Is there a correct way to read the voltage coming out of the downstream sensor engine side connector pins to see if it's getting voltage?

the sensor generates the voltage. it is fed the sensor ground from the PCM. the only voltage it gets is 12v heater.

some scanners cant accurately sample the o2s. sample rate is too slow to catch peak to peak. you may be only catching the lows. you are correct that the voltage shouldn't be over 1 v. nominal output is .5v so it should cycle from 0 to 1.

Try checking sensors on bench. i checked mine this way. It may not be a scientific as it needs to be, but in your case it would probably answer your question.

Testing O2 sensors on the workbench (borrowed this from http://mr2.com/TEXT/O2_Sensor.html)

Use a high impedence DC voltmeter .

Clamp the sensor in a vice, or use a plier or vice-grip to hold it.

Clamp your negative voltmeter lead to the case, and the positive to the output wire.

Use a propane torch set to high and the inner blue flame tip to heat the fluted or perforated area of the sensor.

You should see a DC voltage of at least 0.6 within 20 seconds.

If not, most likely cause is open circuit internally or lead fouling.

If OK so far, remove from flame. You should see a drop to under 0.1 volt within 4 seconds.

If not likely silicone fouled.

If still OK, heat for two full minutes and watch for drops in voltage.

Sometimes, the internal connections will open up under heat.

This is the same a loose wire and is a failure. If the sensor is OK at this point, and will switch from high to low quickly as you move the flame, the sensor is good.

Bear in mind that good or bad is relative, with port fuel injection needing faster information than carbureted systems.

ANY O2 sensor that will generate 0.9 volts or more when heated, show 0.1 volts or less within one second of flame removal, AND pass the two minute heat test is good regardless of age.

When replacing a sensor, don't miss the opportunity to use the test above on the replacement.

This will calibrate your evaluation skills and save you money in the future.

There is almost always *no* benefit in replacing an oxygen sensor that will pass the test in the first line of this paragraph.

PS, dont burn your finger... dont ask why i caution you...

 

Always learning from ya'll!

 

From the article i linked

"Undercoating, antifreeze or oil on the *outside* surface of the sensor can kill it."

rut roh

 

Thanks for the great info Zee, appreciate it!

I remember bench testing one of my o2 sensors before with a torch but of course forgot the exact procedure. I just hope I can remove the sensor since it's rusted in pretty good thanks to the salt/heat. Have been putting rust cutter on it though since yesterday. Know it's easier if the exhaust is hot but may just carefully heat around it with a torch.

Rut roh is right, I too read about the oils and such killing a sensor! That's what I get for spraying 5 cans of Fluidfilm (sheep/wool lanolin type oil + wax) on the underneath when 34 degrees in the dark. Hope that's not the problem but I'll let you know how the test goes.

BTW, am I reading that diagram/schematic right in that the black/orange wire is the output to the PCM you connect the the positive lead on the DC voltmeter to when bench testing? Believe it is in looking at the same schematic but a little different view.

 

i believe the grey wire mates up to the sensor input to the pcm. the two white wires are heater and the black is sensor ground.

the article I referenced speaks of one, two, and three wire sensors so you'll need to adapt the info to a four wire sensor. IIRC, i had to go to the black wire with black lead and grey wire with red lead. double check me on this.

be sure not to ohm through the sensor.

you may want to try back pinning it like it says in the article, but once again, the sampling rate on the meter may not be fast enough to monitor the crossing from rich to lean. adding propane or air to the mixture while it's running is pretty much fool proof. Sample rates wouldnt matter much in that situation because it will go high or low and stay there.

 

Geeze, I must be having brain lapse since was talking about the wire color codes on the connector w/4 wires going to the PCM rather than the connector going to the o2 sensor itself.

Regardless, I took the connector to the new NTK 23121 sensor I have and plugged it slightly into the connector to the o2 sensor still installed. I had pulled the sensor connector up up to the top of the engine compartment which made it easier to clean.

