O2 Sensor broken...

[Anonymous]

Hi Folks,

I had to take my car in to see Mr T yesterday as the engine warning light had come on  s:cry: :cry: s:cry:  

Having plugged it in to there diagnostic computer (and charging me £84.60 to do so   s:evil: :evil: s:evil:  ) they told me that the fault was with an oxygen sensor heater circuit (code P0141); specifically bank one, sensor 2.

The technician told me that this was the sensor between the main Cat and back box; is this correct?

They also wanted £170 to replace it!

Nuts to that - I'm going to have a go myself and I have found a place that will sell me a suitable one (which I think has been mentioned on here before);

http://www.gendan.co.uk/category_113.html

I know it's a 4 wire sensor, however they list two types; "normal" and "planer" so which one do I need?

I think it's the normal one, but can anyone confirm this?

Many thanks in advance...  s8) s8)

[philster_d]

You can fix this with a resistor, the heater circuit only works for a few seconds from cold.

Do a search and you wil find it.

I got about 4 from RS and a gas soldering iron I needed came to about 20 quid.

Philster.

[spit]

Ah the infamous knackered heater circuit  s:lol: :lol: s:lol:  

I think its the normal 4-wire you need. Haven't encountered the low power Planar one before.

Quicker fix as Phil says is to fool the ECU with a 15 ohm resistor across the black wires, but ideally you need something rated at least 10Watts cos they get v hot.

(That said, i used a tiny Maplin resistor for a few months on a terminal block. The resistor held up fine but the block melted  s:wink: :wink: s:wink:  )

[nafe]

Had the same problem with mine a few months back and Spit kindly fixed the problem for me ! It's still working great and the light hasn't come back on at all !    s:D s:D  

The resistor I used was from  w www.rswww.com w  and type "620-736" into the search field (without the speech marks..).

[nafe]

Oops !!! Got the code wrong.   s:oops: :oops: s:oops:  

You need to type in "160-736" (without the speech marks).

[Anonymous]

Cheers Lads...

I think I might go for the "expensive" option and just replace the sensor, after all (even if you haven't had any ill effects) it must need to work for a reason..

So is the Toyota mechanic right; is the afore-mentioned broken sensor the one between the main cat and back box?

  s8) s8)

[spit]

Aye - sensor 2 is the one after the main Cat. I've never understood why it gets the Bank 1 label though. Aaron explained it but he's on a different Mensa level to me   s:oops: :oops: s:oops:   s:wink: :wink: s:wink:

If you want to replace the whole sensor then fair-dos. the heater circuit is purely there to bring the sensor up to operating temperature so that its firing sensible voltages to the ECU. Of course, once the engine is warmed up the sensor is hot enough anyway! In addition, with this being the post-cat sensor, you won't get ANY ill effects if you go cut and shunt with a resistor. But its your call and we won't hold it against you  s:wink: :wink: s:wink:

[Anonymous]

Hmmm...

I'm starting to become convinced...

So where do I insert it?

Is it literally just between the two black wires (out of the 4) coming out of the sensor?

Would doing this not adversely affect the fueling when the car's cold?

[philster_d]

I dont think you searched ? did you

 m http://www.mr2roc.org/phpBB2/viewtopic. ... tor+heater m

[philster_d]

Just cut the 2 black wires and fix the resitor between the 2 ends where the sensor would have been.

I'm a little shocked that no-one has diagnosed this one properly yet, its got to be one of the most common Engine managment faults on this car...

Basically, Dont panic... This really isnt a problem...

The P0141 code is an advisory code, it has no effect on the actual running of the engine. Here, for the beneift of anyone who may happen to find the search button in the future, is why...

The code refers to what we call the 3rd O2 sensor, but is more accuratley called bank 1, sensor 2. There are 2 other O2 sensors on the engien, known as Bank 1, Sensor 1, & Bank2, Sensor 1. These 2 are responsible for measuring the fuel air mix that has just been burnt and exhausted by the engine. There are 2 of them because Toyota's ECU actually runs this engine as 2 seperate entities, i.e. it treats it as 2 two cylinder engines. Wierd, but effective.

The 3rd O2 sensor is fitted downstream of all the cats, wheras the 2 metering O2 sensors are fitted upstream so that they can measure the raw, un-catalysed gas coming out of the engine. Its only job in life is to measure the O2 content of the exhaust gas after the cats. The ECU then compares this reading to the one it took from the Bank 1 sensor in the manifold.  The logic it then applies to the 2 readings is astoinishingly simple:

If the 2 readings are different, and more importantly the reading from the  3rd O2 sensor is more stable than that on the manifold O2 sensor, then all is well with the world. It means that the ECU knows your cats are working as they hasve changed the make up of the gas.

If the 2 readings are the same, then the ECU knows that the cats are doing nothing to the gas at all, and lights the CEL, which prompts you do go and have your wallet lightened by your local dealer...

Becasue theres no effect on the closed loop control of the Fuelling, the engine managment makes no changes tht would effect power, or economy.

You dont actually have a failed O2 sensor though, I'd bet good money that if I hooked up my OBDII reader to your car, I'd see sensible readings coming from the 3rd O2. what you actually have, is a failed heater element.

Each O2 sensor has a built in heater inside it. The heaters are used to get the Zirconia mesuring sensors inside them up to operating temperature quickly so that they can get on with the job of measuring oxygen. This gains vital seconds in the process of gaining efficient emissions control on a cold start of the engine. Once the engine is hot, clearly anything in the exhaust flow is'nt going to be in need of heaters! The ECU monitors these heaters by measuring the current going to them, to much or too little flags up the fault code you have at the moment. The sensor itself is still working, it just takes a while to warm up... Again, having a duff heater in an ptherwise functional 3rd O2 sensor wont cause any problems with engine managment.

So, what to do to fix it? Well, you can replace the unit, or you can ignore it... Either way your car will go just as fast as its always done, using exactly the same amount of fuel. The problem with just leaving it, is that with the engine light already lit, you wont see any new problems should they occur. Fixing the thing is expensive, especially considering all you are going to gain is clear dashboard.

I appplied a bit of electrical tom-foolery to mine when it went, I simply connected a high power resistor to the heater circuit on the sensor, so that it drew the "correct" amount of current from the ECU, That way ,as  far as the ECU was concerned, the heater was working, and after 2 full start -warm up - drive -stop- cool down cycles of the engine, the light goes out. Simple...

[Anonymous]

Cheers big ears!

[spit]

Is it literally just between the two black wires (out of the 4) coming out of the sensor?

Yes. On nafe's car we cut the blacks at the sensor end and pulled them out of the sleeving at the socket end. That way, with a bit of heatshrink tubing, the resistor could be strapped up somewhere well away from the Cat or vulnerable wiring.

(This also leaves lots and lots of wire to play with if you need to graft on a new O2 in the future)

Up to you where you stick it though  s:wink: :wink: s:wink:    s:lol: :lol: s:lol:

[philster_d]

same as I have done, mine is flapping around the engine bay on the end of 2 wires   s:lol: :lol: s:lol:

[damonball]

Is it OK to use this for the O2 sensor problem?:

 m http://rswww.com/cgi-bin/bv/rswww/searc ... &Nr=avl:uk m

When i receive this do i just splice the two black wires that attach to the O2 sensor and solder them at plug end?  s:? :? s:?  Sorry, im not good with electronics!, This resistor seems quite large!?? 5cm x 1.5cm   s:shock: :shock: s:shock:  Could someone please tell me if im heading in the right direction by using this resistor as ive searched and am unsure and will it get rid of my CEL light and fault reading p0141 ?

Thanks
Damon

[heathstimpson]

With mine I removed a little bit of the black core sleeving and poked a hole in the copper cores wrapping the resistor legs through and soldering. Covered in insulation tape to hide.

[damonball]

Is this definately the right resistor though? Its quite a large one! 5cm x 1.5cm encased in a box. (see the above link). Was yours a large resistor Heath or a tiny standard one?  s:shock: :shock: s:shock:   Sorry i have no clue on electronics!  s:D s:D  

Thanks again

[damonball]

Just realised the link doesnt work!!  s:D s:D  

The resistor I have just ordered is from  w www.rswww.com w  and to view it type in ''160-736'' (without quotation marks) as suggested by nafe.

Hope its the right thing  s:? :? s:?

[heathstimpson]

Don't worry Damon it is a rather large jobbie due to the high wattage to cope with the load temp  s:wink: :wink: s:wink:

[damonball]

Sorry to ask again but I'm still unsure  s:cry: :cry: s:cry:   Do I have to cut the black wires completely or do i just splice them and bridge the resistor across the two black wires so the plug and 02 sensor are still connected?. If i have to cut the black wires, does the resistor bridge the wires coming from the plug or from the O2 sensor??

Thanks again guys
No more questions after this one!!  s:D s:D

[kanujunkie]

cut the 2 black wires at the SENSOR end and splice in the resistor, the wires in the o2 sensor are nickel plated or of high nickel content and as such will be almost impossible to properly solder, so create some flyleads on the resistor and splice them in

[heathstimpson]

cut the 2 black wires at the SENSOR end and splice in the resistor, the wires in the o2 sensor are nickel plated or of high nickel content and as such will be almost impossible to properly solder, so create some flyleads on the resistor and splice them in

No wonder I struggled to solder. I found by stripping a little bit of the sleeving off and making a hole between the cable strands allowed the resistor legs to be wound within the cable and the solder held good for me. Saved me cutting the black wires  s:wink: :wink: s:wink:

[StuM]

Hi All,

Is this (rather basic) diagram representative of where the resistor needs to go:

 

I've left out all the untouched wires, showing just the two black ones.

Does the 'direction' matter?

Thanks,
Stu

[CMH]

Huge thanks to spit and all on this forum for all the help with the P0141 resistor fix.  It worked like a charm.  I liked this method -

With mine I removed a little bit of the black core sleeving and poked a hole in the copper cores wrapping the resistor legs through and soldering. Covered in insulation tape to hide.

- so much that I did the same.  Drilling 2 small holes in the alloy heatshield towards the centre of the engine bay allowed me to bolt the resistor on, then I loosely cable tied the wires up out of the way before leading them round in the groove half way up the cooland bottle.  That was just the right height to lead the wires into the plug end of the cable.  Engine management light went out when I applied an ODB2 code reader.  Result!  I'd put up some photos if only I could work out how....

[CMH]

Have now worked out how to post photos, so here they are - with the text from my last post they should be fairly clear...

[spit]

Excellent thread resurrection Mark   s:wink: :wink: s:wink:  And a tidy install too. Mounting the resistor is a great idea and puts our 'just dangle it' efforts in the shade!

For anyone stumbling across this thread, we've now drifted away from the 15 ohm fixes mentioned above. 27ohm, 50watt wirewound resistors are now the fix of choice and seem to work well. Nic - your Club Chairman - has personally funded a small stock of these. A fiver into Club funds will get you rolling.