Pre-Cat Oxygen Sensor failure symptoms

[hgg]

Hi,

I am getting the following OBD2 codes for quite some time now:

P0170 Fuel Trim Bank 1
P0130 O2 Sensor Circuit B1S1
P0135 O2 Sensor Heater B1S1

The pre catalytic converter oxygen sensor has failed I guess.

The fuel consumption has not changed at all, all these months.
It also passed MOT fuel emissions without any issues.
The only thing I have noticed is that when you step on the gas suddenly
from idle, the engine does not rev as fast as it used to and sometimes the idle
is a bit rough.

From what I read, in case of a defective O2 sensor the engine is using some
predefined values.

Are the above the symptoms of a failed O2 sensor?
Thanks.

 

[colb]

Fuel trim code may be down to a vacuum system air leak, check all rubber and plastic hoses and intake boots for holes or splits, replace any that are found. A good diagnostic scanner that can look at live data will display what the fuel trims are doing if they are high then its probably due to air leaks, the increased unmetered air that gets in from leaks has nor been measured by the Maf sensor in the intake and the exhaust sensors pick up the unmeasured air in the exhaust. The engine management then sees this as a lean mixture and will command more fuel to be injected to richen the mixture. The exhaust sensor codes you have would indicate the pre cat sensors are duff, again in live data you should be able top view what they are performing like, working sensors should produce a wave form graph as their voltage rises and falls. A bad sensor will either be static or be very slow to react. If you view post cat sensors they usually look quite static unless they are reacting to emissions in the exhaust fumes.
You will find some good videos on Youtube that explain fuel trims and exhaust sensors in more detail.
If the exhaust sensors are duff and fuel trims out of whack then you were lucky to get it through the MOT.

 

[hgg]

Fuel trim code may be down to a vacuum system air leak, check all rubber and plastic hoses and intake boots for holes or splits, replace any that are found. .

Thank you for the detailed explanation.

Does this count as a vacuum leak to trigger the P0170 Fuel Trim error?
I cannot find any other cracks, splits or holes on the hoses.

 

[Andyboy]

Yes.

M54's and M43 TU engines are super sensitive to air leaks.

That's the vacuum hose to the fuel pressure regulator (the metal spaceship thing) and it won't work properly hence poor running. The black/white plastic capsule is for the air pump/emissions crap - not as important as the fuel pressure regulator. For now just run a vacuum hose direct from the manifold to the regulator until you can fit a new T piece.

 

[hgg]

Great, I have just fitted a 4mm generic one I had. The original was a black one.
I am not sure what temperatures it will experience, the one I just fitted is rated for 80 degC.

Do you think that leaving the faulty O2 sensor is a bad idea;
They are quite expensive...
Thank you for your help!

 

[colb]

As stated its a vacuum leak, check all other hoses and the inlet boot for holes or splits replace any that you find. As to exhaust sensors, the pre cat ones are quite important to ensure correct running of your engine. If it was just a code in relation to the sensors heating circuit you might get away without changing it but any other code I would suggest the sensor is duff and would replace it. Expensive, yes but its an essential part of the cars electronic system. Don't skimp on cheap pattern sensors go for Bosch to be assured that they work correctly out of the box. Cheap pattern ones are really not worth the risk.

 

[hgg]

As stated its a vacuum leak, check all other hoses and the inlet boot for holes or splits replace any that you find. As to exhaust sensors, the pre cat ones are quite important to ensure correct running of your engine. If it was just a code in relation to the sensors heating circuit you might get away without changing it but any other code I would suggest the sensor is duff and would replace it. Expensive, yes but its an essential part of the cars electronic system. Don't skimp on cheap pattern sensors go for Bosch to be assured that they work correctly out of the box. Cheap pattern ones are really not worth the risk.

Ok, I will replace it. I will try to replace it myself, although I've heard that they might be
a PITA to remove the old one...
I am curious to see if the small hesitation from idle will be corrected.
Thank you!

p.s. Are there any quantitative measurements I can take that will actually
show a better engine operation after the O2 replacement?
I only have an OBD2 scanner that can display O2, MAF and Trim readings.

 

[colb]

In live data on your scanner you should view the pre cat lambda sensor, the voltage should range up and down once the car is at operating temperature, in a graph view you should see this as a nice steady wave form as it ranges through the voltages. The post cat sensors when viewed usually look pretty static unless its picking up high content exhaust gas. Same for Fuel trims viewed on a scanner you will see if they bare high or low, you are aiming to see O% - 5% as a guide.
Maf when viewed will show gramms per second just ensure it reacts with increase in RPM's, they don't always set codes if they are faulty, if replaced only use oem Bosch or Seimens brands nothing else.

 

[hgg]

In live data on your scanner you should view the pre cat lambda sensor, the voltage should range up and down once the car is at operating temperature, in a graph view you should see this as a nice steady wave form as it ranges through the voltages. The post cat sensors when viewed usually look pretty static unless its picking up high content exhaust gas. Same for Fuel trims viewed on a scanner you will see if they bare high or low, you are aiming to see O% - 5% as a guide.
Maf when viewed will show gramms per second just ensure it reacts with increase in RPM's, they don't always set codes if they are faulty, if replaced only use oem Bosch or Seimens brands nothing else.

Thanks, I will save both the before and after data to see what will change.
The car is already more responsive after replacing that plastic connector!

 

[hgg]

The car is working fine and I am not sure if the oxygen sensor is 100% faulty. (?)
Have a look at the live data with the engine at operating temperature.
After erasing the fault codes I only got the P0130 again.

 

[t-tony]

The car is working fine and I am not sure if the oxygen sensor is 100% faulty. (?)
Have a look at the live data with the engine at operating temperature.
After erasing the fault codes I only got the P0130 again.

Go to your MOT station and ask them to do an emission test with a print out. They may do it for nothing or a few £. Turn up with the car at working temperature though to save time.

Tony.

 

[hgg]

This is from September 2023:

​	CO(%)​	HC(ppm)​	λ​
Idle​	0.00​	23​
High RPM​	0.01​	14​	0.999​

Does it compute.. ???

 

[t-tony]

Yes, that looks good.

Tony.

 

[hgg]

So, I am not sure if I still need to replace the O2 sensor despite the fault code...

 

[t-tony]

Have you cleared the fault code? If you have, has it returned?

Tony.

 

[hgg]

Have you cleared the fault code? If you have, has it returned?

Tony.

I have cleared all three codes and only the P0130 has returned.

 

[t-tony]

In that case I would get an emissions test done so you know if it has altered since the MOT. If it has I would change the sensor.

Tony.