I'm driving a 2000 4x4 4.3 Blazer; a few months ago I had a new cat installed, along with 3 new O2 sensors.

Not long after, the Service Engine Soon light started coming on and going off at fairly regular intervals [100 miles] Now the lights on more often than not.

I had the code run at Advance Auto - P0146 and P0147 - both malfunctioning sensor on Bank 1 Sensor #3.

I can't believe that the sensor would be damaged already, and I'm wondering if it wasn't installed properly [the cat was installed by a garage, the sensors by the previous owner]. They look fine visually when I checked, but I wouldn't know if the wires had been connected wrong, etc.

I wondered if anyone knew what the best course of action is? I don't really want to drop hundreds of $$ at a dealer when I'm not convinced the sensor is damaged. If anyone has any tips for checking over the one I already have to determine if it really is working or not, I'd be really grateful.

Many thanks in advance,

Andy

 

Welcome to the forum.
Unfortunately the easiest way to check your O2 sensor would be to replace it with a new one.
It's either that or get a scanner hooked up to it and check the cross counts.
If you can replace the sensor yourself, that's your best bet.
What brand were these (brand new) O2 sensors, do you know? And what's the warranty on them?

 

Thanks for the reply Chevy Lover -

It would be hard to track down the brand/warranty information, but your second comment reminded me that when I was about to get the car inspected for emissions, the mechanic told me that all three sensors were registering on the scanner; however, at the time, I think the code that ran was for a lean system rather than p0146/p0147 for sensor inactivity. I'm guessing the two are connected....but I'm not mechanically inclined enough to figure it out.

What if i were to switch the #3 sensor with - lets say - the #2 sensor. If the code transfers to the #2, I guess that would indicate something was indeed wrong with the sensor. If the code stayed in the same unit, it would be something else. Is that too naive...

I'm also not sure which sensor #3 is - the one up front on the drivers side, the one opposite it on the passenger side, or the one towards the rear on the passenger side - I guess that would be a good starting point! I'm assuming its the one closest the rear...but not certain....

Thanks again for your help, its much appreciated to a grad school student strecthing a measly TA stipend

If I can resolve the problem, my wallet would also appreciate the the extra MPG. I'm getting about 13mpg best around town right now, and getting the slightly sluggish reaction and dim noise I'm reading can often be associated with a bad 02 as well.

Andy

 

Not a bad idea to swap them around, as long as the connectors are the same. Clear the codes before you run it after swapping.

[IMG]local://upfiles/2910/E43ECABCE8344D74862E787B425EF6FF.gif[/IMG]

 

Great stuff - the diagram was great, at least I now know which one I'm dealing with

I may also see if I can get a second hand one from a junk yard, rather than messing aound switching them....

If I do install a new/used sensor, will I still need to get that code reset or will it take effect itself after a few drive cycles. I don't want to give the mechanic the pleasure of taking my $40 to press a button if I can help it

Thanks again - a huge help!

Andy

 

I don't know how many cycles are required to clear the code. Just disconnect the battery for a couple of minutes. A new sensor probably isnt very expensive. If you get a used one, you are gambling.
Check prices before you decide.

 

definitely swap sensors before coughing up the cash for a new one.

iirc, #3 is the post-cat sensor.

 

I was thinking I might just get a mechanic to run a scanner on it and get the actual values read on each scanner to see if its totally dead, and therefore needs replacing, or if it is reading and there is something else at play here.

Any ideas how much I should reasonably expect to pay for that? Surely it can't take them that long....

I was also thinking that #3 would be post-cat, but Chevy Lover's diagram above seemed to suggest it was pre-cat, on the passenger side, at the join in the Y-pipe. Obviously I'm tending to go with the diagram as being most reliable, but it may be another reason to get it scanned and located for sure by a garage first.

Any thoughts?

Thanks again,
Andy

 

No, B1S3 is the post cat sensor. What was used for the CAT when it was replaced (OEM replacement, high flow aftermarket???)? Some aftermarket cat's can cause this exact problem. In that picture posted above, '2' == B1S1, '3' == B2S1, and '1' == B1S3. If this were a '96/'97 pickup, then there would be an additional O2 sensor directly infront of the CAT which would be B1S2.

Also, what brand O2 sensors were used? I would not recommend anything but AC Delco sensors in GM vehicles. If the replacement sensors were Bosch, I'm betting that the sensor is the problem. They are notorious for being lazy out of the box. You'll typically see this on the upstream sensors (B1S1, B2S1) than on the down stream sensors, but it all depends on how bad the sensor was to begin with.

 

Thanks again for the further help. The CAT was an aftermarket, and it was a real pain in the *** to find; took weeks of searching. Given that, I do have a feeling that its the CAT causing the problem and not the sensor. The problem arose fairly soon [few weeks] after the CAT was installed, and over the past 5 months the only thing thats has changed is that the light is staying on for longer and longer periods of time.

However, the CAT was installed by a trusted mechanic friend who said the job had gone fine and that he didn't see any problems with the installation. I believe the sensors were Bosch.

Any opinions on the best course of action still?

If its not the sensor, I'm at a total loss of where to head next. The only codes being pulled are still P0146 and P0147.

Much appreciated,

Andy