Testing Jeep O2, Oxygen sensors
- Thread starter Ecomike
- Start date
Dcoy1283
NAXJA Forum User
- Location
- Apollo, PA
Ok I have a question for the O2 sensor pros, I have a 2000 XJ, 4.0 auto and I have been trying to figure out a misfire issue and was instructed from another thread to check the grounds and volts to my upstream sensors (2). this is checking the harness side with the engine off I can see that I have 2 grounds as I should then when its running I have a wire with 13.89 volts, a wire with around 2 volts and my 2 ground I can see any where from .25 to .50 volts on them???? any thoughts???
- Location
- MilkyWay Galaxy
See post 31 and 32 for details on the 98 O2 sensor wiring, fuse, relay..... here:
http://www.naxja.org/forum/showthread.php?t=1094877
http://www.naxja.org/forum/showthread.php?t=1094877
What reader/program did you get? I have an iPhone and I'd like to get something like this.
- Location
- MilkyWay Galaxy
http://www.ebay.com/itm/ELM327-V1-5...to-Diagnostic-Interface-Scanner-/150802253413
http://www.ebay.com/sch/i.html?_trksid=p2047675.m570.l1311.R3&_nkw=obd-ii+usb&_sacat=0&_from=R40
http://www.squidoo.com/usb-obdii-laptop-diagnostic-cables-review
That should get you started. The aftermarket apps and software is the important thing. Some is free, some has a demo period, some is about $100 that does about everything but wash dishes, LOL.
lol
I've been looking at a few cheaper handheld scanners, $20-30 range. It seems like the blue tooth ones with smartphone apps have a LOT more in terms of data processing and abilities.
- Location
- MilkyWay Galaxy
Good info here on newer HO O2 sensor wire colors, O2 sensor...
http://www.naxja.org/forum/showpost.php?p=245828939&postcount=32
http://www.naxja.org/forum/showpost.php?p=245828939&postcount=32
Originally Posted by Lowrange2
Nice, those colors match the wiring I had last night.
I still only got 4.2 volts on the wire that should have 12 volts.
If you are looking for O2S heater power (12 VDC) at wire (Dark Green/White) of the body harness, don't forget that the engine has to be running inorder to activate the ASD relay, which powers the O2S heaters.
You may want to deatch the O2S connectors and move the body harness connector to the top siide of the engine bay to make it easier to work on. Start the engine, using your voltmeter, (+) probe to the body harness Dark Green/White wire pin socket and the (-) meter probe to the Black wire pin socket. You should see battery voltage (12 VDC +). If you are still getting 4.2 Volts, probe from the 12 Volt supply pin socket to the engine (ground). Still no 12 Volts? Shut the engine down and remove the battery negative post connector and using your Ohmmeter, read from the Black wire pin socket to the engine (ground). You should read continuity (less than .5 Ohms). No good? remove the ground wires at ground point G101 and clean each wire terminal end and reattach. Try for continuity again.
I'll check the fuse and track down the issue.
I still never got direct continuity to ground in any of the wires.
You should have continuity from the body harness Black wire pin socket to the engine (ground), see above. You probably won't see continuity from body harness wire Brown Yellow pin socket to ground, that's the O2S return (ground) in the PCM, unless you disconnect the appropriate PCM connector and read from pin to pin in this circuit.
I need to verify 12 volts to the Dark Green/white wire
and ground on the black wire.
blistovmhz
NAXJA Forum User
- Location
- Vancouver, BC
Re: Testing Jeep O2, Oxygen sensors RENIX Manual is right
Hey EcoMike. You helped me troubleshoot my '90 XJ years ago and thought I'd shoot this by you.
New Jeep is a 98XJ, and just started noticing O2 issues with it as well.
Heater power is 13.7V, both grounds are good, and the sensor lead is betwee 0.1 and 0.9V, but it's not flapping around like I'd expect. Seems to hang at 0.8 for a while, then drop down to 0.1 and hang out for at least a few seconds. Doesn't seem to be a pattern, and it hangs for a different amount of time at either end. I noticed this on my OBDii tool a while ago but wrote it off as an application issue rather than a reflection of real world data.
Incidentally, my mileage has recently plummeted from 21mpg to around 15-16 on the highway (33" 6.5"lift).
I had the exhaust downpipe off to bang out that dent above the axle, and I'm beginning to wonder if it's really supposed to be there from factory (as has been suggested by a few people) to increase backpressure slightly for the o2 sensor to work properly. Any idea on this?
