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Testing Jeep O2, Oxygen sensors

"Ignition off o2 causes parasitic draw."

Can you explain? the O2 sensor is two resistors. one is a heater, the other a temp-variable resistor.

Parasitic draw? What and how are you testing????

Are the harness wires damaged????
 
Cannot explain o2 sensor resistors. All I know is that my battery was dead due to new o2 sensors. Never had dead battery before replacing o2 sensor so I assume the wire harness is fine.

Testing why battery was dead.

Battery is new, must be a parasitic draw on battery. Disconnect battery negative, key off, nothing on. Put volt meter on 10 amp setting, touch one lead to battery negative, other lead to battery negative terminal and read amps.

Almost 2 amp draw slowly dropping to .86 amps. Unplug o2 sensor and read voltmeter, 0.0 amp reading.

I tried a NTK from Pepboys. Was supposed to have been a direct replacement but looked nothing like the original I had, it caused a parasitic draw.

Also tried a Bosch from O'reilly's. Was also supposed to have been a direct replacement and it looked nothing like the original either, it too caused a parasitic draw.

Never had dead battery before replacing o2 sensor.

Why did I replace o2 sensor?

Going freeway speed engine stumbles. Get off freeway and drive city speed, engine stumbles and quits. Restart engine, pull over and sit 15 minutes. Begin driving, after 5 minutes engine stumbles. Pull over for another 15 minutes and begin driving, 5 minutes later engine stumble. Repeat this process over and over again till I get home.

I replace IAC and CPS. Take for drive and after getting warm engine stumbles. Replace o2 sensor. Take for another test drive, runs fine. Turn engine off, next day battery dead.
 
Randy, 99% sure the O2 sensor relay that powers the electric heater element in the sensor is stuck ON, and draining the battery. Change that replay and see if the power draw does not vanish. My compliments on your post, great detail of the story, made it easy to know what is wrong! Not sure if that image below is right, so check some others online or the FSM for the right location.
picture_php_pictureid_18907_jpg_a6419108be3f1555d840dfeed843fcb82f14aab8.gif
 
I would agree with Ecomike on this one.
 
Thanks all for caring enough to give your valuable input. I appreciate it more than you can know.

The image posted for the jeep relays is correct per the FSM for 90 jeep. I replaced the relay and still get the battery draw.

To give you more info on the o2 sensor I have currently, which is also parasitic.

Upon trying the part store sensors (NTK and Bosch), I connected my MT2500 and they both showed a constant 4.98v output. The current sensor I have now, which is an Autolit sensor, the voltage bounces from 0.14v - 0.16v

The Autolite sensor that I have now, because the part stores sensors drained my battery, I bought on ebay because it looked like my original sensor. (ceramic with black boot on end and holes in the end that went into the exhaust). That sensor is new, it was just an older part from either a parts store or a repair shop that went out of business. And looks like it is in perfect condition.

The ebay listing showed it to be Autolite 02024 Oxygen O2 Sensor For 1987-1990 Jeep Cherokee, wrangler, Comanche. The only difference was that the connector on the autolite was a (male), connector. Wires were Grey, black and yellow. Where as my original sensor had female connector with grey, black red wires.

Looking at the 87-90 cherokee FSM, it showed that the Autolite ebay sensor was for the 2.5 liter with the yellow wire going to ignition and the grey wire going to ECU and black to ground.

Where as the FSM showed my original 4.0 sensor as having the grey to ECU, red to relay and black to ground.

Because the ebay autolite had a male plug, I replaced the it with the female plug from my original sensor. Grey to grey, black to black and red to yellow. ( I soldered the connections).

Is it possible that the o2 sensor for the 2.5 liter behaves differently than the 4.0 liter sensor?
 
What I found today:
What ever it was that took out my o2 sensor, or fouled its function, also took out my A/C compressor clutch. Or one of the replacement o2 sensors killed the compressor clutch. All the relays test good.

Maybe the ECU is shot. Anyone know of a shop here in Arizona, Phoenix area, that knows how to diagnose Jeep Renix systems?

thanks again guy's.
 
I jumped my compressor clutch with jumper wires and the clutch is working, just not when turning on a/c from cab. So I'm thinking there is maybe a fuse or a short somewhere from trying to run the aftermarket o2 sensor or when maybe when I experienced the stalling which led me to it change out the o2.
 
Sounds like a damaged wiring harness, somewhere to me. Bad ECU Renix is supper rare, like <.01% failures in 30 years, and only failures I ever even heard of were blown injector ground diodes that kept a fuel injector from firing. I am not buying that the O2 sensor are bad, they are just completing the circuit of a failed/damaged wiring or ECU...

