]

So what kind of code ? My check engine light sometimes would not go on when cold start, but will stay there after the first start-up. I am suspecting it is from O2 sensors....

[lee]

Originally posted by Bwana
What does a bad o2 sensor do to performance, specifically HP and gas mileage?

stolen from somewhere on the web....

Typically, a bad O2 sensor will read low (lean), which causes the engine to run too rich, pollute too much and use too much gas. A low reading can be caused by several things: old age, contamination, a bad wiring connection, or an ignition or compression problem in the engine.

As an O2 sensor ages, it doesn’t react as quickly as it once did. The increased lag time makes the sensor sluggish and prevents the engine from keeping the air/fuel mixture in close balance. If the engine burns oil or develops an internal coolant leak, the sensor element may become contaminated causing the sensor to fail.

Because the sensor reacts to oxygen in the exhaust and not fuel, any engine problem that allows unburned air to pass through the cylinders will also trick an O2 sensor into reading lean. A misfiring spark plug or a leaky exhaust valve - even a leak in the exhaust manifold gasket - may allow enough air into the exhaust to screw up the sensor readings. It won’t damage the sensor, but it will create a rich running condition that hurts emissions and fuel economy.

[n00b on demand]

I wonder if my hesitation problems could be because of a bad o2 sensor...the hesitation has gotten much better with the K&N filter for some reason. My CE light did flash twice in the summer for 1 second.

[Bwana]

Cool, thanks guys. I had the code read, and it said O2 sensor, that's why i was asking...so i KNOW it's the o2 sensor.

Just wondering what actually happens when it's bad.

Now that I think about it, my gas mileage probably is worse. I'm getting about the same miles per tank in my 96 as i was in my 94...but on the 96 all of my miles are highway. :eek:

Thanks again.

[Chiketkd]

Originally posted by Bwana
Cool, thanks guys. I had the code read, and it said O2 sensor, that's why i was asking...so i KNOW it's the o2 sensor.

Just wondering what actually happens when it's bad.

Now that I think about it, my gas mileage probably is worse. I'm getting about the same miles per tank in my 96 as i was in my 94...but on the 96 all of my miles are highway. :eek:

Thanks again.
Bwana,

You have a '96 SVX with an OBDII system like myself.

This code you got for the O2 sensor, is it for one of the front two sensors, or for the third sensor? The front two sensors actively communicate with the ECU to adjust the afr to optimum.

The third sensor can be deleted with out having any affect on performance. Several WRX/STI guys have done this with an O2 simulator from Perrin (allows the entire cat to be removed and a straight-pipe installed).

-Chike

[Beav]

Originally posted by Chiketkd

... with an O2 simulator from Perrin (allows the entire cat to be removed and a straight-pipe installed).

-Chike

Otherwise known as a half-dead AA battery?

[SilverSpear]

there is something I cannot understand... I don't have O2 sensors in my car, my gas mileage is very good (16mpg), how come?

[Bwana]

Originally posted by Chiketkd

Bwana,

You have a '96 SVX with an OBDII system like myself.

This code you got for the O2 sensor, is it for one of the front two sensors, or for the third sensor? The front two sensors actively communicate with the ECU to adjust the afr to optimum.

The third sensor can be deleted with out having any affect on performance. Several WRX/STI guys have done this with an O2 simulator from Perrin (allows the entire cat to be removed and a straight-pipe installed).

-Chike

I'm at school right now, and the paper work and stuff is at home...but if I had to take a guess at which one it said...it would be....
i thought it said something to the effect of bank 3 row 1...or row 3 bank 1? i have no idea, ill look tomorrow when i go home. :confused: :D

[Chiketkd]

Originally posted by Bwana
I'm at school right now, and the paper work and stuff is at home...but if I had to take a guess at which one it said...it would be....
i thought it said something to the effect of bank 3 row 1...or row 3 bank 1? i have no idea, ill look tomorrow when i go home. :confused: :D
Definitely check. I'd also be interested in knowing which exact code you got.

-Chike

[SEA Sleeper]

During lecture today we had a discussion on how pre-OBDII cars ('95 and below) can set an O2 Sensor code because of a failing MAF.

Originally posted by SilverSpear
there is something I cannot understand... I don't have O2 sensors in my car, my gas mileage is very good (16mpg), how come?

Are you joking? 16 mpg is not good. Does your car have Catylitic converters or any emissions equipment for that matter? O2 sensors are an intregal part of Fuel delivery and metering; for your car to simply not have them is very perplexing. :confused:

[Chiketkd]

Originally posted by SEA Sleeper
During lecture today we had a discussion on how pre-OBDII cars ('95 and below) can set an O2 Sensor code because of a failing MAF.

Are you joking? 16 mpg is not good.
Or from a failing fuel pump which could also cause a lean condition... ;)

-Chike

P.S. I have to agree, 16 mpg is not good even if you're doing all city driving. Should be at least 3-4 mpg better.

