How many O2 sensors does my car have?

[B160 Petrol]

I have a Mercedes B Class W245 B160 petrol automatic. I’m have really bad fuel economy, 17.5 MPG local city driving.

I have change the following:

1. Spark plugs
2. Air Fliter
3. Brand new Band B fuel efficiency tyres.
4. Use RON 99 fuel from Costco

I’ve read online that the O2 sensors would be the next best place to look. I have connected a ODBII reader and it looks like the car has 2 but I’m not sure. The first O2 sensor starts at around 0.435 and fluctuates when I rev the engine however the 2nd O2 sensor only fluctuates from 0.415 to 0.420 when I rev the engine.

This was a cold start and I only had the engine started for a few minutes.

Is this a problem? Would this have an issue with MPG.

By the way there is no engine management light or any message on the dash or the OBDII reader.

Thank you in advance for looking at my post.

 

[merc85]

You will have 2 Sensor's

1 Before the cat, and 1, after the cat

Air flow meter would also cause poor mpg

Front

Rear

They are both the same sensor

NGK part number , OZA683-EE20

 

[B160 Petrol]

You will have 2 Sensor's

1 Before the cat, and 1, after the cat

Air flow meter would also cause poor mpg

Front

Rear

They are both the same sensor

NGK part number , OZA683-EE20

Thank you for the reply, do the O2 sensor readings look normal to you?

Would an OBDII pick up a Air Flow Meter issue? Are there any other tell tail signs that the AFM is faulty?

Thank you once again

 

[merc85]

I'm sorry i cant help on the reading's im afraid Airflow Meter's can deteriorate before throwing a fault cold.

Dont forget from cold the vehicle will be running Rich /on choke so mpg will be poor before it warms up.

 

[Petrol Pete]

17.5 mpg !! I would be upset if my car used fuel like that, and mine is a 5.4 litre V8 !
Not sure what's wrong with your car but I hope someone on here helps you find the answer.
Good luck

 

[grober]

This may be engine temperature related. When the engine temperature is cold the injection system will run in open loop mode [ this means it ignores the O2 sensor readings which effectively fine tune/ lean out the air/fuel ratio under certain engine running conditions to improve economy] If the engine is taking along time to warm up then you are effectively "running with the choke out" to use an old carburettor term- all the time as the injection system is not switching to closed loop mode for better fuelling control. Other possibilities are failed lambda sensors as you have said or a failed MAF [ MASS AIR FLOW] metering device- on the first A/B class these came as an assembly with the engine ECU irrc, but think they can be be repaired by replacing the element if this is the case?

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more lambda sensor explanations What often fails on these is the heater element designed to bring them up to operating temperature quickly. This heater supply will be fused so worth checking any supply fuse
Short answer to why two sensors pre and post cat that the pre-cat sensor is the one used to adjust fueling and post-cat is there to monitor the efficiency of the cat.
Lambda control under closed and open loop conditions

 

[Colterry]

I would 1st look at MAF / MASS AIR FLOW.
17.5MPG I would insure it and burn it if I had that MPG. lol

 

[B160 Petrol]

I would 1st look at MAF / MASS AIR FLOW.
17.5MPG I would insure it and burn it if I had that MPG. lol

Lol

Does anyone know of any decent garages in Birmingham? Or any specialist in regards to looking at MAF?

 

[B160 Petrol]

T

17.5 mpg !! I would be upset if my car used fuel like that, and mine is a 5.4 litre V8 !
Not sure what's wrong with your car but I hope someone on here helps you find the answer.
Good luck

hanks I hope so too

 

[merc85]

MSL Birmingham

 

[MercedesDriver]

I’ve read online that the O2 sensors would be the next best place to look. I have connected a ODBII reader and it looks like the car has 2 but I’m not sure. The first O2 sensor starts at around 0.435 and fluctuates when I rev the engine however the 2nd O2 sensor only fluctuates from 0.415 to 0.420 when I rev the engine.

This was a cold start and I only had the engine started for a few minutes.

Is this a problem? Would this have an issue with MPG.

By the way there is no engine management light or any message on the dash or the OBDII reader.

Thank you in advance for looking at my post.

O2 sensor readings looks right to me, something else is causing the rich mix. Faulty MAF, injectors,...
Does the engine works smooth or hard, are there any other symptoms except bad mpg?

 

[B160 Petrol]

This may be engine temperature related. When the engine temperature is cold the injection system will run in open loop mode [ this means it ignores the O2 sensor readings which effectively fine tune/ lean out the air/fuel ratio under certain engine running conditions to improve economy] If the engine is taking along time to warm up then you are effectively "running with the choke out" to use an old carburettor term- all the time as the injection system is not switching to closed loop mode for better fuelling control. Other possibilities are failed lambda sensors as you have said or a failed MAF [ MASS AIR FLOW] metering device- on the first A/B class these came as an assembly with the engine ECU irrc, but think they can be be repaired by replacing the element if this is the case?

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For more detailed information, see our cookies page.

Accept third party cookies

more lambda sensor explanations What often fails on these is the heater element designed to bring them up to operating temperature quickly. This heater supply will be fused so worth checking any supply fuse
Short answer to why two sensors pre and post cat that the pre-cat sensor is the one used to adjust fueling and post-cat is there to monitor the efficiency of the cat.
Lambda control under closed and open loop conditions

Thank you for the reply

The car warms up normally, not noticed it take ages to warm up, I think it does look like I will need to get this looked at, I’ve only have the car since October and my previous car was a Honda jazz giving me 45MPG.

With the MAF show up on a diagnostic computer?

 

[B160 Petrol]

O2 sensor readings looks right to me, something else is causing the rich mix. Faulty MAF, injectors,...
Does the engine works smooth or hard, are there any other symptoms except bad mpg?

The engine is smooth, no smokey exhaust, no rattles, nothing else apart from really bad MPG, the has full main dealer service history.

 

[B160 Petrol]

MSL Birmingham

Thank you I will look into MSL