Chris NottVolks Autos
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  1. #1
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    Join Date
    Apr 2013

    3.0TDi Lambda/Equivalence Ratio readings

    Hi all,

    I have owned my 2010 3.0TDi A6 S-Line Special Edition (auto) for just over a week. I love the car! Keep finding new toys and features on it.

    My only concern is that I notice that the MPG readings shown by the car are considerably lower than the Urban 30.1 MPG quoted by Audi. I have done a full VCDS Scan and have no fault codes showing. My daily driving is mixed between dual carriageway and lanes. I appreciate I did not purchase a 3.0TDi Quattro for fuel economy alone but was hoping to see better results from the diesel than 20-21 MPG averages.

    I scanned the car with an EOBD package and was surprised to see the B1S1 Sensor Equivalence Ratio reading was mostly sitting under 0.4. I know with petrol cars the equivalence ratio should be 1.00 and the Engine Management system fights to maintain the value at 1.00. Is this different for diesels? I logged a full drive and am getting some very strange readings for the equivalence ratio - sitting at around 0.4 then jumping to 1.99. The car has 68K miles on it and I am wondering if the lambda sensor is failing. I have attached a screenshot of my readings below:


    My engine code is: CDY0 (engine introduced in 2009 I believe).

    Should I try changing the lambda sensor?

    Thank you.

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  3. #2
    Reverse Gear

    Join Date
    Apr 2013
    Update on my previous post.....

    I took the plunge and fitted a new Lambda sensor - not a fun job and have plenty of cuts to show for it. I also removed and cleaned the MAF sensor. Disappointingly there is very little change. The sensor readings are sharper but no change to the overall Equivalance Ratio or my MPG readings. It is still centralised around the 0.3 - 0.4 mark, which baffles me as all my reading-up on this value indicate it should be showing 1.00 or near.

    I have attached my new scan below:


    Anyone with an EOBD tool or VCDS and a similar model (3.0 diesel with lambda sensor fitted)? Can you please check the Equivalence Ratio (or Lambda) reading on your car? It should be shown on VCDS if you go in under EOBD. Really keen to know if this is a normal reading for the 3.0 TDi or if I need to investigate more on my car.




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