Last week the exhaust and cat were replaced on my late 97 Cherokee 2.5 petrol. The threads on the O2 sensor were stripped so I fitted a brand new one.
Today I plugged in my diagnostic sensor and got a - 02 sensor no 2 High voltage message !.

The Jeep runs OK but the cat and exhaust are blue - as if I have been driving hard, which I haven't.

Is this common ?.

 

Owl,

I am a product specialist with Walker Products, a manufacturer and world wide distributor of oxygen sensors. What you are describing is not normal and possibly indicates that the exhaust gas is somehow being trapped in the system. Having your new cat and ignition timing checked out would be the next steps in my opinion.

 

Hello, I think the cause of the problem is that the Cat and exhaust were cheap after market products - costing about a third of Jeep parts !.

The Jeep is running okay my friend owns a garage so I will ask him to check it out.

 

A few people have reported this code and some similar behaviours coming up due to poor wiring. Namely the wires feeding the O2 sensors can rub against the drive shafts and short out. I'd recommend climbing under there and giving it a look

 

X2^ Check the wires. Also the 02 heater is on a relay, and maybe it's own fuse. (the wire shorting might blow the fuse). Timing is controlled by the PCM and is not adjustable.

 

O2 high is indicating a rich condition. Of course you DID clear the long term memory by disconnecting the battery AT LEAST 8 HOURS.
The new exhaust is acting differently than the old one - but the computer doesn't know it's been changed.

There are lots of ways people CLAIM clears the memory, flashing lights, cycling the key etc. All they do is clear the codes, not the long term memory.

 

What code was it? P0XXX?

 

The code is P0138

 

The code is P0138

I don't know if I should clear it and see if it pops up later ?.

 

it will continue to run rich for quite a while - code or no code - until the deep memory finally resets itself. That takes many drive cycles. By then you may have killed the cat from overheating.

Or you can clear the deep memory yourself by the 8 hour disconnect.
Just clearing the codes won't change things, the code will come back. YOU HAVE TO DEEP CLEAN IT! -- or live with it.

same like reading a news report you don't like - you can tear up the newspaper, but it does not change the event.

 

I had a couple codes going: P0138 and one for the cat not working. Apparently my '96 Cherokee never had the Cat/ECM recall and the cat was really, really bad. I bought a couple Oxygen sensors and made an appointment at my local Jeep dealership to have the recall performed. They ordered a new cat, installed it, updated the ECM, installed the new Oxygen sensors I provided and I was off.

P0138 did not appear immediately but it did after 10 miles of driving. I went back to the dealership and since it wasn't directly related to the cat, I wasn't going to push for them to figure it out on their dime.

I did a lot of research: I checked the fuse (it was good), checked the ground (it was good), I even cleaned up all the battery terminals and all seemed well. I checked both the oxygen sensors and they were connected and in tight with no leaks. I really had no freaking idea. At least until I checked beyond the oxygen sensor connections. It appeared that just beyond the rear (downstream, just after the cat, before the muffler) oxygen sensor male connector (that comes from the vehicle), one of the wires was completely frayed from the connector - thus unable to send information to the ECM. I cut the connector off the oxygen sensor and the connector from the vehicle and spliced the wires together - taking time to make sure the wires matched up as the connector would have it - just take the time and write everything down.

VOILA! BINGO! THAT'S THE WHOLE ENCHILADA! That was my problem - a stupid frayed going into the male connector on the downstream oxygen sensor. I started the Cherokee up, cleared the code, and drove 40 miles for about an hour and a half. No code! I think I got it, Johnny!

 

The p0138 really means its not reading the correct amount of voltage from the heater circuit on the 02 sensor thus triggering a CEL i just fixed that code on my truck i bought a new sensor