Rear O2 A activity

[LS ROB]

My sister brought her Cadillac over this evening for an oil change. She also stated that when she get into the throttle a bit, it smells rotten. I immediately think Cats. Does this look like normal rear O2 sensor activity? Looks like it would be a little on the rich side to me but I have 0 experience with rear O2's so not sure if the activity is normal or not. Any info you guys could provide would be appreciated. Just changed oil, air filter, Cleaned the MAF and indexed the slot in the rubber connector with the "stud" of the airbox. Someone had rotated it a good bit and the trims were way leaner than what is in the attached log.

Side story*** I spent about an hour trying to figure out why the OBD and HP tuners couldn't communicate. Found a blown fuse and changed it. It worked... for just a little while. Did some research and found out that the fuse for the Cig. lighter is also the OBD fuse. Looked and again it was blown. Checked the cig. lighter and there was a DIME stuck down in there! Fished it out, changed the fuse and communication commenced LOL. I bet you guys who do this on the daily see some crazy stuff!



Stock cal. if needed.
2008 escalade 6.2.hpt
rear o2 idle.hpl

[2xLS1]

I've seen the coin in the cig lighter many times in the last 20 years. Usually you see the new fuse pop as soon as you plug it in. Go straight the cig lighter socket. The bitch is when it's wedged in there so tight you can't dig it out. Then you have to try and get behind it and unplug it.

[blindsquirrel]

Can't tell you how many times at the dealer I'd get one the Tech2 wouldn't talk to, to find the same thing: owner's kids were using the lighter socket like a slot machine.

If the cats are no good, and the codes aren't disabled, it will set codes. If it's not setting anything they are working well enough that the ECM doesn't think there is a problem, and they are pretty picky about it.

[LS ROB]

I've seen the coin in the cig lighter many times in the last 20 years. Usually you see the new fuse pop as soon as you plug it in. Go straight the cig lighter socket. The bitch is when it's wedged in there so tight you can't dig it out. Then you have to try and get behind it and unplug it.

Luckily, it wasn't that wedged. I took my test probe to it, was able to get it turned vertical and grabbed it with small needle nose pliers.

[LS ROB]

Can't tell you how many times at the dealer I'd get one the Tech2 wouldn't talk to, to find the same thing: owner's kids were using the lighter socket like a slot machine.

If the cats are no good, and the codes aren't disabled, it will set codes. If it's not setting anything they are working well enough that the ECM doesn't think there is a problem, and they are pretty picky about it.

LOL That's wild man! Something so common as a dime causing such a headache. I thought she had some serious problem going on. Anyways, thanks for the input on the rear O2 activity. I'll double check the DTC's to make sure they've not been turned off. As far as I know, this thing has not been fiddled with. Thanks once again!!

[blindsquirrel]

Actually... looking at the log, that L92 is toast. Send it to me and I will make sure it is properly recycled.

[verlon]

My sister brought her Cadillac over this evening for an oil change. She also stated that when she get into the throttle a bit, it smells rotten. I immediately think Cats. Does this look like normal rear O2 sensor activity? Looks like it would be a little on the rich side to me but I have 0 experience with rear O2's so not sure if the activity is normal or not. Any info you guys could provide would be appreciated. Just changed oil, air filter, Cleaned the MAF and indexed the slot in the rubber connector with the "stud" of the airbox. Someone had rotated it a good bit and the trims were way leaner than what is in the attached log.

Rear O2 looks absolutely normal. Downstream loop has a target of 775mV with insensitivity range 750-800mV on domestic vehicles. So anything smooth within 750-800mV range is normal rear O2 activity.

If exhaust smells like a rotten eggs it's likely there is an exhaust manifold leak. Check for loose or cracked exhaust manifold bolts (mostly rear) on both heads.

[edcmat-l1]

Nevermind..........

[TheMechanic]

They (EPA, ARB) want a slight rich mixture on the downstream to reduce NOx. Personally it seems a little rich for a warmed up motor but without doing a little high rpm, loaded, and snap throttles it is difficult to make a snap decision on its "goodness". Whenever I see excessive rich on down-streams I will automatically gravitate towards diagnosing up-streams. Given its later model the internal diagnostics are pretty good.

[edcmat-l1]

They (EPA, ARB) want a slight rich mixture on the downstream to reduce NOx. Personally it seems a little rich for a warmed up motor but without doing a little high rpm, loaded, and snap throttles it is difficult to make a snap decision on its "goodness". Whenever I see excessive rich on down-streams I will automatically gravitate towards diagnosing up-streams. Given its later model the internal diagnostics are pretty good.

It's not rich. It is oxygen deficient. During steady cruise the cat stores O2. On decel it releases it. I have some old scope screen shots of upstream vs downstream and you can watch it happen. I'll see if I can dig them up. Pretty sure there on one of my external hard drives.

[LS ROB]

Actually... looking at the log, that L92 is toast. Send it to me and I will make sure it is properly recycled.

You never linked the address?? Ha!

[LS ROB]

Rear O2 looks absolutely normal. Downstream loop has a target of 775mV with insensitivity range 750-800mV on domestic vehicles. So anything smooth within 750-800mV range is normal rear O2 activity.

If exhaust smells like a rotten eggs it's likely there is an exhaust manifold leak. Check for loose or cracked exhaust manifold bolts (mostly rear) on both heads.

Thank you Verlon!

[PGA2B]

I worked as a Car Audio Install for years and my favorite was a brand new 1985 IROC-Z that the customer wanted us to build a sub cabinet for, (The cabinet we built for those was 12 pieces as we used every inch of the well). I went to start building and found the Amp that Best Buy installed was screwed to the front side of the well in the back. Was nervous to see how long the screws were and went to pull out the first screw and it was a 3-inch drywall screw that went right through the fuel tank and was wet with fuel. Sent him on his way back to Best Buy to have them replace the tank.

[edcmat-l1]

^^^ I've seen exactly that numerous times.

[blindsquirrel]

I've seen the stereo install drywall screw through a fuel line. No leaks until the screw was removed, somehow.

[TheMechanic]

I had a drywall screw used on an electric running boards that took out the rear electric windows only. That was a blast to find. Right up the body into the left channel that has the main wiring harness.

[blindsquirrel]

You never linked the address?? Ha!

I sent the shipping info in a PM, did you not get it????/

[TheMechanic]

It's not rich. It is oxygen deficient. During steady cruise the cat stores O2. On decel it releases it. I have some old scope screen shots of upstream vs downstream and you can watch it happen. I'll see if I can dig them up. Pretty sure there on one of my external hard drives.

Thanks. I would like to see that.