My low coolant warning light was not working so I decided that it was time to fix it.
Problem was traced back to low coolant warning module which was faulty. Module is located next to passenger-side fuse box. Black round plastic box with four wires going to it.
When module is disconnected you can check the operation of the warning light in dashboard by grounding White/blue wire with ignition on.
Box is sealed, but can be opened with a sharp knife. In my case there were several components that were bad:
These modules are prone to failure due to a design flaw in the circuit, but it can be easily upgraded.
I suggest for everyone who will try to fix their module themselves to change resistor (marked in picture below) from 3.3kohm to 100kohm 0,5 or 1W resistor and also change transistor that drives the warning light from MPS A06 to MPS A14. These changes should prevent CMOS CD4011BE from failing again.
After these changes my low coolant warning light is working again. Light illuminates when ignition is turned on and if coolant lever is sufficient it goes off after few seconds.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
2
Awesome repair report, thanks! One question: It’s my understanding that this coolant level warning system is common on GM cars. Wouldn’t it have been easier to just buy a new unit for a Chevy?
As I am not in US so “Chevy” unit might be even more difficult for me to source then new Jaguar unit Also I’m not 100% sure but I think GM unit uses 2-wire probe.
Anyway it was easier for me just to diagnose and fix the old unit. And the cost of this repair was probably 5$ max.
Hi, Just used a multimeter, nothing fancy. Just to note that when this thing fails, it will not illuminate the red warning light at all. Propperly warking unit should turn on the light on when ignition is on and then turn it off in 5 or so seconds if coolant level is ok.
My car the coolant light flashed intermittently. The light goes on/off when I turn on the key. If I pull the wire off the probe in the coolant tank the light goes on and stays on.
I am going to check the wire from the probe to the sensor.
Hi John
thanks for this guide : I never noticed the light on the dashboard, so decided to take the module from under the dash, open it (I had to use a small saw) and check it’s behaviour
mots components were ok on the test, and even the CMOS reacted as expected,it’s output switching when the “sensor” point is either grounded or left “in air”
but change of its output didn’t change the “signal” output, so I changed the transistor, and took the opportunity to follow your suggestion to increase the 3.3k resistor to 100k
results ! the warning light goes on for 2 seconds when contact is on, then goes off until the sensor is disconnected (with slight delay of about 5 seconds)
I glued the box back using ome black hot glue, then put t back in under the dash
small note for others : my module has a part number DAC7808 instead of RKC5259, but is looking exactly the same as yours from outiside and inside circuits
The CMOS an
Also I’m not 100% sure but I think GM unit uses 2-wire probe.