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I think mine has gone bad, if i ground the wire to the body the light goes off! other than that i cannot make it go out! how does the sensor work? is there another wire somewhere that gives it a ground? I even tried dropping the wire into the coolant thinking that maybe the ground travels through the coolant.
What am i missing??
if the sensor is indeed bad, how does one remove it? doesnt look to be threaded to me!
for some strange reason my phone is not talking to my laptop so i cannot upload picture. maybe sensor os the wrong word, sender perhaps?? its a single spade connector on front side of coolant fill tank! turns on a light on the dash that looks like a radiator! i googled coolant level sensor and it came up! but doesnt tell me how it works!!!
The coolant level sensor/sender in the header tank works in conjunction with the 'low coolant unit' in the dashboard. Together they conspire to operate the warning light.
The low coolant unit is a cylindrical device in the RH component panel behind the glovebox. I really don't know how it works.....never had reason to open one up and see what makes it tick. You can see the illustration and wiring in the S57 Wiring Guide.
The diagram shows that it makes (or perhaps breaks) a ground path...presumably thru the coolant itself? I dunno....but there doesn't seem to be any other way.
Often removing the sensor and giving it a good cleaning will put things right....but make sure you have a new rubber bushing first, part C43221
I also had a fault on the coolant level warning. I changed the probe in the header tank when I was working on the cooling system (ended up with a new aluminium radiator). The warning lamp still did not light up. Then I discovered the bulb was missing! On fitting a new bulb, the warning lamp was on all the time. Now I know why a PO removed the bulb.
The way the circuit works is that the control unit behind the passenger side of the dash is connected to the probe in the header tank. When the probe is immersed in coolant, it completes a circuit to vehicle ground via the engine. So if the wire to the probe is disconnected, the warning lamp should be on (as per the OP in this thread described).
When I checked the control unit wiring, the wire to the probe was fine. Clearly the wire to the warning lamp was fine as the lamp was coming on. 12V was reaching the control unit, but the ground connection was open circuit. I cut the wire form the control unit before the connector plug and made a new ground point behind the dash. However, the warning lamp was still on constantly.
So I removed the control unit and opened it up to see what is inside. It turns out to be a fairly simple circuit, consisting of an oscillator based on a CD4011 quad-input dual NAND logic chip and a transistor which switches the signal to the warning lamp. When the coolant probe is covered by water, the transistor is switched off, so the warning lamp is off. If the coolant drops below the probe level, the resistance to vehicle ground on the probe rises to infinite, and the circuit switches on the transistor at the rate of the oscillator. This means that the warning lamp will flash. Another good aspect of the circuit is that on turning on the vehicle ignition, the warning lamp will illuminate momentarily, thus confirming the bulb is working.
I changed the transistor and the chip on my board,and and now it is working properly. The only other components are 7 resistors, 4 capacitors and a diode (all of which tested good with my multimeter).
My car has the earlier version of the control unit, packaged in a square black box. The later versions in the cylindrical container have a few extra components, designed, I think, to protect the electronics from voltage spikes etc. I think my control unit was perhaps damaged by losing the connection to vehicle ground via the connector. I couldn't trace where this is supposed to be grounded, so the simple solution was to make a new ground behind the dash as described.
Replacing the faulty components cost me just 15 Baht (Thai money) which is equivalent of about 50c US. I used a soldering iron and a solder sucker to de-solder the old components from the board, which was straightforward. I decided to use a MPS A14 transistor instead of the original MPS2222 as the newer type is apparently more robust. Attached a couple of photos of the unit:
Where is the lamp on the dash that signifies low coolant.
The brown plastic header tank that the sensor was plugged in to is not a part f my cooling system.
Aye in my wiring adventures on my installation, I was directed to the cylindrical device as a source of fused volts.. I opted not to chop in to it and find the source elsewhere. Shaped like a cylinder ala film cannister olden days..
Yes an old thread but still relevant and I couldn’t find anyone having reported success with repairing the control unit anywhere else on the forum. Hence added to this so it should appear in a search.
Thank you for your posts, Andy, I was about to start a thread with the same question. Like Carl, I don't have the Jaguar expansion tank but I did form an idea that the "probe" determined whether enough coolant was present or not.
I am using a '92-'97 Camaro radiator which has a built-in port for the appropriate coolant level sensor. I decided to install one with the hopes that the warning light on the dash would go out or come on, as the case may be. The GM sensor has a 2-wire connector and I couldn't find any info on the routing of the circuit. I've wired it with one contact to ground and the other to the WR Jag sensor wire, we'll see if it works when I get everything put back together.
That might well work - if the Camaro level sensor is a float switch, for example, then it will complete the circuit to ground when immersed in water wired as you describe.
To test the module, you can simply remove the WR wire (so it has no connection) and the warning lamp should flash (with ignition on) Ground the WR wire and the warning lamp should be unlit
I don't think it's a float switch, it has a single probe exposed to water and a large area that is probably potted electronics. Where I seem to be having a hard time is the idea that providing a ground (in the water) causes the dash light to go out, just backward of normal thinking. On this GM sensor the probe contacting water would turn off the warning lamp in a GM car as well, but I'm not clear what to do with the second sensor connector contact. The "coolant level unit" in the Jag probably has a counter-part in GM cars to work some kind of magic on the operation of the dash light. I'll just wait until the engine is back together and radiator filled to test. I'm just wondering if BL could have made this minor bit of information any more complicated to pass on to the driver.
Dave
Last edited by LT1 jaguar; Apr 12, 2024 at 07:23 PM.
If the coolant level sensor works like the XJS one, the warning light goes out when the probe is immersed in coolant because the coolant earths (grounds) the circuit. If no coolant then no earth and the light comes on. The electrics (in effect) contain a "normally on" circuit that lights the warning light in the absence of current, and this circuit gets turned off when the system is energised via the probe earthing and making the circuit that turns the light off.
coolant level sensor
