P0138 on 2000 Jeep TJ

I recently had the codes checked and found P0138, I cleared it, but in short drive later it was back, the vehicle runs fine, but I do notice it is running rich when backing into the garage, any ideas what would be causing this?

Rob

the 02 sensor or the wiring/ circuit to it!

any idea how to tell which 02 sensor it would be? or how do I determine which one?

P0138 - O2 Circuit High Voltage (Bank 1, Sensor 2)

So its the one after the CAT on bank 1. I don't know that it would cause the truck to run rich.

yeah I'd be suspicious of that as well! Is it misfiring at all? what size engine?

it's the inline 6cyl 4.0L, no misfire at all, it runs great.

well try the sensor then but check the wiring and any fuses as well that may say 02 sensor! otherwise the new sensors heter circuit won't work if the fuse for it's power is blown!

I have the same problem,the 02 sensor behind the cat was replaced,the car runs in nutral the whole day as I take for a ride after about 3 miles it cuts of, after 3 to5 sec I start it again runs back for 2 miles and cuts off again and this repeat for about 2-3 time after that stop compleetly and then have to waith for couple of hours and then it start again and start doing the same alover again .can ome one help me frustradetd
Rob

Check fuel pressure.

When was the last time the fuel filter was replaced?

Also, check exhaust back pressure.

Goodluck and keep us posted.

Check exhuast back pressure and recheck your 02 and it's circuit! My own opinion is that alot of aftermarket brands of 02 sensors don't heat up enough to keep the code parameters happy

I have a 2001 Jeep Wrangler TJ with 136K miles.

I replaced the back O2 sensor for the first time a couple hundred miles back. (I had replaced the front O2 sensor at around 100K miles but didn't know there was a back sensor until recently.) The vehicle runs much better, more pep, can't tell if there is any gas mileage improvement. The check engine light is on and I get a P0138 and a P0138 Pending code which clear but then come back on.

I've been told the the fuel filter is in the fuel pump inside the fule tank instead of inline and that you shouldn't touch it unless there has been fuel contamination. I feel that after 136K miles I should change the fuel filter based on some of the replies to this code and the fact that the O2 sensor is new.

Any suggestions?

Thanks.

Bill

A fuel filter will not repair that dtc and if it's the sock on the end of the fuel pump then it'd be a waste of time to change it unless you're doing it for practice and wish to replace the entire pump assembly while you're in there. What brand of 02 sensor did you use? How many are on your Jeep? 2?, 3? 4?. How competent are you with a dvom and a wiring diagram to check the 02 circuits? Any blown fuse that says 02?

Answers to your questions:

• Bosch 02 sensors. Upstream and downstream. Different p/n per fitment catalog.
• Total 2 sensors - (1 in downpipe after exhaust manifold & 1 after cat, before muffler)
• There is 1 fuse for both 02 sensors and it ohms out as a short.
• There is a relay marked 02 sensor in the power distribution center. It has the same p/n as the horn relay. I swapped them and the horn still worked and I still got a check engine light.
• I can use a dvom. I have attached the only schematic that I have. I don't know what the "good" voltage should be at pin 4 on the downstream sensor. Since the upstream and downstream O2 sensors have different part numbers, I don't know if they should read the same or not.

BTW - Earlier today, before doing any of the reseating of fuses and relays, the check engine light was on. There was no code. I reset the light and after the engine ran for a couple of minutes the check engine light came back on. I checked this 4 times throughout the day with the same results (No code, light on.)

So they're bosch? I'd probably return it and get one from the dealer!

No that's not what i was referring to it's a dead post why pull it up? To sell parts?