Good day all,
I am back at my inherited 1976 XJ12. It is running smoothly, although I do have a very high idle. I'll be getting at the AAI soon.
What I am writing about is a sensor on the left-hand cylinder bank in the thermostat housing. I noticed this sensor had its plastic cap knocked off with the harness still plugged into it. I mangled it a bit when removing it as I lost patience trying to find my 28MM wrench. The wrench was still on my Saab's timing tensioner

I've attached detailed pictures of where this sensor is located as well as the sensor itself and all of the markings present. I spent a large amount of time researching this based on the markings and any and all illustrated parts catalogs pertaining to the cooling system for the Series II, of which there aren't many...

Can anyone identify this part, and possibly provide a part number or an IPB to lead me in the right direction?

General vicinity of the left-hand cylinder bank. You can just see the opening in the therm housing forward/left of the dipstick.

More close in photo of the hole in the housing where the sensor was removed from along with it's copper crush gasket.

This is the plugin for the sensor. Leads into the main loom that goes in the manifold gully.

Picture of the housing, top down.

"Inside" face of the sensor and markings.

"Outside" face of the sensor and markings.

Top down sensor markings.

Ruler for scale.

Thanks in advance!

 

not familiar with that engine or age but it sure looks like a coolant temperature sensor, especially if it comes in contact with coolant.

 

That's what I thought as well, however the R/H bank certainly has a coolant sensor. Plus, a coolant temp sensor wouldn't have two wires as most senders/receivers run off of resistance based upon temperature. See attached picture:


I know the R/H is a coolant sensor as there is only a single wire, a resistance-type sender.
Why would the sensor that has broken have two leads on it?

 

On the connector, one wire looks black, which is an earth line, the other looks as if it it's a base colour plus a tracer colour. Can you tell us what those colours are, as it will then narrow down your search for the sensor's purpose. The wire colours use a common UK standard used by Lucas and others.

 

That looks to me like the coolant temp sensor for the injection system ECU.

 

The R/H single wire is a Sender unit for the Gauge, thats all it does.

The L/H is a 2 wire, and the Sensor for the ECU "NORMALLY".in that position.

Fraser is spot on, and the colors will assist with deciphering its use, and may well be something to do with the USA market that we never saw.

All my PreHE V12 had the ECU Sensor in that basic position, with a blanking plug just aft, for something the Aust market never had. They were smaller by a long shot than that one. Smaller hex for sure, about 13 or 14mm from dim memory.

The Bosch Part # for the PreHE ECU Temp Sensor is 0 280 130 025.The thread were smaller than 12mm, maybe 10 (thats pure memory), and the plug and socket were unique, the plug went Inside the Sensor Socket. Very thin White plastic thing.
The Bosh Part # for the HE ECU Sensor is 0 280 130 026. The threads are 12mm with a 19mm Hex, and plug and socket were standard Injector style units.

Then this from D Jetronic books I have.
Temp Sensor Coolant, C42166 is a standard Bosch Sensor. It is 0 280 130 014 (M10 with 2 pin 2.8mm) or 0 280 130 025 with Lucas labeling for ECU Temp Sensing.

 

in my Series 3 XJ-6, the COOLANT TEMP SENSOR has two wires.

Usually a COOLANT TEMP SENDER has one wire only.

 

An ECU temp sensor makes more sense, however, I have a total of 4 sensors in the thermo housings, two for each. Both cylinder banks have a dual post sensor in the front portion, the B bank happens to have two. I'd imagine at least one of these will be a thermo switch for the cooling fans and another would be a cold temp sensor for the cold start injectors.





Looks blue/green to me. Are there any available wiring diagrams or IPB's for the Series II online? I'm really struggling to find those for general usage.

Here is a different forum post with the sensor intact and some notes for the B-bank:
https://forums.jag-lovers.com/t/pre-...sensors/398020
Sensor #2 with a "LS" label on the wiring. I have the labels as well, however they are all well worn off.
That individual also has the cold start switch being the forward sensor on the B bank, and not knowing what the forward sensor is on the A bank. By elimination, it must be an ECU sensor, but for what? The part numbers that have been provided look nothing like what I have.

Curiously, the inside of this bulb sensor is mostly empty other than thin elements. I wonder if this was one wax-filled like the AAI? This reminds me of the "ECU" in early French turbine helicopters, an odd comparison, but a thermo cutoff to disengage the starting system without manual input through electrical currant. VW Type 1 electric chokes work the same way, just with a different result. I suspect this switch works the same way. As the bulb increases in temperature, the posts are internally grounded, turning something off.

 

OK,
Digging around in mt outside library, I found very old PreHE Parts books.

The B Bank water rail:
Forward Housing:
FORWARD most sensor is the Temp Sensor for the ECU, same position as the HE.
Aft of that, nearer the pipe connection, is a "Thermal Valve", and noted as USA, Middle East, Canada, Japan. Thermal valve to what??, no idea, It also "looks" like NO wires, just 2 small spigots.

Other similar valves are noted as "Thermal Vac Valve" and are quite specific, not this one, so I have no idea what is going on in your car.

Rear Housing:
No sensors, swiithes, senders at all.

The A Bank:
Front housing:
Forward most is e Temp Sensor, 2 wires, with a standard looking Injector style socket, NO mention as for what?
Aft of that is the Temp Sender, 1 wire, for the Temp gauge.
Rear Housing:
Forward most is a Temperature Switch, again, no mention as for what.
Aft of that is the heater hose connector.

Now Beer O'Clock, see ya.

 

Thanks for digging into this further. I have found a couple of sensors when searching that have two vacuum ports going into this spot, a 90 degree and straight-up port in the same plug, that falls in line with what your parts book "'looks' like NO wires, just 2 small spigots."
I'm going to dig around with an ohmmeter and see if I can trace the green/blue wire. Black should be ground, but that's an easy one to confirm. I wonder if this damaged sensor has been one of the problems to my 1500 RPM idle? Although I'm near certain that's going to be a stuck AAV, just haven't dug in there yet.

When going back to this other forum post, I have thought about something that I should dig into:
https://forums.jag-lovers.com/t/pre-...nsors/398020/2
The third reply states "On B-bank, I think the item labeled “L.S.” is a vacuum valve which controls the air pump and exhaust gas recirculation system."
I did notice that the exhaust gas recirculation motor on the B bank was flat-out disconnected when I started working on this car, and I know for a fact that the electrical cap on this sensor was broken off before I mangled it in removal.

On another note, could you attach some pictures of that parts book you are referencing, or if there is an ISBN number somewhere in there? I'd like to get my hands on one.

 

The "book" as I call it is notes, and copies from when I was with Jaguar. NO book as such.

I cannot scan anything at the moment, the printer thing has finally died. One day I will look into it, but its been 4 years since I needed to use it, so not important to me.

Your market got a lot of extra sensors etc than we did. Our housings had more blanking plugs in threaded holes than actual sensors/senders, so anything I put is my best guess.

Memory, whats left of that, has me at a thread somewhere years ago about a fan sensor in that position, and it was a PreHE I am sure, but what market, no idea.

That will not be the ECU Temp Sensor, that is further forward, and if that fails, unplugs, has a female moment, that engine is DEAD.

 

After a long while, I finally have an answer to this switch. Part number C44646, Thermal Switch, Exhaust Gas Recirculation. I managed to find a new one out of Australia, so I have ordered it and am waiting on its arrival. The car now drives, albeit with a lot of issues still, and the EGR warning light is illuminated.
What a hassle...In any case, for those reading in the Pre-HE market that has a failed switch aft of the coolant temperature sender, it's an EGR switch