When holding the locking tab up on the new NTK sensor connector it appears it connects to the connector leading under the injector harness plastic shield/cover as follows. (cross referenced on the last schematic posted)
- top/left white connects to Black/tan (heater wire leading to rear downstream sensor),
- top/right white connects to dark green/orange (also a heater wire going to downstream sensor),
- bottom/left black connects to black/orange (leading to A24 of PCM, sensor signal)
- bottom/right gray connects to black/light blue (sensor ground to A4 of PCM)

I'll double check this when testing to make sure it's correct.

The only thing I used ohm on using my meter were the 2 white heater wire cavities on the sensor connector. Per FSM (p.14-49) spec is supposed to be 5-7 ohms across the white wire leads and mine read 5 ohms. I tested it early this morning so the heater supposedly is ok.

BTW, if I didn't ruint the sensor spraying fluidfilm on it wouldn't doubt I ruint spraying acetone/atf mix along with PB on it. It was in a hard place to spray on just the thread and I was pretty sloppy with it not knowing it shouldn't have anything like this on the outside.

 

I was pretty sloppy with it not knowing it shouldn't have anything like this on the outside.

i had forgotten that the sensor somehow samples the outside air. I had yhat figured out when i was messing with mine a few years ago... but that was a few years ago...

 

I've read something about anti-seize, like if the sensor has a bright plating, no anti-seize required, else it lubricates the threads and allows you to over-torque it leading to possible thread damage. OK with dull grey plating though (unplated steel?)

ps: found an NTK faq, here:
http://ngkntk.co.uk/index.php/technical-centre/lambda-sensors/notes-on-installation/

It says, dont use anything since everything is pre-applied at the factory.

 

i think that little hole in the back is the outside o2 level sniffer or maybe it comes in around the wires? i forget...

 

Yeah the O2 sensors have a permeable membrane that compares the oxygen content of the exhaust to the outside air. There are little holes usually near where the wires enter the housing. That's why when you add a sensor to an existing exhaust you are supposed to install it only within certain angles to avoid moisture buildup in the sensor.

http://wbo2.com/lsu/lsuinstal.pdf

 

Actually Zee what looks like a black hole on the side of sensor in my pic is actually a black mark made by an ink marker and I should have explained that with the photos. The end tip looks like it's been heated before so bet the black mark just means it's been tested to keep track of it w/the untested sensors.

By gosh Josh you are correct in there are 4 small holes towards the top of the sensor! I couldn't really see them w/o looking close since there's white ceramic, or maybe that's the membrane you speak of, right inside the holes (see below photo w/red arrows pointing towards the holes).

I had thought maybe the outside air was pulled in where the wires go in the very top but there's a rubber grommet the wires go through which must seal the sensor. I'm glad the outside air isn't pulled in the very top since I have to put corrugated plastic tubing electrical taped onto the top of the O2 sensors, along with all my other wiring/tubes/hoses, to keep he bushy-tailed rats and other rodents from eating through them.

 

Actually Zee what looks like a black hole on the side of sensor in my pic is actually a black mark made by an ink marker

that's a black mark on my record. wah wah wah waaaaaaah :droolie:

 

I don't think I've ever had such a difficult time removing an upstream O2 sensor and it was like it was welded in the downpipe! If I wouldn't have bought a full-size torch kit last year I don't think it would have come out and surely would have snapped it off or broken the threaded welded bung out of the pipe itself.

I heated the bung up red hot with a brazing tip and as soon as cooled ever so slightly the sensor locked in again. This was only with 1/2 turn out so I must have heated the bung up red hot 6-8 times and the sensor felt like it was ready to snap anytime. A deep well slotted oxygen sensor socket may have helped but still bet it would have locked back in real quick as it cooled quickly.

My plan was to bench-test the old NTK 56028603 sensor I installed many years ago but forget that since I destroyed the sensor in removing it. Besides I saw this sensor read .000 on my scanner again once it warmed up so figured it must be bad. I started rounding off the nut corners on the sensor w/an open-end wrench and had no choice but to cut the wires off right at the sensor while putting a 7/8" deep-well impact socket on it with a 1/2 drive ratchet. Still took a whole lot of heat applied to turn the bung red and it felt like threads were really messed up.

