Heated Oxygen Sensor

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.

Had the same problem on my '04 GC. Started with a P0031, replaced the O2 sensor with one of the Universal Bosch sensors where you have to wire the adapter. Didn't get rid of the P0031 and a P0135 appeared. Tried a bosch sensor with the correct adapter. Before installing the new one I checked the voltage readings on the engine sidde wiring. The Bank 1 Sensor 1 wiring read the same as the other O2 sensors. Once installed, P0135 cleared but P0031 came back the first time I started it up after clearing the codes.

I'll try an OEM sensor from the dealer. If that doesn't work probably have my mechanic look for a short. Of course this is all happening when I have to get it smogged for this year's registration. :banghead:

Thanks to all who posted possible solutions.

Followed this thread, hope some of you are still around. I havbe a 2004 JGC 4.0 liter. Failed emission test indicating O2 sensor problem. Replaced all 4 sensors but drawing codes PO31 and PO51. I used Bosch sensors which I hear Jeep has a problem with. BUT, why am I only getting codes for the two upstream sensors and not the two downstream sensors? so I noticed the #16 fuse was blown - I replaced it and started the motor. it promptly blew again. I then disconnected both upstream sensors at the connectors and started the motor. The fuse did not blow. Repeated this several times and the fuse did not blow. I then connected only the front upstream sensor and started the motor, the fuse did not blow. Then disconnected the front upstream sensor and connected the rear upstream sensor. this time the fuse blew when i started the motor. So, only the rear upstream sensor caused the fuse to blow. Really confused, does the fact that the fuse doesn't blow with both upstream sensors disconnected mean something? Why am I getting a code on the front upstream sensor if it's not blowing the fuse? I really hope someone can help - facing a deadline with emissions in 10 days.

The description for codes P0051 and P0031 are the same:

Shorted condition detected in the oxygen sensor heater element control feedback sense circuit.

So it's likely a shorted wire.
Why am I getting a code on the front upstream sensor if it's not blowing the fuse?
If you ran it with the upstream sensor disconnected it will trigger a code.
It doesn't have to blow the fuse to trigger a fault code, if the voltage is wrong it shows a code.
I would check the continuity of the wiring harness to all the O2 sensors for any shorted or open wires. It's possible a short in one sensor is causing the other to trigger a code. Once the problem is corrected with one sensor bank it may clear the error code in the second sensor bank. It takes a preset number of successful run cycles to clear, but I don't remember the how many. Some codes can be manually cleared with an OBD II tool.
If the wiring is fixed or shows ok and still triggers codes, it's possible you have a defective or non compatible O2 sensor(s).
Good luck.

Bob, thanks for the reply. I purchased new o2 sensors - NTK brand. and will replace first to see if that works. if not, i guess i have a shorted wire. hope that's not it. thanks for your reply.

You're welcome. Let us know how it goes.

Well, that didn't do it. Replaced the rear upstream sensor with a NTK brand but it's still blowing the fuse and giving me a PO 31 & 51 codes. Taking it to a mechanic to check the wiring at the connector. So we'll see.

Hi,I have also had this fault code come up today. But as luck would have it,mine is sorted,so I shall commence it what I found to be the problem. Just recently got myself a grand Cherokee 4.0l mk2 2000 model. The heat resistor was faulty resulting in no heat or fan working. I removed the resistor to find the plug slightly melted,hence bad connection. Well I like most tried the cheapest option. wiggle the wire and tie strap it where contact is made,hence heaters now work. Well so I thought. Last night I took my boy to his Xmas assembly,cold night,and heaters packed up!. Me being clever,or shall I say NOT! got out the car to the passenger side moved the cable on the resistor,heaters now working. But car running a little rough,, Yikes!.. Checked with diagnostic machine,up comes the error code,P0135.. O2 heater sensor,well my idea is O2 heater sensor,hence heater,would perhaps mean heater resistor. Well next day I decided to disconnect the earth terminal on battery for 15mins to reset the ecu,reconnect,to find heaters or fan not working,but the Jeep is running sweet again.. So think I better bite the bullet and buy a new heater resistor as the fault in the connector was causing the code,and the car to run rough,so guys as this is a common fault with heat resistors,perhaps check for short in the wiring here.. Simple fix,hope it works for some of you,I hope to hear it does,Good luck..

Well, that didn't do it. Replaced the rear upstream sensor with a NTK brand but it's still blowing the fuse and giving me a PO 31 & 51 codes. Taking it to a mechanic to check the wiring at the connector. So we'll see.
I would look at the wire feeding the two oxygen sensors. Look for where the wiring could touch the exhaust system. Follow the wires up to the fuse box. Disconnect your battery ground unbolt the relay center and look for corroded wiring underneath where the wires connect. Also check where it goes through the firewall.

The clue is the word "heated". Is your engine running at the proper temp? If not, try changing the thermostat.

Dude i think it means the electrical connection on that particular O2 sensor either has disconnected because in my jeep i was also face the same problem or may be connection is need to be clean..

Has anyone got an idea what the key on (not engine running) voltage should be from fuse #16 under hood in PDC?

I have tried everything to get rid of a P0051 but no luck. I found that when I pull the fuse and check the voltage at #16 that it only puts out about 3.5 compared to the 12 volts in all the other slots.

That is the only thing I can think is causing my P code.

Thanks in advance for any help.

Oh, by the way. 1999 Jeep Grand Cherokee Laredo, 4.0 I6 with Ca. emissions.

Without a wiring diagram I can't be sure but I think you have resistance in the circuit. I would disconnect the ground and turn the fuse holder upside down and look for corrosion. If this feeds the oxygen sensor try using an inline fuse holder and a 12 volt feed.