Replacing O2 sensors - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


Buick When starting new posts, please specify YEAR, MAKE, MODEL, ENGINE type, and whatever modifications you have made.

Reply
 
 
 
Thread Tools Search this Thread
Old 10-02-2016, 08:41 AM   #1
Junior Member
Posts like a Ricer Type-R
Thread Starter
 
tbdxb's Avatar
 
Join Date: Sep 2016
Location: Dubai/UAE
Posts: 13
Thanked 1 Time in 1 Post
tbdxb is on a distinguished road
Default Replacing O2 sensors

Hi,

I have a question regarding replacing O2 sensors on a '96 Buick PA (base). One of the sensors (downstream, after the cat) is shot and need to be replaced. I read somewhere that it is recommended to replace the other sensor (upstream, before the cat) as well, to avoid imbalance of data into the PCM and thus low engine performance. Is that correct?

Has anyone a recommendation?
I am looking at the ACDelco pair (AFS75/AFS123) at about 40 bucks each at RA.

Thomas
tbdxb is offline   Reply With Quote
Old 10-02-2016, 08:49 AM   #2
Senior Administrator


Certified Car Nut
 
Mike's Avatar
 
Join Date: Jul 2003
Location: Elmira, NY
Posts: 15,545
Thanked 956 Times in 749 Posts
Mike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond repute
Default

The upstream sensor is really only there for the computer to monitor fueling conditions(fuel trims). The downstream sensor is only used to see if the cat converter is working or not.

The only real benefit of changing the upstream sensor is if you have a diagnostic scanner that can reset the learned fuel trim values your ECU has stored. Otherwise, changing the upstream would be moot.
Mike is offline   Reply With Quote
The Following User Says Thank You to Mike For This Useful Post:
tbdxb (10-02-2016)
Old 10-02-2016, 09:00 AM   #3
Junior Member
Posts like a Ricer Type-R
Thread Starter
 
tbdxb's Avatar
 
Join Date: Sep 2016
Location: Dubai/UAE
Posts: 13
Thanked 1 Time in 1 Post
tbdxb is on a distinguished road
Default

Mike,

thanks for the advice.

Quote:
Originally Posted by Mike View Post
The upstream sensor is really only there for the computer to monitor fueling conditions(fuel trims). The downstream sensor is only used to see if the cat converter is working or not.

The only real benefit of changing the upstream sensor is if you have a diagnostic scanner that can reset the learned fuel trim values your ECU has stored. Otherwise, changing the upstream would be moot.
So, since the upstream sensor is working it is better left untouched?

What would be the effect of not replacing the downstream sensor?
I understand that it measures the O2 concentration in the exhaust gas so that the PCM is adjusting the injected fuel accordingly. Now, since the sensor doesn't report any value, does the PCM use a fallback program with assumed O2 values? Or does it estimate the values based on the upstream sensor?

Thomas
tbdxb is offline   Reply With Quote
Old 10-02-2016, 09:05 AM   #4
Senior Administrator


Certified Car Nut
 
Mike's Avatar
 
Join Date: Jul 2003
Location: Elmira, NY
Posts: 15,545
Thanked 956 Times in 749 Posts
Mike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond repute
Default

No, the downstream sensor is only used to see if the cat converter is working. It only reports a possible problem with the cat, that'* it.

If the upstream sensor(one that monitors fuel trims) fails, the ECU uses a different data map to follow. That'* when fuel economy suffers.
Mike is offline   Reply With Quote
Old 10-02-2016, 09:39 AM   #5
Junior Member
Posts like a Ricer Type-R
Thread Starter
 
tbdxb's Avatar
 
Join Date: Sep 2016
Location: Dubai/UAE
Posts: 13
Thanked 1 Time in 1 Post
tbdxb is on a distinguished road
Default

So if I drive for with the downstream sensor not working, there would be no effect like low performance or high fuel consumption? Hence, it would not be the most urgent item to replace.

T.
tbdxb is offline   Reply With Quote
Old 10-02-2016, 09:42 AM   #6
Senior Administrator


Certified Car Nut
 
Mike's Avatar
 
Join Date: Jul 2003
Location: Elmira, NY
Posts: 15,545
Thanked 956 Times in 749 Posts
Mike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond repute
Default

Correct. But if its constantly throwing a code, it may throw the system into a hizzy and may not monitor somethings. ECU'* are weird like that. Tis best to just replace it. Especially if you have to get it inspected.
Mike is offline   Reply With Quote
The Following User Says Thank You to Mike For This Useful Post:
tbdxb (10-02-2016)
Old 10-02-2016, 09:53 AM   #7
Junior Member
Posts like a Ricer Type-R
Thread Starter
 
tbdxb's Avatar
 
Join Date: Sep 2016
Location: Dubai/UAE
Posts: 13
Thanked 1 Time in 1 Post
tbdxb is on a distinguished road
Default

Quite, thanks.
I guess one cannot do much wrong with the ACDelco AFS123. It is 40$ at RA.
T.
tbdxb is offline   Reply With Quote
Old 10-02-2016, 01:11 PM   #8
Senior Administrator


Certified Car Nut
 
Mike's Avatar
 
Join Date: Jul 2003
Location: Elmira, NY
Posts: 15,545
Thanked 956 Times in 749 Posts
Mike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond reputeMike has a reputation beyond repute
Default

Your welcome
Mike is offline   Reply With Quote
Old 11-18-2016, 05:58 AM   #9
Junior Member
Posts like a Ricer Type-R
Thread Starter
 
tbdxb's Avatar
 
Join Date: Sep 2016
Location: Dubai/UAE
Posts: 13
Thanked 1 Time in 1 Post
tbdxb is on a distinguished road
Default

Finally, I can give a feedback on this. Replaced both O2 sensors, upstream and downstream. Also reset the fuel trim history (actually, workshop has done it).

At first the motor ran really really bad, but a after half hour or so it leveled out. Now after about 10 hours or so operating, the motor runs really smooth, the slightly rough idle is gone. Also, power returned.

This is the picture of the downstream sensor we pulled out. Looks like it didn't measure anything, but it didn't throw a code either.


Attached Thumbnails
Replacing O2 sensors-80-bpao2s_1407fe4704fddf25c68272c9978c76fb3fe76415.jpg  
tbdxb is offline   Reply With Quote
Old 11-18-2016, 07:57 AM   #10
Senior Member
True Car Nut
 
rjolly87's Avatar
 
Join Date: Jun 2003
Location: Las Cruces, NM
Posts: 6,824
Thanked 284 Times in 234 Posts
rjolly87 has much to be proud ofrjolly87 has much to be proud ofrjolly87 has much to be proud ofrjolly87 has much to be proud ofrjolly87 has much to be proud ofrjolly87 has much to be proud ofrjolly87 has much to be proud ofrjolly87 has much to be proud ofrjolly87 has much to be proud ofrjolly87 has much to be proud of
Default

What symptoms were you having that prompted replacement? Just the catalyst code?
rjolly87 is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Replacing the o2 sensors BennitoCruz Oldsmobile 4 12-01-2012 10:27 PM
how many O2 sensors in a Series I? 93-SSEI- General GM Chat 18 03-06-2003 05:00 AM
Bosch O2 sensors.. the low down?? delta88 1992-1999 8 03-01-2003 03:24 PM
New Techinfo Topic - O2 sensors willwren 1992-1999 6 02-07-2003 02:48 PM
O2 sensors Dylansdad 1992-1999 1 11-04-2002 10:37 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 07:33 AM.