Sure enough once the sensor was removed the bottom couple threads were gone/stripped. The bung threads didn't look too bad although they were super rusted. I used a battery terminal cleaner in the bung threads, twisted the heck out of it, and also used a small wire brush on the outside of the bung where the sensor washer meets.

Then I applied some O2 sensor-safe antiseize on the bung threads and the new NTK 23121 sensor already had it on the threads from the factory as previously mentioned. Once the new sensor was in about 1/2 way it stopped/seized. I tried going back/forth a little more and finally removed it since it wasn't going in any further. Sure enough I started flattening the the first couple thread on the new sensor, this wasn't going to work, and tried straightening up the threads some with a small file.

Figured I was going to have to tap those bung threads, came in from the dark/cold, and found the answer here in a forum search; a sensor thread chaser. Called the local parts stores and had to run to the nearest one to pick an "OEM 25255 Oxygen Sensor Thread Chaser" for $10 which is M18x1.5 while fitting 18mm spark plug holes too. Also pickup up a $10 deep-well slotted 7/8" sensor socket.

It says to use lubricant on the thread chaser directions but didn't want to use something which would contaminate the new sensor so used antiseize. Those bung threads were so rusted it almost felt like I was cutting new threads but it cleaned them up real good. Used a paper towel and my little finger to remove the excess antiseize/rust/metal including on the inner part of the pipe which is near the sensor tip.

I really didn't like the way the cheap deep-well slotted sensor socket bent the wires at such a right-hand angle at the top of the sensor and it's almost like it isn't deep enough. Plus I couldn't really feel the threads using it so installed the new sensor with my MAC 7/8" open-end wrench. It still felt a little wonky towards the end, sure didn't want to strip the threads on the $35 sensor, but believe I have about 30 ftlbs spec of torque on it.

Once I fired the engine there was quite a bit of smoke coming from the sensor/bung area and wondered if I had it tight enough? Turned out there were no leaks but the excess antiseize was burning off/almost dripping as it burned. Sure hope it wasn't doing that on the inside towards the tip.

The new NTK upstream sensor must have fixed my problems since my scanner readings were a whole lot better w/no codes thrown. STFT was 3.9 instead of 33.9, S11 upstream readings were .12-.74 although .12 may have been open loop, S12 downstream read .2-.72.

One thing I can't figure out is why the downstream/cat sensor was reading 1.000-1.120, which may indicate it's bad, but once the engine warmed up it reads correctly? Also on my scanner why does it read, "Catalyst Mon = inc" which I assume means incomplete? Thanks for any help/input!

Geez, can I make this novel/thread any longer?? Yep, Lol!

I took some photos of the new sensor connected to the sensor wire harness connector for those having a difficult time reading schematics and figuring out color codes matches with a NTK sensor. While I posted the below info earlier it's been revised with additional info.

With locking tab up:
- Sensor top/left white connects to black/tan: heater wire tied into rear downstream sensor bk/tan wire, heater ground strap (G105, 8W-15-3).
- Sensor top/right white connects to dark green/orange, also a heater wire tied into downstream sensor dkgrn/orange, connects to ASD relay.
With locking tab down:
- Sensor top/left black connects to black/orange, leading to A24 of PCM, sensor signal.
- Sensor top/right gray tied into black/light blue of rear downstream sensor,ground to A4 of PCM

So while running if back-probing the sensor/wiring harness connector for voltage with a meter set to DC the black lead/probe on the meter should be on the gray ground wire on the sensor side or black/light blue on the harness side since this is ground. You can also just ground the meter black lead/probe to the block. The red lead/probe should be connected to the black wire on the sensor side or black/orange wire on the harness side since this is the sensor signal connection.

You may want to go back to ZeeJay's link earlier in this thread for testing for voltage with the sensor installed. With engine fully warmed voltage should be more than .7V, changing rapidly to less than .2V, and not staying around the middle .45V for a good sensor (from the link).