There should be no power at any of the four O2 sensor wires with the ignition switch off!!!!

Is the Ignition switch shorted in the off position, or the wires at the switch/connector???
 
The o2 sensor has 3 wires. But still there should be no power going to them with ignition off.

There has to be a short somewhere if the ECU is not suspect. Just have to figure out where somehow or another.

Thanks for your thoughts.
 
My first guess is the O2 heater power from the battery is stuck on, burned contacts welded closed? The spring return can not reopen the contacts

The o2 sensor has 3 wires. But still there should be no power going to them with ignition off.

There has to be a short somewhere if the ECU is not suspect. Just have to figure out where somehow or another.

Thanks for your thoughts.
 
Parts stores show my sensor, white body, black boot with grey, black, red wires. What they give me via the part number are actually zerconia sensors rather than the correct titania sensors. Thats why they were creating a parasitic draw, it was due to them creating their own voltage for the heater element.

Got a used titania sensor, parasitic draw gone. I think it is lazy though or partially worn out because im not getting a open/closed back and forth loop and my LTFT and STFT are always at 128... (0%).
 
Yah, I am not buying that theory. I bet the used sensor has an open circuit, burned out heater element in the Titania sensor, thus can not cause the parasitic draw. And thus not going closed loop... Did you try using a new Titania sensor then if the draw is there again, pull the O2 sensor relay and see if the power draw vanishes? My bet is that relay or the female socket contacts/wires are shorted across the contacts sending power to the heater wire of the O2 sensor even with the ignition off. If I am right there will be 12 volts at the O2 sensor orange wire even with the ignition switch off.

With the ignition switch off, you should be able to short all 3 wires at the O2 sensor and not have a power draw, as there should be no electrical connection between the sensor and the battery positive post to pull electrons out of the battery.

I read that the non Renix rigs in 86-? used the other sensor type, thus the reason they screwed up and gave you the wrong one I guess. Good catch!!!

Parts stores show my sensor, white body, black boot with grey, black, red wires. What they give me via the part number are actually zerconia sensors rather than the correct titania sensors. Thats why they were creating a parasitic draw, it was due to them creating their own voltage for the heater element.

Got a used titania sensor, parasitic draw gone. I think it is lazy though or partially worn out because im not getting a open/closed back and forth loop and my LTFT and STFT are always at 128... (0%).
 
My 1988 ate a brand-new NTK 23553 sensor in the ~7 months since I had last passed smog. Voltage just stopped fluctuating and it stayed open loop. It was one of those light-gold colored, bullet looking three-wires. Not sure why, my emissions numbers were very good last test (it was installed for the test), not running rich/no HG leaks etc as far as I know. No battery drain either, for that matter. I know 02s don't usually just die, so I'm not ruling out an issue somewhere else but I haven't seen any symptoms.

Out of curiosity, I replaced it with a spare 02 that I had laying around, the older style with a ceramic insulator (I think it was a BWM or ACDelco). It's been a couple of months now and the XJ has been very happy with it - system drops into closed loop in ~10seconds, ST/LT fuel trims are good and MPG is fine. I'm interested to see how long it holds out; I know current wisdom has usually been to use NTK.
 
MY current wisdom has always been to use the OEM brand Bosch on Renix. Bosch invented and patented the one that was made for Renix.

Cruiser54 swears by NTK, so I find your post very interesting.

NTK was the OEM brand for 91 and up, HOs.
 
It was interesting to note for me that right at the same time I was getting parasitic draw from the sensors my A/C clutch stopped engaging. Even after removing them.

I bought a bosch and Walker sensors that matched the one I had before all my troubles started, white body, perforations on tip, Hole in the end with a flat bar insided. Both caused parasitic draw.

I got 3 junk yard sensors from 88-89 renix jeeps. No parasitic draw from any of them. 2 of which I got no ohms reading. 3rd one got 3.7 ohms.

After installing the one with the 3.7 ohms reading, no parastic draw and A/C clutch now engages.

While engine is cold loop would switch open/closed, but only till it warmed up, then it stayed on open loop.

Parasitic draw is obviously caused by the sensors having a heating element. Have no idea as to why they affected my A/C clutch.
 
My 1988 ate a brand-new NTK 23553 sensor in the ~7 months since I had last passed smog. Voltage just stopped fluctuating and it stayed open loop. It was one of those light-gold colored, bullet looking three-wires. Not sure why, my emissions numbers were very good last test (it was installed for the test), not running rich/no HG leaks etc as far as I know. No battery drain either, for that matter. I know 02s don't usually just die, so I'm not ruling out an issue somewhere else but I haven't seen any symptoms.