[Beav]

Those are both reasons why trotting down to the local parts store and buying parts based on the codes pulled are NOT a good idea or in one's best financial interest. Codes are just a starting point in diagnosing a problem.

[Bwana]

Ok, it was code:
P0145 - O2 Sensor Circuit Slow Response (Bank 1 Sensor 3)

[Chiketkd]

Originally posted by Bwana
Ok, it was code:
P0145 - O2 Sensor Circuit Slow Response (Bank 1 Sensor 3)
Holy cow, I pulled that same code this week for the first time on my SVX as well. :eek:

From hanging with Tom (Svxfiles) today and talking to him about the code, the O2 sensor at fault is the third one (behind the transmission). Per Tom, this 3rd O2 sensor isn't used by the ECU to change the afr, but to monitor how efficiently the first two O2 sensors are working (for emissions).

The code is basically saying that it is taking a longer time than specified for your O2 sensor to take a reading. This is probably an indication of age, but could also mean that there's a bunch of crud coating it.

Tom used an appropriate sized wrench and undid the third O2 sensor, cleaned it off with throttle body cleaner, let it air for a while and popped it back in. I'll see if I get the code again. If so, then I'll just get a new O2 sensor later on in the Spring...

-Chike

[SVXRide]

Chike,
If I read you right, this means that there is the chance that if you pull this same code again that one of your primary O2 sensors is "going away"? By this, I mean that it appears that the 3rd O2 sensor is there to just monitor the job the two primary O2 sensors are doing, which means that either it has gone bad or it is still good and one of the primary O2 sensors is actually on its way out.
Note: I noticed in a picture in your axle replacement thread that the leads coming out of your primary O2 sensors are different - thus leading me to believe that at least one of them has been replaced at one point in time.
-Bill
p.s. did you or Tom happen to measure the resistance on the O2 sensors while you had the car up on the lift?

[Chiketkd]

Originally posted by SVXRide
Chike,
If I read you right, this means that there is the chance that if you pull this same code again that one of your primary O2 sensors is "going away"? By this, I mean that it appears that the 3rd O2 sensor is there to just monitor the job the two primary O2 sensors are doing, which means that either it has gone bad or it is still good and one of the primary O2 sensors is actually on its way out.
Note: I noticed in a picture in your axle replacement thread that the leads coming out of your primary O2 sensors are different - thus leading me to believe that at least one of them has been replaced at one point in time.
-Bill
p.s. did you or Tom happen to measure the resistance on the O2 sensors while you had the car up on the lift?
Bill,

I'm not sure if pulling this code indicates a problem with one of the front two O2 sensors, as they would trip a code on their own. It just seems like something is up with the third O2 sensor that's causing it to take a longer time to get a reading.

Both of my primary O2 sensors were replaced by the dealership I bought the car from last April. I got the receipts for the replacement when I bought the car. As far as I know, they're the same, but one of the 'sheaths' that covers the wires doesn't stay down over the lower wires like the other one...

We didn't measure the resistance of my O2 sensors, btw...

-Chike

[SVXRide]

Chike,
Ah, the old "sheath pretending to be insulation" trick!:p
Given that the dealership replaced both of the primaries for you, I'm with you on the 3rd sensor just acting up on you. Hope cleaning it up does the trick!
-Bill

[Myxalplyx]

Holy cow, I pulled that same code this week for the first time on my SVX as well. :eek:

From hanging with Tom (Svxfiles) today and talking to him about the code, the O2 sensor at fault is the third one (behind the transmission). Per Tom, this 3rd O2 sensor isn't used by the ECU to change the afr, but to monitor how efficiently the first two O2 sensors are working (for emissions).

The code is basically saying that it is taking a longer time than specified for your O2 sensor to take a reading. This is probably an indication of age, but could also mean that there's a bunch of crud coating it.

Tom used an appropriate sized wrench and undid the third O2 sensor, cleaned it off with throttle body cleaner, let it air for a while and popped it back in. I'll see if I get the code again. If so, then I'll just get a new O2 sensor later on in the Spring...

-Chike

Old school bump!
Pulled this code today from my SVX:
P0145 - O2 Sensor Circuit Slow Response (Bank 1 Sensor 3)

I did recently have 3 spots on my exhaust system leaking from welds when this code was active. They have since been repaired. I just reset the computer about 10 minutes ago. Will consider removing this O2 sensor, cleaning and re-installing rather than replacing. Just bumping as a reference so I can find this thread easier.

[dennyo]

i've been dealing with this code for about a year now. i replaced the front (right)sensor and the rear as well. tried the battery disconnect clear routine.didn't work. tried taking the harness from the rear sensor to the block off and cleaned it.didn't work. tried cleaning the tip of the sensor. didn't work. both sensors are bosch oe fit btw. sure would like to know what the problem is. i'm getting tired of erasing the cel every time it comes on:lol:

[Rod.]

Have had my SVX for less than a week and it keeps throwing this code as well. Tried the cleaning repair but no luck. I guess a r/r is next unless someone can suggest something else to try first.

Thanks.