Hey EcoMike. You helped me troubleshoot my '90 XJ years ago and thought I'd shoot this by you.
New Jeep is a 98XJ, and just started noticing O2 issues with it as well.
Heater power is 13.7V, both grounds are good, and the sensor lead is betwee 0.1 and 0.9V, but it's not flapping around like I'd expect. Seems to hang at 0.8 for a while, then drop down to 0.1 and hang out for at least a few seconds. Doesn't seem to be a pattern, and it hangs for a different amount of time at either end. I noticed this on my OBDii tool a while ago but wrote it off as an application issue rather than a reflection of real world data.
Incidentally, my mileage has recently plummeted from 21mpg to around 15-16 on the highway (33" 6.5"lift).
I had the exhaust downpipe off to bang out that dent above the axle, and I'm beginning to wonder if it's really supposed to be there from factory (as has been suggested by a few people) to increase backpressure slightly for the o2 sensor to work properly. Any idea on this?
- Location
- MilkyWay Galaxy
O2 sensor could be on its last legs, intermittent, Fuel injector, spark plug, or spark supply could be failing, intermittent, or it could be what you suggested on the exhaust MOD, and or you might have created a small exhaust leak doing the exhaust pipe Mod or some combination.
Also the Cat could be plugging up or broken causing intermittent back pressure....
When did the fuel MPG drop, before or after the work on the exhaust?
Also the Cat could be plugging up or broken causing intermittent back pressure....
When did the fuel MPG drop, before or after the work on the exhaust?
- Location
- MilkyWay Galaxy
I think the exhaust dent is factory.... Did you replace the donut seal and make sure the threads were good, and that you got a good seal at the flange?
blistovmhz
NAXJA Forum User
- Location
- Vancouver, BC
Okay, so I took off the downpipe to "fix" that dent and the next day I had to go do my vehicle emissions test. Failed miserably with extremely high NOx and slightly high HC/HO.
Back in the garage, I replaced both O2 sensors, made sure my exhaust was sealed, and somehow decided I thought I had a leak between my #6 cylinder and the rear water jacket, so I pulled the head, cleaned up the chamber/valves/everything, threw in a new head gasket, and while I was at it I threw on my new exhaust header and new RAD.
Some time between fixing the exhaust dent, and doing everything else, MPG and power dropped by around 20-30%. The cylinder leak seemed to be real as I was blowing exhaust into the rad. Not doing it anymore, so I figure I wasn't wrong.
I checked the O2 with an analog multimeter, but the only one I can find has minimum increments of 5V and it's really difficult to see if it's flapping around correctly. According to my OBDii interface, the upstream O2 isn't flapping very often, and that's what it looked like on the multimeter as well. Swapped back my old O2 sensor and get the same response. Tried a third just cause, and same deal.
So, assuming I'm reading the O2 correctly, what would cause it to have a slow response? Vac leak might do this? Or as a few guys have hinted at before, maybe hammering out that exhaust dent really did cool down the exhaust stream and now my O2 isn't working properly? Or, as you suggested, maybe an exhaust leak? (it'd have to be a pinhole cause I can't find it.)
- Location
- MilkyWay Galaxy
If the 98 has precats in front of the front O2 sensors they may have been damaged some if coolant got to them.
Check the HEGO fuse, that powers the heaters again in the O2 sensors.
The analog meter must be at least 20,000 ohm impedance or the meter screws up the reading, and the sensor must connected to the PCM/wiring, so you must back probe the connect with a good probe-contact to get good reliable readings.
Sounds like the engine was running too lean, which could have damaged the rear cat converters. Does the engine bog down on acceleration or high rpms?
I am not the expert here on the 98s, so maybe others will post up. Might also check for damaged wires to the O2 sensor, road hazard, contact with hot parts could have damaged the sensor wires to the PCM
Check the HEGO fuse, that powers the heaters again in the O2 sensors.
The analog meter must be at least 20,000 ohm impedance or the meter screws up the reading, and the sensor must connected to the PCM/wiring, so you must back probe the connect with a good probe-contact to get good reliable readings.
Sounds like the engine was running too lean, which could have damaged the rear cat converters. Does the engine bog down on acceleration or high rpms?
I am not the expert here on the 98s, so maybe others will post up. Might also check for damaged wires to the O2 sensor, road hazard, contact with hot parts could have damaged the sensor wires to the PCM
- Location
- Rainy side of Washington
Ecomike is probably on the right track, but I just want to clarify that 98s don't have precats. Only 01s and CA emissions spec 00s have them.
