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swapped the ECU on your Mercedes and now
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the car won't start that's the
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immobilizer kicking in your new ECU
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isn't paired with the rest of the car's
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security system yet and yeah it's not
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plugandplay like some other brands hey
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I'm Tom from Car Justify if you've
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replaced the engine control unit on a
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Benz maybe after damage water intrusion
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or a performance upgrade you're probably
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stuck with a no start and a blinking
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immobilizer light i'll walk you through
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what actually needs to happen to
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reprogram that ECU and get the car
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so first thing Mercedes ECUs are married
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to the car's immobilizer system that
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includes the ECU itself the EIS
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electronic ignition switch the key and
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the ESL electronic steering lock if
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those aren't matched the car won't crank
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there are really two main ways to
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reprogram or virginize an ECU so it can
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be paired with your vehicle one is by
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using official Mercedes diagnostic
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equipment like the Star diagnostic
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system with online access the other is
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with aftermarket tools and software
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which some independent shops or tuners
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use if you've got a used or donor ECU
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you'll need to either virginize it
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basically wipe the old vehicle data from
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its memory so it can be repaired with a
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new system or clone your original ECU
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copy all the data from your old unit
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onto the new one virginizing requires
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opening the ECU and accessing the EPROM
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chip inside you'd use a programmer like
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VVDI Autel or KAG to dump the original
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file clear the immobilizer info and
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reflash it once it's virgin you install
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it in the car and use a diagnostic tool
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to perform the initial startup procedure
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that links it to the EIS and key cloning
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is a little easier if your old ECU is
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still readable you connect both the old
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and new ECUs to the programmer and do a
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direct copy that way the new one becomes
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an exact twin of the original same
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immobilizer same VIN same everything now
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if you're using a brand new ECU straight
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from Mercedes that comes blank and is
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ready to be married to the vehicle but
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you'll still need a dealership or
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specialist with Star Diagnosis access to
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code and activate it and no just
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swapping the ECU and clearing codes
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won't get you past the immobilizer the
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car looks for that handshake between
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modules at every startup if it doesn't
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match it kills the ignition signal so
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what can you do if you're working at
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home if you're not comfortable with
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EPROM programming or don't have access
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to Star your best bet is to pull the ECU
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and send it to a professional bench
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service they can clone or virginize it
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properly and send it back ready to plug
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in once the ECU is matched start the car
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and confirm the immobilizer light goes
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out and the steering lock disengages
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quick recap mercedes ECS are security
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locked to the ignition system
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a swapped unit must be virginized or
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dealer tools or advanced programmers are
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required you cannot bypass this with a
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basic scanner or battery reset hope that
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clears things up if you're diving into
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Mercedes electronics it's not light work
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but it's doable with the right tools or
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the right help if this helped you
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understand what's going on with your
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Benz after a swap hit like and subscribe
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to Car Justify for more straight talk
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solutions from the garage see you next