Here's the photos showing the sensor/harness connectors attached and my old destroyed sensor. Notice the black carbon from where it was running bad/throwing codes and don't know what the deal is from all that white corrosion near the base?

I had to throw in a pic of my newfie Charlie w/the sensor. What a companion and he always lays in the grass watching my every move since we rescued him 5 years ago. He hates the flash of cameras as can probably seen in his eyes! Lol!

Sorry for the length but figure if someone has the patience to read through this then it may help them with O2 sensor problems.

 

The reason the O2 monitors are incomplete is cause you need to drive the jeep for several miles to let the internal emissions tests complete. This is a safeguard to trying to hide problems when a vehicle is being inspected.

Take it out on the highway or county road, bring it up to 55 mph or higher for a good 6 to 10 miles then recheck with your scan tool, it should show the tests as complete, or alternatively you will have the MIL illuminated once again.....

 

Thanks for the info Smokey1r and wasn't aware you need to drive it for the cat monitor to be ok/complete.

Nice of me to use the wife as a guinea pig and told her to drive it to/from work on her 50-mile round-trip today. Even though they showed a big traffic jam on the freeway she'll get it up around 65mph part of the trip and at least she must have made it there since I didn't receive a call. I'll recheck it as soon as she gets home and thanks again for the info!

 

I didn't want to lengthen my previous post w/photos any longer than it already was. Should mention after installing the new upstream NTK sensor I was curious how my cat was performing, along with the sensors, so used the below test in the video. Not sure who originally posted this video and maybe it was coralman or another member?

I had bought a "General IRT207 Infrared Thermometer" a few months ago to use in unison with my Actron scanner/reader just for this purpose.

I brought my 96 4.0 up to normal operating temperatures where it was reading 200F on the coolant and 100F on the IAC. Then I used a board between the gas pedal and seat so the engine would hold at 2,000rpm. In checking the cat temp it read between 300-310F on the front inlet weld and around 395-412F on the outlet metal. This is exactly what you want where there is about a 100 degree difference between front/rear cat temps with the front being on the cooler side. In other words the cat is internally burning up the N02/emission gases so it should be much hotter at the rear.

The o2 sensor readings were a little more vague. The upstream voltage read anywhere from .4 to .74 and the downstream sensor was reading .2 to .72. Believe the rear one should be holding a little more steady and it was jumping around quite a bit at .2,.3,.46, .5 & .72 but holding at .46+ more than the lower voltage numbers. Fuel trim was good at 3.9 as mentioned earlier.

At least the engine seems to be running good although those 703 injectors I put in new about a year ago sure click a bunch.

Here's the video and sorry he used foreign cars instead of Jeeps! If you just want to see the o2 sensor readings/cat temp test go to 4:45 in the video.

 

Uni, I thought i had you straightened out on that drive cycle business,

read this again!

 

Holly cow Zee, great memory and find! You expect me to remember all that stuff 1 year 8 months later?? LOL! I really do appreciate you coming to my aid on numerous occasions!

I did read through a lot of that again and must be dense! About 1/2 hour after my wife drove 25 miles home from work I threw my scanner on it. The oxygen sensor monitor was complete but the cat monitor was incomplete. So I guess once you turn the key off you have to go through the drive cycle again, at least to complete the cat monitor? And what is monitoring the cat to begin with; the downstream o2 sensor?

The readings looked pretty good, with no codes, but the downstream o2 sensor was still jumping up to 1.04-1.06 once in a while. Of course once it warmed up it didn't do this hardly at all but readings were all over the board. Guess the best thing to do is go through the drive cycle and then back probe the connector with it running to see what I find.

I'm beginning to wonder now if one bad o2 sensor can kill the other? In other words when it was running so bad (1 day) with the bad front/upstream o2 sensor when I pulled that sensor it was completely covered with carbon. I wouldn't doubt the rear/downstream one looks the same way unless the cat burned some of the carbon up/off?

