System Malfunction Alarm

[pheobe]

Hi.

I had an alarm come up checked the code and it came up as O2 sensor heater circuit malfunction, It has reset with the code reader and did'nt come back on when engine was started I have'nt give it a run yet. I have no idea of what this is or what it does or if it's going to stop me part way through a trip. Any help or advice would be most welcome.

Thanks in advance Eric

[steve2006]

It means one of the Lambda or O2 sensors has a fault either with the sensor itself in this case the heater circuit or the wiring to it.

To work properly the sensor needs to be heated up so when the engine is cold it is warmed up quickly by an internal heater a bit like an immersion heater warms up the water in your tank.

The OBDII code will normally tell you which bank it is on ( driver's or passenger side as this is a V8 engine) and whether it is before the catalytic convertor ( pre cat) or after it (post cat).

These sensors measure the exhaust emissions and adjust the amount of fuel being injected for optimum performance.

I would wait and see if the warning light reappears and then read the codes again if it does.

You can continue to use the car with this fault although it may go into Limp Home Mode with reduced performance to protect the engine and it may increase fuel consumption as the computer will use default settings for fueling instead of live data from the sensor. Put it this way you won't break down.

If you want to read more the link below explains the basics.

http://www.aa1car.com/library/o2sensor.htm

[pheobe]

Hi Steve Thanks for that good info, got a 500 mile trip on Thur so we will see what happens. I have the fault code as po155 which should be bank 2 sensor 1, I have looked at the parts locator dia: and it's not easy to figure out exactly were this thing is but it appears to be on the near side and the o2 sensor nearest the front of the vehicle.

Thanks again for the reply Eric

[ColinBarber]

normally the heater element within the sensor burns out which means it is quite rare to get a false or temp. error code relating to the heater circuit. Therefore expect to get your warning light on again soon. It doesn't come on immediately because the ECU uses two-trip logic meaning it has to see the fault twice so you have to go through two heat cycles and two complete ignition on/off sequences before the error will come up again.

B2S1 is the first sensor (upstream on the main cat) on Bank 2 which is the right bank when sitting in the car and looking forwards (off side for a RHD vehicle)

[pheobe]

Hi Colin thanks for that, read a bit more re 02 sensor still not sure exactly were it's located but i'm sure i'll find it when I start looking, what i've read confirms what you have already told me, but the more you read the more it seems that it could be more than just a lambda sensor but i'll have start with something, never changed one before is there anything that may crop up, and is there any problems with after market sensors any advice would be more than welcome.

thank you for the info Eric

[ColinBarber]

the sensors on the 4.3 V8 are standard O2 sensors rather than air/fuel ratio sensors which means they are somewhat cheap. I would however only use a Denso sensor rather than a really cheap alternative.

Either a Lexus part from a dealer or a Denso aftermarket specifically for the engine (OEM). Unfortunately Denso in Europe don't do an aftermarket so you would have to import from the US from somebody like Rock Auto.

I believe the part required is Denso 234-4630 and would be around £60 imported. Rock Auto are very good, you can pay import duties up front so you don't have to pay handling fees at the UK end and it would normally be delivered within a few days.

The sensor is located on the downpipes from the engine. You would get at it from under the vehicle once you remove the plastic underguards.

It is very unlikely to be anything other than the sensor - potentially a wiring issue or 1 in a million chance of an ECU issue. With your vehicle being a 2003 model that is about the time I would expect to see these sensors fail.

[pheobe]

Hi Colin thanks for your time and info feel much more confident i'll let you know how I get on

Thanks again Eric

[Maduggo]

the sensors on the 4.3 V8 are standard O2 sensors rather than air/fuel ratio sensors which means they are somewhat cheap. I would however only use a Denso sensor rather than a really cheap alternative.

Either a Lexus part from a dealer or a Denso aftermarket specifically for the engine (OEM). Unfortunately Denso in Europe don't do an aftermarket so you would have to import from the US from somebody like Rock Auto.

I believe the part required is Denso 234-4630 and would be around £60 imported. Rock Auto are very good, you can pay import duties up front so you don't have to pay handling fees at the UK end and it would normally be delivered within a few days.

The sensor is located on the downpipes from the engine. You would get at it from under the vehicle once you remove the plastic underguards.

It is very unlikely to be anything other than the sensor - potentially a wiring issue or 1 in a million chance of an ECU issue. With your vehicle being a 2003 model that is about the time I would expect to see these sensors fail.

I think with Colin's description of location and this image you should find the beast in question

O2 sensor.pdf

[ColinBarber]

it will probably be difficult to get an open spanner on the sensor so you will need an O2 socket, maybe an offset one like the following:

http://www.ebay.co.uk/itm/OXYGEN-SENSOR-SOCKETS-LAMBDA-SENSOR-REMOVAL-FITTING-SOCKETS-22mm-/320949749664?pt=UK_Hand_Tools_Equipment&hash=item4aba1887a0

[pheobe]

Hi thanks to all who responded to my post.

A quick up-date I have ordered new sensor, got he old one out to-day I borrowed the lambda socket but it started to slip so I did away with that idea and loosened the heat shield that allowed me to get a ring spanner over the elec plug and onto sensor and off it came. Hopefully this will clear the fault. I will let you know the outcome.

regards Eric

[pheobe]

Hi All

New sensor came to-day fitted and run motor around the block all seems well.

Many thanks to all who helped with info and to those who had already made info available a great help.

Regards Eric

[ColinBarber]

Excellent Eric. You will probably need to take it on a couple more runs to be 100% sure but it sounds like the issue is resolved :)

Where did you get the new sensor from in the end?

[Maduggo]

Good fix I hope, saved you a few hundred £ at Lexus.

Well done