TECH - Coolant Level Warning Circuit

[ranahan@charter.net (John Erickson)]

My problems were concurrent with yours.   Your relay suggestion got me 
scanning the archives and digging through the Bentley.  My problem ended up 
being the connector on the sensor.  It wasn't until I completely 
disassembled it, cleaned it with Deoxit and crimped the connectors a little 
that I eliminated my problem.

John

At 07:00 AM 8/24/2002 -0700, Larry wrote:
>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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