I try not to think about it but know the o2 sensors and cat went through a period of having a cracked manifold and then a vacuum leak on the intake about a year ago. Know Zee remembers that well too since he had the same.

 

I kept having the same code, id look with my scan tool and the readings were borderline id clear it and a few months later it came back. I also noticed the O2 sensor tests were always incomplete no matter how many times the jeep was used and left it to idle etc..
So with the muffler grenading one day while having to accelerate hard on the highway on ramp to avoid an idiot trucker that had a clear left lane and refused to yield i decided to retrofit the exhaust system, new cat, muffler and both up and downstream sensors, after that i started over with all the monitor tests and before i knew it all the tests were completed!.
So if you have aging or contaminated sensor it might not allow the test to complete.
So far since the retrofit Ive only had the same cat efficiency code get spit out once, i extinguished it and it has yet to come back, just a strange fluke?

Its not exactly good on the wallet sometimes but its very wise to replace the O2 sensors in sets..... yes i did use NTK up and down stream sensors purchased off of rockauto.com .... the same sensors at the local idiot zone were double in price!!! :rofl:

 

just had to poke a little. there was no memory involved, just find. as i said before, I have to post on here to remember what I've done.

for me , the catalyst monitor is tricky to set. those conditions just dont happen unless you're trying... in Alabama anyhow.

"Drive with a steady vehicle speed between 30 and 45 mph for 2 minutes.". Try to do that. you need a long flat stretch of road with no traffic.

Mine will not set unless i either hold the pedal still or set the cruise at 40 on flat ground. You know my setup and the light doesnt come on because the monitor is not set. i can intentionally drive the cycle and boom... CEL

 

I just went back and read that whole thread again. I was waay over my head since had just bought my Actron 9575 scanner and was overwhelmed with all the info. Believe that thread deserves some closure.

http://www.jeepforum.com/forum/f13/pcm-doesnt-hold-save-codes-1332105/index4.html#post18209730

Right around the corner of my rural road there's a nice flat stretch of highway with little traffic and I'll see if I can reset the catayist monitor while driving with the scanner connected.

Hate to say it but I ordered another downstream NTK 23016 sensor for it yesterday through ebay since I'm seeing readings above 1.000 on the current one. I fantasized it was Cyber Monday so all electronics are on sale! Lol, not really, although $35 w/free shipping isn't too bad. I'll still try testing the current one first to make sure it's bad or the readings aren't within spec.

That video I posted on checking the cat performance may be good in theory but would have been nice if he would have mentioned what kind of readings/temps you would see if clogged? I shouldn't even bring that up since I paid a welder $35 to tig-weld SS wire between the cat/muffler on an exhaust which is only about a year old. I have my own mig-welder now but sure haven't practiced much on thin exhaust.

While my ZJ runs smoothly it just doesn't have any power in getting up to speed. Just bought a compression tester which is my next move.

 

Eric has a video somewhere comparing a clogged/bad converter to a normal operating one using his IR gun, I watch his videos all the time. :laugh: Also check out Scotty Kilmers YouTube channel, he has similar videos to Eric's in all aspects. I have the same scanner as you, it's a very nice unit.

Here's a video from Eric to check for exhaust restrictions.

Here's a video from Scotty testing his converter.

P.S. Your mammal is adorable.

 

Eric has a video somewhere comparing a clogged/bad converter to a normal operating one using his IR gun, I watch his videos all the time. :laugh: Also check out Scotty Kilmers YouTube channel, he has similar videos to Eric's in all aspects. I have the same scanner as you, it's a very nice unit.

Here's a video from Eric to check for exhaust restrictions.

Here's a video from Scotty testing his converter.

P.S. Your mammal is adorable.

Yeah Jason, that Actron CP9575 scanner is hard to beat for $100 and don't know how I went w/o one for so long! It opened up a whole other world what was actually going on.

