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Unread 06-29-2006, 05:36 PM   #1
Flyusaf2002
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Trouble Code PO138

Hi all,

The code that came up on my 99 TJ 2.5 is a PO138 - "THe input voltage from O2 Sensor number 2 in Bank 1 is too high for current operating conditions". Can anyone give me some information on this problem?

Can I still drive my jeep - it run just fine, maybe a bit rough at idle, but otherwise seems okay. If I get to this problem in a few weeks, have I waited too long/am I causing long term damage to my jeep?

I appreciate help, I'm currently going through a military school and have very limited time, so I'd love to delay launching into the project for a few weeks.

Thanks,
Andy

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Unread 06-29-2006, 05:53 PM   #2
Jetmech143
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Replace the sensor???
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Unread 06-29-2006, 06:02 PM   #3
Flyusaf2002
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I don't know understand whether or not the sensor is broken and the engine is fine, or, the sensor is accurate and somthing is seriously wrong with the engine? Does anyone have any better detail than the simple diagnosis from the code reader?

Thanks,
Andy
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Unread 06-29-2006, 06:43 PM   #4
Slithering_Joe
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Not sure if this helps but mine once in a while will store this code as a pending code which will not illuminate the Check Engine Lamp (CEL). All readiness monitors check out OK though. By the next day the pending code is gone. And yes, the CEL does work. This code should not casue a driveability problem such as a rough idle. That sensor in question monitors the catalytic convertor.
Did your CEL illuminate?

Edit: The description I have is "...O2 sensor shorted HI." In the scope of things, I'm not sure what that really means. A short brings the voltage low.
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Unread 06-29-2006, 06:46 PM   #5
Flyusaf2002
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Yes, my Check Engine Light is on steady. Also, the Catalytic Converter is relativly new - dealer installed (warranty) approximatly a year ago.

Andy
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Unread 06-29-2006, 06:55 PM   #6
Slithering_Joe
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If you have mileage above 60,000 miles it could be a bad O2 sensor. You may want to check the resistance in the wiring from the PCM down to the O2 sensor. A high resistance will show a break/open circuit or a corroded wire in the harness. I'm mentioning this as a possible test to avoid throwing parts at the problem.

According to a Chrysler '98 Service manual:
PCM, BLK Connector
PIN WIRE DESCRIPTION
---------------------------
A25 TAN/WHT O2 Sensor SIGNAL (*)
A4 BRN/YEL SENSOR GROUND/RETURN (*)

DOWNSTREAM O2 sensor connector
TAN/WHT O2 Sensor SIGNAL (see * above)
BRN/YEL SENSOR GROUND/RETURN (see ** above)
FUSE 21 (20A) feeds ORG/DK GRN wire to the 12V+ heater circuit on O2 Sensor
BLK wire GROUNDS O2 Sensor Heater Circuit
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Unread 06-29-2006, 06:58 PM   #7
Flyusaf2002
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Thanks joe - I've got 56000 miles, so i'm right up close to that border. Does Anybody have an idea what the cost of a new 02 sensor is?

Andy
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Unread 06-29-2006, 07:05 PM   #8
Slithering_Joe
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Quote:
Originally Posted by Flyusaf2002
Thanks joe - I've got 56000 miles, so i'm right up close to that border. Does Anybody have an idea what the cost of a new 02 sensor is?

Andy
They range about $60 to $100. Don't buy Bosch! Get Mopar (OE) or Denso.

maybe check www.oxygensensors.com I have no experience with them. just popped into my head.

For the downstream O2, I got 95,000 on my TJ and 107,000 miles on my Mustang. Since my Mustang has homemade MIL Eliminators I guess that doesn't count.

PS: Don't buy Bosch brand.
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Unread 06-29-2006, 07:15 PM   #9
Flyusaf2002
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Verdict?

So, what's the verdict, can this problem wait a few days (and about 150 miles) or must it be done tomorrow? Again, the idle shows only the smallest rough spots, and the jeep drives just fine, however, the CEL light is remaining on constantly.

Thanks for all the help,
Andy
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Unread 06-29-2006, 07:23 PM   #10
Slithering_Joe
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Quote:
Originally Posted by Flyusaf2002
So, what's the verdict, can this problem wait a few days (and about 150 miles) or must it be done tomorrow? Again, the idle shows only the smallest rough spots, and the jeep drives just fine, however, the CEL light is remaining on constantly.

Thanks for all the help,
Andy
I think you are fine. If you have a short than I would get it fixed as soon as possible. Don't be alarmed. The PCM has a lot of protection built into it. Your idle has nothing to do with the problem you are having on the downstream O2 sensor (aka O2 Sensor 2). It just monitors the catalytic convertor.

One thing though, if the Cat was replaced under factory warranty, the O2 sensor and all the way up to the PCM should also be covered!
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Unread 06-30-2006, 07:34 AM   #11
Flyusaf2002
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My jeep is a 99, I believe that thewarranty that would cover such a fix only lasted for 6 years/60,000 miles. While i'm within the miles, I'm over on years. Did my warranty get extended when they installed a new Cat?

Lastly - is this a problem that I should let a dealer look at, or can any midas,monroe,mastercare give me a hand on it? Thanks for the help,

Andy
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Unread 06-30-2006, 09:31 AM   #12
scottheath5499
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You can forget the warranty. Also, you can drive the Jeep. The downstream O2 sensor monitors your emissions. You most likely have a bad O2 sensor. They simply screw into your exhaust pipe just after your CAT. 7/8" wrench. Buy one from the dealer at about $100 and replace it yourself. Disconnect the negative lead on your battery for about 10 minutes to clear the CEL. Good to go!
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Unread 06-30-2006, 10:09 AM   #13
Slithering_Joe
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Let us know what you did to fix the problem.
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