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On
W124 and W201 chassis, the relay is located
in back of the plastic cover behind the
battery. On W126 chassis it is located between
the 2 firewalls underneath the hood. On
W107 chassis it's located behind the right
kick panel.
Check
the 10 amp fuse on top of it first. If it
is blown, replace it. If it is good, check
the socket that that the fuse sits in for
corrosion. Clean and/or replace as necessary.
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| The
relays were also known to have weak solder
joints from factory and go prematurely bad,
but chances are the relay was doing its job
protecting your car's control units, and give
thanks that it did. The components it was
protecting are expensive. |
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| What
does the relay have to do with the way my
car runs? |
| The
Mercedes over voltage protection relay provides
voltage to the ABS and Mercedes engine control
units. In the case of hard start, when you
cut off the voltage supply to the engine control
unit, you loose all of your cold idle circuits.
This includes the idle and cold fuel enrichment
circuits. The fuel enrichment circuit is used
to start you engine when it is cold. The idle
circuit is used for increased rpm when the
engine is cold, and curb idle when the engine
is warmed up. When these circuits do not operate
the engine can still run, but very poorly.
Plain and simple - the control units can not
operate the systems of your car without voltage.
No voltage equals all kinds of derivability
problems. |
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| Tech
Tip: When checking voltage at the pins of
the overload protection relay pin 30 is hot
with the key on and pins 87 are the output
voltage to the control units. If the relay
is blown there will not be voltage present
at pins 87. |
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