Simon's new Xantia V6 and Leaf blog

[white exec]

Spanish fly, you'd need to be. I'm sure something will get lost in translation, though, but looks speak volumes.

[Mandrake]

Take a copy of the S2 wiring diagram I posted too to show how it should be wired.

[white exec]

Am just printing them both out. Conversation will start with the S2 diagram, which hopefully will be greeted with nods of familiarity. I'm looking forward to it.

[Mandrake]

Just keep in mind that most mechanics don't have much of a detailed grasp of electronics... hence why so many struggle diagnosing today's over complicated ECU ridden cars...

[CitroJim]

hence why so many struggle diagnosing today's over complicated ECU ridden cars...

There was a bit in Practical Classics about this.. The thought is that if an engine ECU fails in an older car then don't try to fix it, just bin it and put a Megasquirt in its place...

That's Ok for the engine but hardly addresses the problem of all the other ECUs. Some have suggested using a suitably programmed Raspberry Pi...

[Skull]

Following this dilemma with disbelief, despite having little electrickery experience and never having owned a S1 Xantia ......

[CitroJim]

Following this dilemma with disbelief.

I find it amazing that it's taken 20 years plus to notice this error...

It might explain why some S1 V6s have run out of coolant and then cooked themselves...

[furriegurrie]

If it makes you feel better they are still messing with this in the C6. This sensor was discontinued, some petrol versions did have the sensor but no plug/wiring connected....

On c6owners there is now a fantastic howto to retrofit a sensor for the C6...

[Stickyfinger]

VW do it with two wires ?

[CitroJim]

If it makes you feel better they are still messing with this in the C6.

I am shocked at that

It just goes to show that as George Santayana said "Those who do not learn history are doomed to repeat it."

[white exec]

VW do it with two wires ?

Not necessarily. It depends what those two probes are connected to. Looks as if the electronics would be external.

[white exec]

OK, back from talking with two Citroen mechanics (at Citroen Velez-Malaga), both electricians.
Both say they are familiar with the 3-wire connection, regard it as normal, and understand how it operates.
Neither could make any sense whatsoever of the S1 2-wire connection to the same sensor, as it lacks any output to anything.
The consensus between them was "trabajo de Viernes tarde" - a Friday afternoon bit of work. They both pointed out that Citroen circuit diagrams contain errors, but were surprised to see the same error on the car itself (I took your photo of the 3-way connector with two-wires with me).

As commented above, it's unbelievable that it's taken 20 years to spot this. Lack of coolant in a PSA engine is a pretty serious matter, as we all know. The implicit mention of Coolant Level monitoring in the Owner's Manual seems a bit naughty, and could lull anyone into assuming it was actually there!

Would be good to get a definitive answer on this.

Anyone managed to drop their level yet?

[Mandrake]

VW do it with two wires ?

Not necessarily. It depends what those two probes are connected to. Looks as if the electronics would be external.

That could be the case, however having an electronics background I should point out that it is actually possible to have a two wire system and have electronics inside the sensor, sharing the same wire for both power and signal, if they're feeling that stingy about the amount of copper cable in use!

You just supply the sensor power via a resistor (or the bulb itself) located at the dashboard end, this provides power for the circuitry in the sensor which may internally regulate down to say 2 volts, when the circuitry detects no water it pulls down the supply wire to 2 volts, which would be enough to light a bulb but still continue to power the sensing circuitry. An even simpler arrangement would be possible with a FET and a single resistor in the sensor.

In fact I was testing for exactly this two wire behaviour on my car to try to figure out if that's how they do it. But even before I saw the circuit diagram Jim posted two things told me that this was not the case -

1) connecting a test bulb to the 12v wire on the plug lit the test bulb (but not the dash bulb!) easily with almost no voltage drop at the pin - thus there is no bulb or resistor in series with the supply. (The circuit later confirmed it comes directly from F2!)

2) The part number for the sensor is the same as that used in the S2 V6 - which clearly uses pin 2 as the signal output. Here on the S1 pin 2 isn't connected, so short of a redesigned sensor it could never work in a 2 pin configuration anyway. The sensor would have to be specifically designed to be able to operate in a 2 pin mode.

Definitely just a **** up in the design. Probably a drafting error which was dutifully followed without question by whoever designed the wiring loom, and not caught by QA or testing until well into production! As the S2 facelift was due in less than a year after the S1 V6 was released they probably decided to defer the fix until the S2 which has a significantly reworked wiring loom throughout the whole car! Sensors still had to be fitted to plug the hole...

Electrically a refit to restore the missing functionality is easy. As we have relatives coming to stay starting next week, then winter I'm not going to go tampering with the car just now but next spring when I have the LHM tank out to do an oil change and filter clean I may see if I can run an extra wire down to the Bitron and get my hands on a 3 pin plug to get it to work. If I do I'll document it on the forum.

[white exec]

Sounds like a plan, Simon.

PS My replacement XM front spheres (don't ask) were finally with me this morning, and will get fitted tomorrow, so a report on the new-type HA valve fitting should be possible quite soon.

[CitroJim]

Chris, sounds like you had an excellent chat with your Citroen mechanics It's good to know they really know their stuff but worrying that the implication is given that other errors exist...

Indeed it is so naughty of Citroen to give every impression the coolant level sensor worked! They must have known. Did they have no test schedule to confirm such things worked correctly on prototypes and selected production cars? Such a cavalier attitude is worthy of British Leyland of the 70s!

Maybe they did know but the production wiring looms had already been made - for a low volume car that was produced for only a few months - and it was ignored and hoped nobody would notice... Seems nobody did for 20 years but they reckoned without you Simon!!!

Alasdair, your two V6 Activas. Are they two or three wires to the sensors? It might be interesting to know now if this issue was confined to looms made for RHD V6s only...

This is turning out to be one of the most interesting threads ever on the FCF...

Chris, good to hear you have your spheres. Looking forward to a ride report update soon!