Yup you are correct that light stays on for the earlier models according to a few posts here, mine goes off after 17mins in my 2004 3.0d.....do an amp draw tests see what the readings are with the fsu in and and then take it out and do test again....set the multimeter to amp mode and see what reading you get

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E53 X5 3.0d SUV prod.date 11/2004 eng.variant M57N Europe Right hand drive N