O2 Sensor

[Amrit]

I am after an advice....My W203...started showing engine light.....When Plugged on Diagnostics it says...." O2 sensor voltage Low....Sensor 1 Bank 1" ...Could you please advise the location of this sensor.....Am I correct in quoting that W203 has only two sensors.. one pre cat and another one post cat.....Why I am confused is when I plug it on diagnostics its shows 6 ....O2 sensors

 

[ron123wdf]

Hi,
My C 240 has o2 sensors 1 on each bank lh/rh just after exhaust manifold later cars also have them fitted after the cat. have you tried a live data test you should be able to see what voltage they cycle at (between .1v lean .9v rich) .45v is the ideal reading.
Make sure you fit Mercedes or Bosch (try Ebay) as a cheep one will not work well Ive just fitted 1 (Mercedes £200 Bosch Ebay £60). It may also be a good idea to test sparkplugs coil etc as a missfire ie unburnt fuel will cause a low voltage.
Good luck
Ron

 

[Amrit]

Thanks for the advise...Link below shows values what I am getting on suspected sensor. I will replace spark plugs as well in case they are causing any problem.

Thanks

http://i14.photobucket.com/albums/a338/mramrit/test4.jpg

 

[Amrit]

is pre cat sensor different to post cat.. or are they same

 

[ron123wdf]

Ithink you will find its different, but .2v is very low on the 1st sensor did you notice if any higher readings were given at any time during the test? as the ECU will richen up the fuel supply to try and get .45v which is 14.7 to 1 the best fuel oxygen ratio.
Sensor life is 100,000 miles so if your car is past that it may pay to replace them you will find a Mercedes and Bosch number engraved on the body just above the hexagonal nut. Try this website for more information http://www.lambdapower.co.uk/Diagnosis/Diagnostic_index.asp#q11
Regards Ron

 

[Adamerc]

Ron,

Thanks for your reply....I have placed an order.

Regards

 

[nickcc101]

Had same sensor fault on my W203 C180, engine light on. Turned out to be Throttle butterfly not closing allowing overfuel which triggered both 02 sensors. Removed throttle housing, cleaned off sticky black gunge from butterfly and throttle housing, removed fault code with own scanner /reader, no problems since.

 

[Amrit]

I am back with the update on this issue......

Nickcc101 :- I have checked throttle housing and its looks clean and nice .....still I cleaned with clean cloth.....I noticed one thing though on butterfly ...it was not in fully closed position ...is this normal....?

I did couple of things last weekend on my Car ... Changed Spark plugs with new NGK Iridum plugs...as have read on website these are best and will last longer...
Checked Air filter which looks ok... hence not changed ..just cleaned it with Vaccum Cleaner...

Now about O2 sensor... Yes I received O2 sensor by post of NGK which I replaced .....One thing I noticed which I dont think was right ...is connector coming from CAR was wet in oil... wire was all dry by connector inside was wet with oil...Don't know where it came from .....Welll I sensor with new one.....

Previously I was getting two messages P0131 & P0171 ...after replacing Sensor Diagnostic system has started showing P0135 ( Sensor heater Circuit Malfunction)...I am not sure why that happened ..

I have made my own two theories of this issue

1) Sensor is faulty
2) May be as I changed the sensor to new one ECU may have registered that sensor is missing hence gave me the message.

Moving Forward I have gone with option two and have cleared the codes...so far I have driven car nearly 35 miles and have not seen engine light coming back on.

Readings which I am seeing on diagnostic for O2 sensor are ( they are not consistent and are fluctuating going up & down )

Reading One

Sensor one Bank One 0.43
Sensor one Banck Two 0.435

Reading Two

Sensor one Bank One 0.89
Sensor one Banck Two 0.795

Reading Three

Sensor one Bank One 0.775
Sensor one Banck Two 0.765

Reading Four

Sensor one Bank One 0.61
Sensor one Banck Two 0.72

Reading Five

Sensor one Bank One 0.755
Sensor one Banck Two 0.705

Reading Six

Sensor one Bank One 0.8
Sensor one Banck Two 0.715

Reading seven

Sensor one Bank One 0.8
Sensor one Banck Two 0.72

Reading Eight

Sensor one Bank One 0.79
Sensor one Banck Two 0.69

Below mentioned readings are after I drove Car for around 9 miles....Engine must have been hot by then

Reading One

Sensor one Bank One 0.09
Sensor one Banck Two 0.81

Reading Two

Sensor one Bank One 0.835
Sensor one Banck Two 0.765

Reading Three

Sensor one Bank One 0.8
Sensor one Banck Two 0.84

Could someone please help and confirm If sensor is working fine after reviewing readings above ....or do I need to get another sensor from Company where I bought it from...Though they are shipping another sensor today for my attention ..I dont really want to change it if above readings are of a healthy sensor.

Thanks in advance

 

[Adamerc]

I don't think anyone on this forum can advice you with these readings if your sensor is performing as per spec. You might have to look somewhere else. Check Google search

 

[BlackC55]

You dont; have a second bank so ignore those values.

You need to see fluctuating Mv values for the pre cat lamda probe while running. They must be whithin spec. (roughly 80-800Mv)

You really need to plug it into better diag machine such as a Star.

 

[nickcc101]

No the butterfly won't close fully. Presume works same as carb and stays partly open to allow engine to tickover.