Thanks for the videos in checking a cat and real interesting. It's too bad there's so many different types of test gauges for checking/testing different things. I could probably use a vacuum gauge anyhow but bet I could somehow connect/adapt my Motive brake power bleeder to the intake since it has a vacuum gauge on the tank.

If I went to the extreme of drilling holes in the front/back of the cat it would be nice if I could somehow adapt my compression tester to the exhaust by removing the rubber tip but don't know if it would work in reading exhaust pressure. Wonder where Scotty picked up those 1/4" metal plugs?

Charlie thanks you for the compliment, the sweetest dispositioned dog I have ever owned, and just like a big 120lb teddy bear! His dad went 185 lbs, mom weighed 155, but his growth was stunted by keeping him in a cage w/o enough food/exercise from the twit who owned him the first year. Our family is so glad we rescued/adopted him as I'm sure he is too!

Ya might want to also consider the timing chain being worn or stretched, when i did the partial exhaust retrofit it did increase my gas mileage, had some power gains but nothing like i expected. When i had to service the water pump months later i also had to contend with the infamous timing chain cover gasket leaking coolant, so i decided to go the full mile so to speak and replaced the timing chain and sprockets while i was in there. After that the jeep has balls once again i was taken by surprise how much power it had once again expecting the usual lackluster performance.

Thanks for the input Smokey and I've often wondered if my timing may be off but haven't thought the timing chain may be stretched. I've often thought about taking it in to the local shop to have the timing checked while also smoking the intake to make sure I don't have any leaks. But in checking the intake/hoses with starting fluid/propane I've yet to see the rpm's go up which would indicate a vacuum leak.

With 205K on the clock the timing could be off and installed a new Remy distributor in the engine about a year ago. Made sure it went right back in the same as the old one came out. Luckily I haven't had coolant leaking out from the timing chain cover, knock on wood, but agree it would be a good time to check the timing chain/gear when off.

Thought it was strange the other day when checking the o2 sensors I removed the rubber cap off of the unused large plastic nipple on the engine-side/top of the airbox and stuck my unlit propane torch nozzle in the nipple. Even with the propane turned to high my engine rpm's never did increase and guess you need to feed it in somehow directly to the intake??

Coralman, yeah agree it's like a Sun thread and sorry for helping make it so long! ;-)

 

Ya might want to also consider the timing chain being worn or stretched, when i did the partial exhaust retrofit it did increase my gas mileage, had some power gains but nothing like i expected. When i had to service the water pump months later i also had to contend with the infamous timing chain cover gasket leaking coolant, so i decided to go the full mile so to speak and replaced the timing chain and sprockets while i was in there. After that the jeep has balls once again i was taken by surprise how much power it had once again expecting the usual lackluster performance.

 

Man, this is a Sunday thread,lol. It'll take me a quiet Sunday to sit and take this and Zee's attached stuff in at one whack

 

At 205k i can almost guarantee it needs to be changed out!!!! The chain is most likely stretched causing a physical retardation or lag in the valve timing. The ignition timing is governed by the crank position sensor so the computer takes into account the cam position too compensating the best it can but none the less there's also a slight physical lag in the distributor causing a slightly higher resistance in spark gaping forcing the coil to work harder under this unfavorable condition to try to assure a complete burn of the fuel air mixture. all this causes very lackluster power output especially under WOT or close to WOT load conditions ...... oh man my head hurts trying to translate this to my fingers lol!!! :facepalm:

If you choose to change out the timing chain/sprocket set, gaskets etc.. you also might want to consider if it hasn't been done or in part done the front main seal, replace or sleeve the harmonic balancer, change out the water pump etc.... but all this depends on your pocketbook and whats in it aside from coralman's dust mites! :rofl:

 

I know I need to do this, and was near on the horizon, until the heater core episode. Will get to it eventually.

 

I take contributions Smokey

 

Ill gladly dump my dust mites in to your wallet!!! :rofl: :rofl: :rofl:

 

Thats an idea, extermination service for ZJ owners!

 

I need this service. Just bought some Husky floor mats for the rear and cargo. Can't help myself. :drool: