Ok, my 2003 Jeep GC Limitied 4.0 engine light came on again and this time the code is P 0031, which is 02 Sensor Heater Control Circuit Low (Bank 1 Sensor 1).

Where is Bank 1 Sensor 1?? So I can replace it myself. Should I replace the oxygen sensor in other bank? Thanks in advance.

I hope to find this out too. What I can tell you is that on FLM's that have eight cylinders Bank 1 is on the side with the number 1 plug. Sensor 1 is upstream or before the cat convertor. Bank 2 is on the side with the number two plug and sensor 2 is downstream or after the cat convertor. I haven't been under my 98 4.0 JGC but will when the weather warms up.

Forgot to add ( the other sensor) If it ain't broke don't fix it.

now what??? After replacing the oxygen sensor with a Bosch brand.....now i am getting a new error code....P 0135.....Heated Oxygen Sensor Bank 1 Sensor 1 malfunction. What's the deal?

Have you erased the previous code before replacing the sensor? Erase the 0135 and see if it reappears.

yup. code P0135 wasn't there before i changed the sensor. It was just P0031 and then changed the sensor. Unhooked the battery to clear the code. Now its saying P0031 and p0135

yup. code P0135 wasn't there before i changed the sensor. It was just P0031 and then changed the sensor. Unhooked the battery to clear the code. Now its saying P0031 and p0135
There have been a lot of complaints about after market 02 sensors, especially Bosch, when used on newer Jeeps.

The P0135 Oxygen sensor heater element fault code could also be due to a short, open or high resistance in the wiring harness or harness connectors. Also check fuse # 16 in the under hood Power Distribution Center. (Although unlikely since one fuse is used by all 02 sensors I think and the code is only for one)

Here is a more detailed description about code P0135/Heated Oxygen Sensor:

The heated circuit in the oxygen sensor decreases time needed to enter closed loop. As the O2 heater reaches operating temperature, the oxygen sensor responds by switching according to oxygen content of the exhaust surrounding it. The PCM tracks how long it takes for the oxygen sensor to begin switching. If the PCM determines (based on coolant temp) that too much time elapsed before the oxygen sensor began operating properly, it will set P0135.

In simpler terms, the 02 heated circuit heats up the 02 sensor electrically rather than waiting for exhaust gasses to warm it up and allows the engine to transition from open loop (fixed, pre-programmed fuel mixture and other engine settings) and reach closed loop (variable engine settings) operation sooner. The after market sensors sometimes have a problem pre-heating the element properly. I'm willing to bet your Jeep runs fine after it reaches operating temperature, (but with possible reduced mpg if it's staying in the richer mixture, open loop mode) it's the open loop/closed loop transition where the PCM induces a fault code due to lack of or incorrect pre-heating.

I would first check all the wiring and fuses associated with the 02 sensor for continuity, if you still get the code return the Bosch sensor and replace it with an OEM sensor.

yup. code P0135 wasn't there before i changed the sensor. It was just P0031 and then changed the sensor. Unhooked the battery to clear the code. Now its saying P0031 and p0135

How much time must elapse with the battery disconnected before the codes are erased? This doesn't always work on Ford/Lincoln/Mercurys.

How much time must elapse with the battery disconnected before the codes are erased? This doesn't always work on Ford/Lincoln/Mercurys.

I waited like 5 minutes....

There have been a lot of complaints about after market 02 sensors, especially Bosch, when used on newer Jeeps.

The P0135 Oxygen sensor heater element fault code could also be due to a short, open or high resistance in the wiring harness or harness connectors. Also check fuse # 16 in the under hood Power Distribution Center. (Although unlikely since one fuse is used by all 02 sensors I think and the code is only for one)

Here is a more detailed description about code P0135/Heated Oxygen Sensor:

The heated circuit in the oxygen sensor decreases time needed to enter closed loop. As the O2 heater reaches operating temperature, the oxygen sensor responds by switching according to oxygen content of the exhaust surrounding it. The PCM tracks how long it takes for the oxygen sensor to begin switching. If the PCM determines (based on coolant temp) that too much time elapsed before the oxygen sensor began operating properly, it will set P0135.

In simpler terms, the 02 heated circuit heats up the 02 sensor electrically rather than waiting for exhaust gasses to warm it up and allows the engine to transition from open loop (fixed, pre-programmed fuel mixture and other engine settings) and reach closed loop (variable engine settings) operation sooner. The after market sensors sometimes have a problem pre-heating the element properly. I'm willing to bet your Jeep runs fine after it reaches operating temperature, (but with possible reduced mpg if it's staying in the richer mixture, open loop mode) it's the open loop/closed loop transition where the PCM induces a fault code due to lack of or incorrect pre-heating.

I would first check all the wiring and fuses associated with the 02 sensor for continuity, if you still get the code return the Bosch sensor and replace it with an OEM sensor.

That is what I am afriad of.....I've read several topics about Jeep disliking Bosch brand oxygen sensors. I guess I will have to take it back to Advance Auto. But, where can I find an OEM parts for the Jeep? How about Denso? I will not go to Jeeps dealership for Mopar parts since they are usually way overpriced. Ebay would be my best choice, right?

Also, i will check the wiring and fuse.

That is what I am afriad of.....I've read several topics about Jeep disliking Bosch brand oxygen sensors. I guess I will have to take it back to Advance Auto. But, where can I find an OEM parts for the Jeep? How about Denso? I will not go to Jeeps dealership for Mopar parts since they are usually way overpriced. Ebay would be my best choice, right?

Also, i will check the wiring and fuse.
I wouldn't buy one from Ebay, why risk more headaches?
If the electrical circuit checks out I suggest just buying one from the dealership, they're only a few bucks more and discounted if you buy online.

they don't make the same oxygen sensor anymore so I ordered a Denso brand.

Got my new Denso heated oxygen sensor from rockauto.com to replace the Bosch brand.....but dang connector didn't fit and the wires are too short. How can they send me a part which they say will fit my Jeep? I put the old heated sensor back in and erased the codes. Now only one code comes up....P 0031. Back to square one.

Do not get Bosch for the Jeep! Jeep hates Bosch!

Now I need to find the right Denso part or maybe an AC Delco heated sensor?

Denso or NGK will work. Bosch is a no no in Chryslers. So why not extend the wires and use the connector from the old one?????

Doesn't cutting the wires and using the connectors affect the PCM?

No.

Doesn't cutting the wires and using the connectors affect the PCM?

I just put in a new Denso oxygen sensor and disconnected the battery...P0031 came back again. What else can be wrong with it? I had already replaced the Idle Air Control and Throttle Position Sensor....

what about oxygen senor relay?

This has got to be kidding me! A new error code. P0505. IAC. I just replaced it last month because of the same code(P0505). I am guessing there is a short in the wires somewhere.

Both of your codes point to a short in the wires somewhere........

This has got to be kidding me! A new error code. P0505. IAC. I just replaced it last month because of the same code(P0505). I am guessing there is a short in the wires somewhere.

There is defintely a short.....I was walking to the Jeep after grocery shopping and I saw that the brake lights were still on.

I don't even know where to start looking for a short.

I feel you pain on this one. I am going through the same thing with my wifes GC. To start, I had P031, P051, and P0136. Ours is a Cali Spec so it has 4 sensors. I replaced all 4 with Bosch. Still had the same codes. Ran out of time to diagnose so brought it to a trusted mechanic. He found out that there was a short. If you follow the fuel rail thats to the right of the valve cover all the way towards the back near the firewall, there is a stud that sticks up out of the motor. The wiring harness runs right along that, and our wiring harness had been rubbing for years on that bolt until finally there were 3 wires that chaffed through and were shorting out. So he fixed them, and good to go......................................

until the day after. The light came on again. P0135. So I replaced the upstream sensor with Bosch again. Problem went away for a day and a half. Cut to this past Monday, and the light came on with this code again. I had the light reset and it came back. And the other day my wife said the guages were acting all weird and the car acted funny. It only did this once.

Basically right now, the light and code P0135 is still there. At this point I don't know. I am thining now about replacing the sensor with OEM. However, the guage thing makes me wonder if the PCM is messed up. My mechanic said that when the wired shorted it could have messed up the PCM. I will have to take it back to have him check that. So far, all the other Bosch sensors have been fine.

Anyway, check your wiring harness towards the back of the motor at the firewall and you may find your shorted wires.

Chryslers dont like Bosch plugs and O2 sensors. Replace the Bosch sensors with Denso or NTK/NGK. Your other problem might be a bad crankshaft position sensor making the guages do weird things.

I feel you pain on this one. I am going through the same thing with my wifes GC. To start, I had P031, P051, and P0136. Ours is a Cali Spec so it has 4 sensors. I replaced all 4 with Bosch. Still had the same codes. Ran out of time to diagnose so brought it to a trusted mechanic. He found out that there was a short. If you follow the fuel rail thats to the right of the valve cover all the way towards the back near the firewall, there is a stud that sticks up out of the motor. The wiring harness runs right along that, and our wiring harness had been rubbing for years on that bolt until finally there were 3 wires that chaffed through and were shorting out. So he fixed them, and good to go......................................

until the day after. The light came on again. P0135. So I replaced the upstream sensor with Bosch again. Problem went away for a day and a half. Cut to this past Monday, and the light came on with this code again. I had the light reset and it came back. And the other day my wife said the guages were acting all weird and the car acted funny. It only did this once.

Basically right now, the light and code P0135 is still there. At this point I don't know. I am thining now about replacing the sensor with OEM. However, the guage thing makes me wonder if the PCM is messed up. My mechanic said that when the wired shorted it could have messed up the PCM. I will have to take it back to have him check that. So far, all the other Bosch sensors have been fine.

Anyway, check your wiring harness towards the back of the motor at the firewall and you may find your shorted wires.

thanks for the info about the shorting. i will look into it this weekend.

bosch is crap i'd stick with oe or use the ngk branded ntk o2's you can get them at www.ngk.com as well as ngk plugs which are about the best copper plugs you can get your hands on. Also i don't know about the post any of the newer models with the 2 upstream sensors like my 04 but i had ntk sensors on my 99 and they worked great. it ran smoother and never had a problem with it until someone wrecked me. hope this helps for further issues.