TECH - Coolant Level Warning Circuit

[Larry" <rocco16v@netzero.com (Larry)]

It only fixed the problem because the problem was bad connection, not
polarity.
John-  why couldn't you have given this great run-down a month ago when I
was begging for suggestions on why my light was flashing??????!!!  (it
turned out to be the 'relay')  You would have saved me weeks of
frustration....:)

Larry


> great write up.  I would add that the connector to the temp sensor is not
a one
> way connector.  I chased a blinking coolant light for 3 weeks and found
the
> connector was plugged in backwards.  Turning it over fixed the problem.
>
>
> --- John Erickson <ranahan@charter.net> wrote:
> > Flashing Low Coolant Light Circuit Description.
> >
> > The trigger for the warning circuit is the sensor in the
> > top of the coolant expansion tank.  Make sure you have the
> > proper level of coolant and the electrical connection on
> > top is clean.  Assuming that there is electrical
> > continuity everywhere in the circuit (no broken wires or
> > dirty electrical connections), there can only be two
> > things that cause the light to flash when there is the
> > proper amount of coolant in the expansion tank: a faulty
> > sensor and/or relay.
> >
> > If you look at the sensor, it consists of two small metal
> > rods (probes) that extend into the coolant.  If current
> > can't pass between the probes (low coolant condition),
> > then the relay will activate the warning light in the
> > temperature gauge.  I really don't know how the sensor
> > could fail, but perhaps if the cooling system was
> > neglected for a very long time, corrosion might be an
> > issue or perhaps there might be a build up of crud on the
> > probes inhibiting current flow.  You can remove the sensor
> > and clean off the probes.  You can also test it via a
> > simple continuity check (probe-to-connector).  New sensors
> > cost US$10.
> >
> > The relay is in position #18: third row (top) far right
> > hand side. There is a "43" on the old relays (new ones are
> > blank).  Its only function is to pass current through the
> > sensor and to trigger the light if it can't.  Its not a
> > standard electro-mechanical relay, by the way.  You cannot
> > take it apart and clean any contacts.  It has a small
> > printed circuit board inside with some sort of silicone
> > device (chip) on it, a few resistors and perhaps a diode
> > or two.  I'm pretty sure its an electronic relay, but it
> > may be slightly more complicated than that.  If you remove
> > the relay, you will still get the flashing coolant level
> > light when you start the car.  That's a bulb test function
> > not associated with the relay or the sensor.  New relays
> > cost US$30.
> >
> > Continuity issues:  Before you start replacing parts,
> > clean the relay contacts and the connector on the sensor.
> >   The connector on the sensor is terribly susceptible to
> > corrosion due occasional baths in coolant.  The connection
> > also tends to get loose from frequent use.  If you spend
> > much time in that corner of the engine compartment, the
> > expansion tank gets moved a lot.  As a result, the
> > connector gets yanked a lot.
> >
> > There is very little information about the low coolant
> > warning light in the Bentley manual.  The circuit is not
> > covered in the electrical schematics.  I found the relay
> > in the manual, but, according to the book, my car doesn't
> > have one.  It's called the "low coolant indicator/idle
> > boost control relay."  Perhaps on some cars it's the low
> > coolant indicator relay and on others it's the idle boost
> > control relay.
> >
> >
> > _______________________________________________
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> > Scirocco-l@scirocco.org
> > http://neubayern.net/mailman/listinfo/scirocco-l
>
>
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