[xj40] False readings on coolant and brake fluid


(Alan4d) #1

I keep getting false warning messages ‘brake fluid low’
and ‘coolant low’ and find that they are not. Anyone actually had
this problem and how did you fix it?–
Alan (XJ40 3.6L 1987/8)
Salamander Bay, nr Newcastle, Australia
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(Jaguarpete) #2

In reply to a message from Alan4d sent Sun 28 Apr 2013:

I gave up on the coolant sensor on my 88. The float has a
magnet in it which opens and closes a reed switch in the
housing. Over tine, the plastic around the magnet cracks
and rust accumulates and that interferes with the accuracy
of the switch, which alarms when the circuit is open. I
finally shorted out the two pins in the plug to make the VCM
happy. I think the float in the brake reservoir works the
same way, but I haven’t had a failure with that one yet.
You can pull the switch and float out of the coolant
reservoir. The collar at the end of the reservoir is
threaded.–
The original message included these comments:

I keep getting false warning messages ‘brake fluid low’
and ‘coolant low’ and find that they are not. Anyone actually had
this problem and how did you fix it?


Pete Peterson 70E(193K) XJ40s(88-270K,89-97K, 94-122K)
Severna Park, Maryland, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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(Alan4d) #3

In reply to a message from Jaguarpete sent Sun 28 Apr 2013:

Yes, and I stripped an old one down. As well as the magnet and the
reed switch there is an embedded resistor, the idea being that if
you have a completely open circuit (like a broken wire) that will
also signal a problem. Trouble is I’ve forgotten the value of the
resistor. But I’m loath to fudge the OK signal. What happens if a
there’s a losse care plug or if a hose bursts? I don’t want to wait
until steam comes out of the bonnet. Steam coming from my ears is
bad enough!–
Alan (XJ40 3.6L 1987/8)
Salamander Bay, nr Newcastle, Australia
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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(Jaguarpete) #4

In reply to a message from Alan4d sent Sun 28 Apr 2013:

The wiring diagram show a resistor in series with the reed
switch. I jumpered my level switch at the round black
connector leading to the switch, and the VCM appears to be
happy. My parts book has the level switch as DBC 2111.
Maybe the usuals will still have it available.–
The original message included these comments:

Yes, and I stripped an old one down. As well as the magnet and the
reed switch there is an embedded resistor, the idea being that if
you have a completely open circuit (like a broken wire) that will
also signal a problem. Trouble is I’ve forgotten the value of the
resistor. But I’m loath to fudge the OK signal. What happens if a
there’s a losse care plug or if a hose bursts? I don’t want to wait
until steam comes out of the bonnet. Steam coming from my ears is
bad enough!


Pete Peterson 70E(193K) XJ40s(88-270K,89-97K, 94-122K)
Severna Park, Maryland, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !


(Alan4d) #5

I just want to add to this old thread. I recently managed to source a brand new brake fluid level sensor and fitted it, only to still have the warning message! Then it clicked! The message is not extinguished when the fluid is topped up to or slightly about minimum, where I always used to keep it. Nor is it meant to be! When the fluid is topped up to just below maximum all is fine!