Also, I am 99% sure that on HO XJs/MJs, the same fuse (it's a blue 15 amp one, iirc) powers the ECU, both O2 heaters, the alt field coil, all the injectors, the fuel pump, and the ignition coil. Because for a while I had a wiring issue on my 96 (shorting out downstream O2 heater wire) that would blow that fuse and leave me dead in the water, and my 98 did the same exact thing when the fuel pump wiring got shorted as well as when the O2 wiring got smashed a few years back. I'm not 100% on that exact list of things powered by that fuse, but it's definitely accurate with regards to the ECU, O2 heaters, and fuel pump, because they sure shut it off in a hurry when the O2 heaters/fuel pump wiring shorted out :laugh2:
Also, I am 99% sure that on HO XJs/MJs, the same fuse (it's a blue 15 amp one, iirc) powers the ECU, both O2 heaters, the alt field coil, all the injectors, the fuel pump, and the ignition coil. Because for a while I had a wiring issue on my 96 (shorting out downstream O2 heater wire) that would blow that fuse and leave me dead in the water, and my 98 did the same exact thing when the fuel pump wiring got shorted as well as when the O2 wiring got smashed a few years back. I'm not 100% on that exact list of things powered by that fuse, but it's definitely accurate with regards to the ECU, O2 heaters, and fuel pump, because they sure shut it off in a hurry when the O2 heaters/fuel pump wiring shorted out :laugh2:
photondisruptor
NAXJA Forum User
- Location
- Redmond, WA
I just diagnosed a faulty sensor on my 1990 Renix with a 3-pin weatherpack adapter I made. It's basically about 6" of wire with male and female connectors on either side, and extra leads about 2' long crimped in for a good secure connection.
I hooked up my DMM and measured the sensor heater resistance at 50kOhm (dead). I then hooked it to the ECU and measured about 14V from the heater relay, and 5V from the ECU.
When I started up the engine, nothing changed, it ran rough, and the sensor indicated a solid 5V "signal".
I popped in a brand new Bosch 12009 and repeated the tests, and the heater voltage dropped to about 12.5, which meant it was actually working. The sensor voltage provided a solid tick-tock after only about 8 seconds of warming up.
I made this video to show what it looks like on my DMM:
https://www.youtube.com/watch?v=OchhM-F5UiM
I hooked up my DMM and measured the sensor heater resistance at 50kOhm (dead). I then hooked it to the ECU and measured about 14V from the heater relay, and 5V from the ECU.
When I started up the engine, nothing changed, it ran rough, and the sensor indicated a solid 5V "signal".
I popped in a brand new Bosch 12009 and repeated the tests, and the heater voltage dropped to about 12.5, which meant it was actually working. The sensor voltage provided a solid tick-tock after only about 8 seconds of warming up.
I made this video to show what it looks like on my DMM:
https://www.youtube.com/watch?v=OchhM-F5UiM
- Location
- MilkyWay Galaxy
Nice update to my old thread. Just found it, thanks. I was ill and off line most of that year. Be cool if someone did a youtube renix analog meter testing how to story some day. You tube has saved me some much time the last year working on the Ford and the Saturn...and doing my first ball joints this year on an XJ. Many people seem to follow how tos better with video. I do better with text in most cases, but video does show the exact parts and locations etc.
- Location
- MilkyWay Galaxy
How interesting and bizarre, Crazy that by the HO period they would shove all of those on one fuse, sounds more like an AMC save pennies standard than a more modern Chrysler standard. My 2001 Saturn has 2 ECU/PCM fuses in two locations (dash and under the hood as I recall, a PCM-A and a PCM-B) just for the PCM.
On the 87 Wagoneer XJ I have, the only facotory fuse on the O2 heater power is a huge fuse link near the battery that I smoked in the middle of no where one day when it got too close the exhaust manifold (my prior friend-mechanic routed it wrong when he installed the new one ages ago). My voltage dropped way deep into the red, AC died, and finally smoked from under the hood. I pulled the O2 heater relay that was still working and drove the last 200 miles home with no problems.
On the 87 Wagoneer XJ I have, the only facotory fuse on the O2 heater power is a huge fuse link near the battery that I smoked in the middle of no where one day when it got too close the exhaust manifold (my prior friend-mechanic routed it wrong when he installed the new one ages ago). My voltage dropped way deep into the red, AC died, and finally smoked from under the hood. I pulled the O2 heater relay that was still working and drove the last 200 miles home with no problems.