Out of curiosity, I replaced it with a spare 02 that I had laying around, the older style with a ceramic insulator (I think it was a BWM or ACDelco). It's been a couple of months now and the XJ has been very happy with it - system drops into closed loop in ~10seconds, ST/LT fuel trims are good and MPG is fine. I'm interested to see how long it holds out; I know current wisdom has usually been to use NTK.


What were your fuel trims?
Did it loop open/closed back and forth on cold start?
Wish I could find a new o2 sensor that didn't have the pre-heating element.
 
What were your fuel trims?
Did it loop open/closed back and forth on cold start?
Wish I could find a new o2 sensor that didn't have the pre-heating element.

You could disable the O2 heater by pulling the relay. If it still gets 12-14 volts the female relay socket wiring area (or nearby wiring harness) has a short, by passing the relay.
 
It was interesting to note for me that right at the same time I was getting parasitic draw from the sensors my A/C clutch stopped engaging. Even after removing them.

I bought a bosch and Walker sensors that matched the one I had before all my troubles started, white body, perforations on tip, Hole in the end with a flat bar insided. Both caused parasitic draw.

I got 3 junk yard sensors from 88-89 renix jeeps. No parasitic draw from any of them. 2 of which I got no ohms reading. 3rd one got 3.7 ohms.

After installing the one with the 3.7 ohms reading, no parastic draw and A/C clutch now engages.

While engine is cold loop would switch open/closed, but only till it warmed up, then it stayed on open loop.

Parasitic draw is obviously caused by the sensors having a heating element. Have no idea as to why they affected my A/C clutch.

Sounds like a defective ground, maybe in the wiring harness, or defective wiring in the harness. You need to get the wiring layouts ( regular and physical routes ) for the AC clutch power and O2 heater power and see how that is set up and related.

There is another live thread here where they are discussing NTK having the wrong O2 sensors in the Renix part number box.

My bet is the O2 heater wire got overheated and melted insulation in the harness and is causing a random, motion sensitive, partial short, parasitic draw.
 
Sure sounds like you still have the wrong O2 sensor, and maybe a Bad ECU now (but they can handle a lot of abuse, so lets look at the O2 sensor first)???

The Renix O2 sensor does not put out a voltage, it is a variable resistor, and the heater element is also a resistor. The ECU supplies 5.0 volts to the sensor, and the return signal wire returns the reduced voltage coming out the other side of the O2 sensor resistor to the ECU. At idle it should swing from about 1-4 volts!!!! And at 2500 rpm tighten up to 2-3 volts or tighter. The large orange wire sends battery voltage to second resistor, the heater wire-resistor). It should be about an 8 ohm resistor IIRC.

The 91-01 sensor generates its own voltage, 0-1 volts.

Put away the MT-2500 (for now) and take a volt/ohm test meter, and disconnect the O2 sensor and test the O2 sensor HARNESS ground wires, and the 12-14 volt orange wire and the 5 volt power from the ECU wire and confirm if the ECU and harness and relay, etc , going to the O2 sensor are good or not!!!

Upon trying the part store sensors (NTK and Bosch), I connected my MT2500 and they both showed a constant 4.98v output. The current sensor I have now, which is an Autolit sensor, the voltage bounces from 0.14v - 0.16v

The Autolite sensor that I have now, because the part stores sensors drained my battery, I bought on ebay because it looked like my original sensor. (ceramic with black boot on end and holes in the end that went into the exhaust). That sensor is new, it was just an older part from either a parts store or a repair shop that went out of business. And looks like it is in perfect condition.

The ebay listing showed it to be Autolite 02024 Oxygen O2 Sensor For 1987-1990 Jeep Cherokee, wrangler, Comanche. The only difference was that the connector on the autolite was a (male), connector. Wires were Grey, black and yellow. Where as my original sensor had female connector with grey, black red wires.

Looking at the 87-90 cherokee FSM, it showed that the Autolite ebay sensor was for the 2.5 liter with the yellow wire going to ignition and the grey wire going to ECU and black to ground.

Where as the FSM showed my original 4.0 sensor as having the grey to ECU, red to relay and black to ground.

Because the ebay autolite had a male plug, I replaced the it with the female plug from my original sensor. Grey to grey, black to black and red to yellow. ( I soldered the connections).

Is it possible that the o2 sensor for the 2.5 liter behaves differently than the 4.0 liter sensor?
 
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