the_IT_bloke
Past Member
I am having similar issues with out of band mixtures (Fault codes 16804, 17560, 17912 thread in Diagnostics forum) with my 1.6FSi petrol engine.
There seem to be many posters with similar issues.
The problem is that the management system makes a decision to set mixture based on a number of sensors MAF, MAP Oxygen, NOX, temperatures etc.
The system selects a short term mixture setting based on immediate dirving style/conditions and selects a long term setting based on an average of conditions.
The management system then acts on these settings by adjusting ignition timing, pulse width of injectors, EGR, airflow etc.
Because all these are linked the issues could be with any point (including the infamous air leak). Also, although total sensor failures may be detected, drifting or failing sensors may cause the mixture to be adjusted further out until the light comes on over time (long term trim settings) after 1-2 hours driving.
Resetting the fault light also clears the 'learned settings' so the light goes out. Over 1-2 hours driving the engine re-learns the settings / compensations and the engine light comes back on. Resetting codes and clearing the engine ligh does not fix the underlying issue, it just masks it.
None of these statements help solve the issue, but does explain why the independants (and mainy dealers) randomly change components as they dont have a stock of parts to swap out until they fix it, also its only 'slightly out' so you have to do some driving for the issue to manifest its self....
Top three quoted suspects;
1) Air leak - cheap to fix - rearely identified (some on this website)
2) MAF - £80-£100 reconditioned unit from Audi
3) Lambda - I was quoted £150 from Audi - much cheaper units availble but quality / reliability not as good?
Unfortunately people rarely go back into forums to detail what actually fixed the issue so many posts just end with no resolution - please post your fixes when you get them...
Regards and Good Luck
Paul
There seem to be many posters with similar issues.
The problem is that the management system makes a decision to set mixture based on a number of sensors MAF, MAP Oxygen, NOX, temperatures etc.
The system selects a short term mixture setting based on immediate dirving style/conditions and selects a long term setting based on an average of conditions.
The management system then acts on these settings by adjusting ignition timing, pulse width of injectors, EGR, airflow etc.
Because all these are linked the issues could be with any point (including the infamous air leak). Also, although total sensor failures may be detected, drifting or failing sensors may cause the mixture to be adjusted further out until the light comes on over time (long term trim settings) after 1-2 hours driving.
Resetting the fault light also clears the 'learned settings' so the light goes out. Over 1-2 hours driving the engine re-learns the settings / compensations and the engine light comes back on. Resetting codes and clearing the engine ligh does not fix the underlying issue, it just masks it.
None of these statements help solve the issue, but does explain why the independants (and mainy dealers) randomly change components as they dont have a stock of parts to swap out until they fix it, also its only 'slightly out' so you have to do some driving for the issue to manifest its self....
Top three quoted suspects;
1) Air leak - cheap to fix - rearely identified (some on this website)
2) MAF - £80-£100 reconditioned unit from Audi
3) Lambda - I was quoted £150 from Audi - much cheaper units availble but quality / reliability not as good?
Unfortunately people rarely go back into forums to detail what actually fixed the issue so many posts just end with no resolution - please post your fixes when you get them...
Regards and Good Luck
Paul