- Location
- MilkyWay Galaxy
I am revisiting this subject as my Renix rig is switching from closed loop to open when It stumbles in a miss fire I am troubleshooting. When it goes to and parks in open loop for 1-2 minutes at idle before finally going back to closed loop, my Snap-on MT-2500 reads about 0.68 Volts, low volts, and claims the engine is running lean.
But one of my last posts here seems to contradict this, and to make matters worse, the Snap-on MT-2500 manual says the opposite of what the scanner says, LOL, it says low volts is rich???. Whose on first and whats on second.
HTh do we nail this down once and for all???
But one of my last posts here seems to contradict this, and to make matters worse, the Snap-on MT-2500 manual says the opposite of what the scanner says, LOL, it says low volts is rich???. Whose on first and whats on second.
HTh do we nail this down once and for all???
Last edited:
- Location
- MilkyWay Galaxy
Re: Testing Jeep O2, Oxygen sensors RENIX Manual is right
Is it possible that the Renix O2 sensor high voltage, 5V versus low voltage down to 0.x volts lean/rich is the opposite from the HO 0-1 volt sensors?
And that is what has caused much of the manual confusion over the years?
Am no longer sure which is right for Renix. My Snap-on MT-2500 says low voltage on Renix is LEAN, but the manual that comes with it says low voltage on Renix is rich. Mine is running low voltage in open loop which should be rich unless something is wrong, and mine has a miss when I give it gas, so something is wrong, but at idle for 1-2 minutes it goes back to closed loop, so the O2 sensor works. I am tracking down injector, or cylinder or plug issues causing the stumble on revving.
Is it possible that the Renix O2 sensor high voltage, 5V versus low voltage down to 0.x volts lean/rich is the opposite from the HO 0-1 volt sensors?
And that is what has caused much of the manual confusion over the years?
Am no longer sure which is right for Renix. My Snap-on MT-2500 says low voltage on Renix is LEAN, but the manual that comes with it says low voltage on Renix is rich. Mine is running low voltage in open loop which should be rich unless something is wrong, and mine has a miss when I give it gas, so something is wrong, but at idle for 1-2 minutes it goes back to closed loop, so the O2 sensor works. I am tracking down injector, or cylinder or plug issues causing the stumble on revving.
It has been mentioned in other threads that the RENIX version how o2 content is measured is a little different than you would expect. It is pretty confusing and totally counter-intuitive.
From the RENIX manual
"When the oxygen content is low, (rich mixture), the voltage signal will be less than 2.5 volts. A lean mixture (high oxygen content) the voltage is signal is above 2.5 volts."
So
1 volt = rich
5 volts = lean
2.5 just right....
(more o2= lean mixture = lower resistance = higher voltage ???)
From wikipedia which quotes other references so it must be true. :sunshine:
"So, for fuel-rich exhaust (lower oxygen concentration) the resistance is low, and for fuel-lean exhaust (higher oxygen concentration) the resistance is high."
(more o2= lean mixture = higher resistance = lower voltage )
Another reference
http://www.hybridconversions.com/v/vspfiles/assets/images/oxygen sensors explained.pdf
As titania is an N-type semiconductor with a structure TiO2-x, the x defects in the crystal lattice conduct the charge. So, for fuel-rich exhaust the resistance is low, and for fuel-lean exhaust the resistance is high.
(more o2= lean mixture = more resistance = lower voltage) same language that wikipedia uses)
(more o2= lean mixture = higher resistance = lower voltage )
Anyway I spent some time on this today and I think I can confirm that the RENIX ECU will see high voltage as rich and low as lean. I had a bad fuel pressure regulator and it caused the o2 sensor to read less than 1 volt consistently at idle. This drove me crazy and I am hoping this research helps others that are struggling with the same troubleshooting dilemma. If you have a RENIX sensor that consistently reads less than 1 v after warmup something is causing it to run rich and it is likely to be the fuel pressure regulator. It means the o2 sensor is functioning properly.
Think that this is confusing because you have multiple reverse logic things happening.
Higher resistance = lower voltage higher o2= less resistance = higher voltage... arghh!!!
So I smelled a rat and decided to read the bloody patent. Which I have linked to and list the relevant excerpt below. It would appear that Titania sensor's resistance actually decreases with the amount of o2 in the stream. It is an inverse relationship....
(more o2= lean mixture = lower resistance = higher voltage )
I am going to challenge Wikipedia on this unless anyone sees what I am sure I am missing. :bs:
http://www.google.com/patents?id=pF...AA#v=onepage&q=Patent number: 5111792&f=false
!!!1 Done.
