E34 520i M50B20 Overfuelling! O2 sensor heater relay?
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    E34 520i M50B20 Overfuelling! O2 sensor heater relay?

    Ok now some of you may or may not know that I have an over-fuelling issue with my E34 520.

    So today I went to see my mate and got the codes read, the scanner said that the was a problem with the O2 sensor heater relay.

    So upon further investigation we discovered that there is no O2 sensor heater relay!

    It should be where the arrow indicates according to the bentley manual!!



    As you can see the relay isn't there and there is no wiring at all going to that position!

    How can this be?

    Now I can understand the code coming up if the relay was missing, but surely the car should have one!

    Any help with this would be greatly appreciated as I really need to get this sorted as the smell of excess fuel is getting to me now! lol


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    Just got online Kev and pm sent

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    Last edited by watty; 23-07-2012 at 23:25.

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    Cataclysm (24-07-2012)

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    Best thing to do is find what pin from the ecu works the sensor heater, then you will have the correct wire colours to work back from...

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    Cataclysm (24-07-2012)

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    Cheers guys!
    Having delved a little deeper, it turns out that my car and the majority of 520's with the M50B20 engine were fitted with the Siemens MS40 ECU instead of the Bosch one fitted to the M50B25, so that is why there is no relay!
    According to the wiring diagram that I have found the sensor is wired directly to the ECU and there is no relay! Which would explain why it is missing!
    So therefore it would stand to reason that it is the heating element in the sensor that is at fault, so I managed to find an eBay seller selling an NGK sensor for only 67! Which is more expensive than the Bosch equivalent, still never mind, hopefully this will cure the problem, and I won't be fuming out the guys following behind anymore! Lol


    Despite the high cost of living, It remains popular!

    Never bullshit a bullshitter, they'll just bring you down to their level and trash you with experience!

    A mate of mine recently admitted that he was a brake fluid addict! When I quizzed him about it he insisted that he could stop any time.

  7. The Following 2 Users Say Thank You to Cataclysm For This Useful Post:

    Steve (24-07-2012),watty (25-07-2012)

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