High emission values at the MFK: particulate filter or lambda sensor?

Hello everyone, During my last vehicle inspection (MFK), my BMW X3 was flagged due to excessively high exhaust emissions. The measured value was 1,034,000, while the target value is 250,000. My workshop recommended replacing the particulate filter, as it might be clogged. However, my vehicle doesn't show any typical symptoms like a lit engine warning light, reduced engine power, or increased fuel consumption. The following error messages were displayed when the fault memory was read: - Error code 287500: Lambda sensor before catalytic converter – signal too low during overrun - Error code 287100: Lambda sensor before catalytic converter – signal too high during partial load I want to make sure the cause is correctly identified before replacing any parts. How can I check the function of the particulate filter and the lambda sensor? Would it be advisable to replace the lambda sensor, or could another problem be causing the increased exhaust emissions? I would be very grateful for your expert assessment and recommendations. Thank you in advance!

(Translated from German)

9 comment(s)

Start by checking the lambda sensor connections and wiring for any visible damage or loose connections, as these can affect sensor readings. If everything looks fine, consider cleaning the lambda sensor to see if it improves the readings. If the issue persists, it might be worth replacing the lambda sensor before moving on to more costly repairs like the particulate filter. Keep an eye on any changes in performance or emissions after these checks. Let me know how it goes or if you have further questions!

Quotation:
@CarlyMechanic wrote on
Start by checking the lambda sensor connections and wiring for any visible damage or loose connections, as these can affect sensor readings. If everything looks fine, consider cleaning the lambda sensor to see if it improves the readings. If the issue persists, it might be worth replacing the lambda sensor before moving on to more costly repairs like the particulate filter. Keep an eye on any changes in performance or emissions after these checks. Let me know how it goes or if you have further questions!

I did a forced regeneration today and will have the exhaust gas values measured again tomorrow. Otherwise, as you said, I will check and clean the lines. I will continue to report.

(Translated from German)

Quotation:
@Gökhan wrote on
I did a forced regeneration today and will have the exhaust gas values measured again tomorrow. Otherwise, as you said, I will check and clean the lines. I will continue to report.

Great, performing a forced regeneration is a good step. After checking the exhaust gas values, if the issue persists, inspect the lambda sensor connections and clean them as planned. Keep us updated on the results, and feel free to ask if you have any further questions!

Quotation:
@CarlyMechanic wrote on
Great, performing a forced regeneration is a good step. After checking the exhaust gas values, if the issue persists, inspect the lambda sensor connections and clean them as planned. Keep us updated on the results, and feel free to ask if you have any further questions!

On Saturday, I performed a forced regeneration with Carly Software and measured the values again today. The result was impressive: The soot load has dropped from 1034.5 k#/cm³ to 9.7 k#/cm³. Regarding the lambda sensor, I'm still unsure whether a replacement is necessary, as the error persists when reading out the data. I will examine this more closely. Thank you for your helpful information!

(Translated from German)

Quotation:
@Gökhan wrote on
On Saturday, I performed a forced regeneration with Carly Software and measured the values again today. The result was impressive: The soot load has dropped from 1034.5 k#/cm³ to 9.7 k#/cm³. Regarding the lambda sensor, I'm still unsure whether a replacement is necessary, as the error persists when reading out the data. I will examine this more closely. Thank you for your helpful information!

If the error persists, try swapping the lambda sensor with a known good one if possible, to see if the error clears. This can help determine if the sensor itself is faulty. Keep us posted on your findings, and let me know if you have any more questions!

Quotation:
@CarlyMechanic wrote on
If the error persists, try swapping the lambda sensor with a known good one if possible, to see if the error clears. This can help determine if the sensor itself is faulty. Keep us posted on your findings, and let me know if you have any more questions!

That will take a while until I can check it and replace it. My workshop recommends replacing it anyway between 100,000 and 120,000 kilometers, whether it's broken or not, because it's a wear part. What do you think?

(Translated from German)

Quotation:
@Gökhan wrote on
That will take a while until I can check it and replace it. My workshop recommends replacing it anyway between 100,000 and 120,000 kilometers, whether it's broken or not, because it's a wear part. What do you think?

Replacing the lambda sensor as a preventive measure between 100,000 and 120,000 kilometers is a common practice, as it can degrade over time and affect performance and emissions. If you're nearing that mileage and still experiencing issues, it might be wise to replace it. Let me know if you have any further questions!

Quotation:
@CarlyMechanic wrote on
Replacing the lambda sensor as a preventive measure between 100,000 and 120,000 kilometers is a common practice, as it can degrade over time and affect performance and emissions. If you're nearing that mileage and still experiencing issues, it might be wise to replace it. Let me know if you have any further questions!

Today I went back to the MFK (vehicle inspection) hoping that the exhaust emission values would be okay, but unfortunately they were too high again: 700,000#/cm3. Last week, after the forced regeneration, they were only 9,000#/cm3. I only drove twice in a week and the values are already so high. What could be the cause? First, I'll try a chemical additive in the DPF to clean it. What do you think about that?

(Translated from German)

Quotation:
@Gökhan wrote on
Today I went back to the MFK (vehicle inspection) hoping that the exhaust emission values would be okay, but unfortunately they were too high again: 700,000#/cm3. Last week, after the forced regeneration, they were only 9,000#/cm3. I only drove twice in a week and the values are already so high. What could be the cause? First, I'll try a chemical additive in the DPF to clean it. What do you think about that?

Using a chemical additive to clean the DPF can be a helpful step, especially if the filter is partially clogged. Make sure to follow the product instructions carefully. If the problem persists, it might be worth investigating potential issues with the engine that could be causing excessive soot production, such as faulty injectors or turbocharger problems. Keep us updated on the results, and feel free to ask if you have more questions!

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