O2 Sensor Problem... - JeepForum.com
 
LinkBack Thread Tools
post #1 of 3 Old 10-16-2013, 10:25 PM Thread Starter
mlautner03
Registered User
2005 TJ Wrangler 
 
Join Date: Oct 2013
Location: Buffalo
Posts: 97
O2 Sensor Problem...

Hi i'm new here, but i'm curious if anyone can relate to the problem i'm having. I have a '99 Cherokee Limited with a straight 6. My check engine light has been on for code P0138 and i'm having a hard time narrowing down the exact issue. What it does is sometimes (probably half the time) when I start driving it will nose over and run real choppy. It does it mostly when the engine is still cold. Occasionally at idle (like at a stop light) the RPMs will drop and it will almost stall. And there has been a couple times while standing outside it (while it's running) you can smell it's running very rich and it will actually stall.

I've changed the plugs/wires and cap/rotor. And i've changed both O2 sensors. I did replace the downstream twice thinking one was defective but still didn't solve the problem. I was told by a knowledgeable source that the O2 sensors actually aren't working.... for whatever reason. I did have a problem awhile back where the wires were pulled directly out of the downstream O2, but the plug wasn't damaged. So I just replaced it (the O2 Sensor). Is there a chance when the wires were pulled out it shorted something?

I'm very much a novice and not mechanically inclined but starting to get frustrated... just hoping someone can narrow down the problem a bit for me. Or at least point me in the right direction. Thanks

Mike

mlautner03 is offline  
Sponsored Links
Advertisement
 
post #2 of 3 Old 10-17-2013, 12:16 AM
jnicewan
Registered User
1995 ZJ 
 
Join Date: Dec 2010
Location: Norman
Posts: 2,340
How many oxygen sensors do you have? I thought the 99+ 4.0's had 4. Are you sure you replaced the correct 02 sensor? P0138 is the bank 1 downstream voltage too high (H02S-12). If you have the 4 sensor system just make sure you are looking at the right one. If you had a scanner that could monitor live data you should be able to see what the sensor is reading when the failure is present. Oxygen sensors normally produce a voltage around 0.2-0.8 volts, the downstream sensors should produce a more steady reading usually around 0.4-0.6v while the upstreams should be constantly switching between 0.2-0.8v when running. I think that code gets triggered when the voltage exceeds approx 1.2v maybe a little less. If you see a voltage higher than 1-1.2 volts then unplug the sensor and see if the voltage goes away, if not then the wiring is shorted to power somewhere, if the excessive voltage goes away after unplugging the sensor then the sensor is faulty.

Does this pic of the exhaust/sensors match what you have? If so the sensor you would be looking for is the #4-1/2 in the diagram.
jnicewan is offline  
post #3 of 3 Old 10-18-2013, 04:48 PM
uberxj92
Registered User
1992 XJ Cherokee 
 
Join Date: Oct 2012
Location: umatilla
Posts: 1,961
99 xj has 2 o2's

http://www.jeepforum.com/forum/f177/92-xj-sadness-2075657/index2.html
uberxj92 is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.



Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may 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 On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome