P0135 & P0141 Fault Codes (o2 Sensor Heater Circuit Bank 1 Sensor

MUDGUTS · July 23, 2015

Hi,

I've recently bought a 2004 GS 300. Before that I had an LS 400.

I'm impressed and it's running well apart from the Check Engine light. I used a code scanner to find the codes:

P0135 & P0141 fault codes (O2 Sensor Heater Circuit Bank 1 Sensor 1 / 2)

I've cleared these but the light has come back on as I expected.

My question is about a fuse for these sensor heaters? I've done a bit of research on the web and suspect it's something common like a fuse but I can't find any reference to where this could be.

If I can rule this out them I'm left with a wiring problem.

Thanks in advance for any suggestions.

ColinBarber · July 23, 2015

There are no fuses. The heater circuit is powered directly from outputs on the engine ECU.

Heater coils are common failures for O2 sensors, especially at an age of around 7 or 8 years onwards. The issue you have is that you don't know if these two faults happened at exactly the same time or at different times. It is very possible that the two O2 sensor went bad within a short space of time however if the faults occurred together then there is more likely to be a common fault such as a bad Battery earth, or bad earthing to the engine - if this was the case and the fact that the errors come back after being cleared would mean there is still a common electrical issues.

I would imagine the more likely scenario is that the previous owner ignored the CEL after one O2 sensor failed and then the other one failed, which means you need to replace them both. You should measure the resistance of the heater circuit directly on the sensor connector as a test, they are probably open circuit.

MUDGUTS · July 24, 2015

Thanks very much for the info Colin.

Incidentally I needed to have the Battery replaced this morning as the old one was flat again (RAC checked it and discovered one cell was not working and it was not taking a charge) anyway...

I've no idea why but the Check Engine Light has now gone out. I don't know if this could be related to the Battery change, in any case I checked again for fault codes and discovered none. The VSC light and another were triggered by this but I managed to clear them by bridging the two pins as in the guide by TigerFish.

I'll keep an eye on this and report back. I'll probable end up getting it looked at.

ColinBarber · July 24, 2015

A weak Battery can cause random errors to appear. If the heaters are faulty the error should come back very quickly. Let's hope it was just the Battery.

MUDGUTS · July 26, 2015

Sadly the light is back on. I'm going to live with this for a while and monitor fuel consumption, which seems OK at the moment. I'll keep you all informed.

MUDGUTS · July 28, 2015

You should measure the resistance of the heater circuit directly on the sensor connector as a test, they are probably open circuit.

Excellent advice Colin, I tested the resistance at the plug. I used the two black wires. Both o2 sensors indicated open circuit.

Given that the sensors are quite easy to access, I'm going to replace them myself.

What I'm looking for now is a reccomendation as to where to source. Obviously Lexus will be quite expensive.

dave1 · July 29, 2015

You should measure the resistance of the heater circuit directly on the sensor connector as a test, they are probably open circuit.
Excellent advice Colin, I tested the resistance at the plug. I used the two black wires. Both o2 sensors indicated open circuit.
Given that the sensors are quite easy to access, I'm going to replace them myself.

What I'm looking for now is a reccomendation as to where to source. Obviously Lexus will be quite expensive.

My local garage sourced an o2 sensor for my GS430, Denso, not expensive. He had no problem at all, just looked in his system online and got it. Can't remember exact cost but I think it was around £50. I can check if it would help.

MUDGUTS · July 29, 2015

Thanks for this info Dave, I'll have a word with a local parts supplier, Denso seems to come up in search results quite often, so I think these could be a reasonably priced alternative to the Lexus originals.

ColinBarber · July 30, 2015

The Lexus originals are Denso - Toyota own a large part of Denso (around 25%).

MUDGUTS · August 11, 2015

I was thinking, before I go ahead and replace these, as it's only the heater circuit in each sensor that has failed (verified by fault codes and checked with a multimeter as open circuit), could I just join the heater circuit wires up to fool the ECU and clear the fault code?

I've heard about O2 Sensor resistance values of 12 Ohm, is this for the actual sensor or the heater? Even if that were the case, could I buy a 12 Ohm resistor from Maplin and put that in?

ColinBarber · August 16, 2015

The resistance spec is between 11 and 16 ohms - this is for the heater circuit. You don't measure resistance of the actual O2 sensor as a way to determine if it is faulty or not.

You could use a resistor if all you want to do is clear the code, doesn't help with getting the sensors up to working temperature though.

If you assume the voltage going to the sensor is around 14v once the engine is running then if you used a 14 ohm resistor the current would be 1 amp. The wattage of the resistor needed would need to be at least 14 watts (14 volts x 1 amp). It would get very hot so you need to make sure it doesn't burn anything nearby.

MUDGUTS · August 16, 2015

Thanks for the input Colin,

I've ordered a Bank 1 Sensor 1 sensor from Eco Lambda:

http://www.ecolambda.co.uk/main/ecosale/price.pl?item=250-24137

This is the easiest of the two to get to and I have the special socket and a large breaker bar on the way. I'm also getting a Butane torch to get some heat on the area if I have to. Assuming it all goes well and the fault clears I may well give the resistor fix a try as the cost will be so low. If that doesn't work I will look into changing the other sensor.

Will keep you all informed.

MUDGUTS · August 18, 2015

The sensor has arrived. Yesterday I gave the old one a quick tweek using the special socket and 45cm breaker bar and it came loose quite easily so I replaced it today.

The first thing I did with the new one (branded Walker, £72) was check the resistance of the heater circuit (pins connected to the black wires). It was 16 Ohm, so within spec as described by Colin above.

I checked again for codes, and they were both there, so I cleared them. Incidentally some fault code readers can set off the VSC & TRC lights. I found some info as below and cleared them also, see pic.

http://www.lexusownersclub.co.uk/forum/topic/84168-vsc-light/?p=837673

The new sensor came with some clips for the cable and a small sachet of copper grease. It was easy to fit.

I checked again for codes afterwards and they were BOTH gone but I would expect the code for O2 Heater Circuit Bank One, Sensor 2 (P0141) to come back on in the future, as I know that sensor heater circuit is open.

ColinBarber · August 18, 2015

Good work Phil. :)

Provided copper grease is used the sensors are normally fairly easy to undo.

MUDGUTS · August 21, 2015

As predicted the EML came back on after about 30 miles. So I checked and the fault code for the heater circuit on bank 1, sensor 2 was there.

I've fitted the second sensor today. When I checked the resistance of this one it was 16.7 Ohm.

As before I checked and cleared the single fault code first and this time I don't expect it to come back.

Hope this thread is of use to someone who passes by looking for info. Thanks again for your help, Colin.

The job is quite easy, provided you have the right tools.

Finally, shame on the local (Northampton & Daventry) garages who just couldn't be bothered to email me with a price for this job. Consequently I did it myself and proved how simple it is. They have lost income as a result.