My oldest has a 1999 Chevy S10 w/4.3L V6 that only has 67,000 miles on it. The “service engine” light has been coming on intermittently and is now on all the time. I took it to a local O’Reilly’s and had the OBD read and it came back bad O2 sensor (upstream). I figured at nearly 18 years old, I’d just replace them all. The guy said it had 4, 2 upstream and 2 downstream. After looking, I only see 3. 2 are located after the exhaust manifold, before the cat converter and one is located after the cat converter. Am I missing one or is the guy at O’Reilly’s wrong?
I find conflicting info on the internet, seeing posts that say 3 and 4. Trying to get it squared away so he can take it back to school in the next week or so.
If I’d win the lottery, I’d get him a newer truck but…
Those 02 sensors are certainly confusing on that truck! Look carefully at the lower end, bottom, of the driver side manifold. Sometimes the sensor was in the manifold, other times the exhaust pipe itself. You should be able to see all of them from underneath the drivers side. Good Luck.
The one at the passenger side manifold is Bank2sensor1 (B2S1). At the drivers side manifold should be bank1sensor1 (B1S1). Before the converter is B1S2, after the converter is B1S3. Also, there’s really no advantage in changing the sensors unless they’re setting off an SES code (bad).
Yeah, I’m looking hard and still only see 3. That is a lot of stuff crammed into a small space.
I found Denso replacement sensors for $22.00 so I figured I’d replace the 2 upstream sensors since (I am told) that those are the 2 that create issues.
“Apathy is the Glove into Which Evil Slips It’s Hand”, but really, who cares?
Yep, upstream adjusts air/fuel mixture, downstream only monitors effectiveness of converter. I may be wrong, but from reading your original post, I think you’re still missing one? There should be 2 upstream.
Yeah, probably did a bad job of describing. There is one on driver’s side, just after the exhaust manifold, before the Cat. Conv., one on the passenger side, just after the exhaust manifold bit before the Cat. Conv. and one after the Cat. Conv. That is all I can find. I “looks” like 2 upstream and just 1 down.
“Apathy is the Glove into Which Evil Slips It’s Hand”, but really, who cares?
If you have 2 pipes merging into a y-pipe before the cat(only one cat) and then a single pipe to the muffler/tailpipe there will only be three o2 sensors. If you had 2 cats you would need 4, 2 upstream of the cats and 2 downstream.
quote:67,000 miles? That truck is a "Piece". Lot's of good left!
Yeah, the mileage doesn’t concern me, the age does. I try to keep up with any issues with it while it is here to avoid issues when he is down there at school. I hate being at the mercy of a mechanic I don’t know 2 hours away.
Thanks for the the input folks. Ordered 2 sensors last night and should have them installed by the end of the week.
“Apathy is the Glove into Which Evil Slips It’s Hand”, but really, who cares?
If you have 2 pipes merging into a y-pipe before the cat(only one cat) and then a single pipe to the muffler/tailpipe there will only be three o2 sensors. If you had 2 cats you would need 4, 2 upstream of the cats and 2 downstream.
^^^^^
The new sensors sometimes come with a little pack of anti-sieze, if not pick up some and give the new sensors threads a little coat of it. Make life easier on the next replacement. After that at only 67,000 you’ll probably put on a water pump and alternator around 200,000.
“If Bruce Jenner can keep his wiener and be called a woman, I can keep my firearms and be considered disarmed.”
I had the same truck. First new car I ever had. Financed myself at 18 with no co-signer. Phenomenal mechanically and would really go. Interior bits and pieces failed early, radio, speakers, but nothing mechanical. Back when Chevy/GMC made real trucks. The new stuff is so soft.
Good idea on the anti-seize. Hope to keep it running a few more years with minimal expense so my youngest can eventually wind up driving it. I won’t worry so much if he is driving it as it will just be around town stuff and if something breaks I can handle it here. Looking at adding a 4th car to our “fleet” next year. Yeah!!!
“Apathy is the Glove into Which Evil Slips It’s Hand”, but really, who cares?
If you have 2 pipes merging into a y-pipe before the cat(only one cat) and then a single pipe to the muffler/tailpipe there will only be three o2 sensors. If you had 2 cats you would need 4, 2 upstream of the cats and 2 downstream.
If you have 2 pipes merging into a y-pipe before the cat(only one cat) and then a single pipe to the muffler/tailpipe there will only be three o2 sensors. If you had 2 cats you would need 4, 2 upstream of the cats and 2 downstream.
Again, this engine is quite confusing on the placement of 02 sensors, but, I’ve never seen one with two Catalytic Converters, let alone one with two 02 sensors downstream of the cat? What would be the purpose? Just curious.
Yeah, it is 2 pipes merging into one, one catalytic converter.
“Apathy is the Glove into Which Evil Slips It’s Hand”, but really, who cares?
Just a guess, but, I’m assuming, '99, back, design? If so, the “Y” 02 sensor would be the only upstream?
earlier O2 sensors used 4 sensors. one of each manifold to manage air/fuel mixture, then one before and one after the single cat to monitor cat efficiency.
also be ware, O2 sensors are the number one misdiagnosed OBDII code. just because the sensor is giving an error doesnt mean the sensor is bad. if it is an upstream sensor it could be one of a thousand things making the motor run rich or lean(clogged fuel filter, leaking or clogged injector, weak coils, bad plugs, vacuum leak, etc, etc). if it is a post-cat sensor, your cat could be bad.
were there any other codes? did you happen to look at the live data to see what the sensor was reading? I’m here in columbia, you can swing it by and i can hook it up to my computer and give you a better idea if you want(although just replacing a $22 sensor isnt expensive, it can be a pain to replace)
