Intermittent 'STOP' & red temp gauge flashing

[AdieuHydropneumatic]

Hello Board, 1st time poster here.
2002 Citroen Xsara LX 2.0HDi 90BHP.
Bought car from next door neighbour in Nov 17. 98,000, full service history, a bit of a ‘Peach’ in trade vernacular. They said that the coolant gauge red light and centre STOP light would occasionally flash for a few moments but the last 2 services had not been able to trace problem.
15 months, 12,000, A/C & full service later, still doing the same for maybe no more than 30 seconds with following observations: When red lights flash, temp gauge at zero & a fan runs. When the red lights go out, temp gauge jumps to mid way-90C then drops back a bit & no fan noise (only noticed this when I’ve occasionally pulled over to see/hear what car is doing). No different during last summers swelterer when A/C was on quite a bit!
Thanks in advance for any help
Cheers

[wheeler]

My first thoughts here is a faulty coolant temperature sensor?? I would have thought somone would already have tried that if its been ongoing for so long?? Is it a single or twin cooling fan setup? On models with twin fan this can also happen when there is a fault with one of the fans.

[AdieuHydropneumatic]

Hi wheeler and thanks for reply.
From what I can see it is only one very large fan behind radiator. If there is another one I can't see it.

[white exec]

There seems to be only one coolant temp sensor on the Xsara 2.0 HDi's...

Click to enlarge

This one sensor obvious feeds temp into for
- gauge
- fuel injection
- over-temp warning (STOP etc)
...previously done on earlier engines by three separate sensors on the water outlet.

So if misbehaving (sensor out-of-spec, poor contact?) this would affect a good deal of the system.
Might be worth replacing it anyway? Pt.no. 1338.C1.
Others know this engine better than I do, though.

[AdieuHydropneumatic]

Hi Chris & thanks for reply.
I can just about see the green sensor as described but it's under thick pipes & wiring. Does anyone know of any pics or videos and 'do's & dont's that may help me get to it without messing up anything else?
Thanks guys & girls

[GiveMeABreak]

Pop your VIN up for me and I'll see what I have.

[sparksie]

We had to change the temperature sensor on a Xara (not Picasso) a long time ago.
I don't think it was a diesel, though.
What sticks in my mind about it is the housing was plastic and the brass threaded bush came out with the sensor. Thankfully, it wasn't me!
Looking at the diagram supplied by Chris, I don't think this is likely here, but the position of the sensor, hidden under a pile of other stuff, is fairly typical. As Haynes were fond of saying, this is a task that usually requires a degree of manual dexterity.

[AdieuHydropneumatic]

Hi Mark & thanks in advance
VIN: VF7**************[VIN obfuscated, can be read by forum staff]
Cheers!

[GiveMeABreak]

Right, on your Xsara you have 3 fan speeds. The engine ECU controls the Slow and Fast Speeds and the BSI controls the medium speed. This is the info I have on the Cooling circuit.

Calculating the fan unit speed
The engine ECU sets the fan unit speed instruction depending on the following parameters:

• Engine coolant temperature measured by the sensor
• Cooling requirement linked to air conditioning, controlled by the B.R.A.C

Checking the fan unit speed
The fan unit is fitted with 3 functioning speeds:

• The engine ECU controls the slow speed and the fast speed
• The BSI controls the mid speed, depending on the information delivered by the engine ECU via the CAN network (engine coolant and air con circuit pressure temperature)

Key:
+APC: + ignition on
+ BAT: Battery +

BSI	Built-in systems interface
1320	Engine ECU
1304	Injection double relay (built-in systems interface)
1508	Slow speed control relay
1509	Fast speed control relay
1510	electric cooling fan unit
1514	Medium speed control relay

• Slow speed is obtained by supplying the cooling fan via a resistor arranged in series in the supply circuit.
• Medium speed is obtained by supplying the cooling fan via two parallel resistors on the supply circuit.
• Fast speed is obtained by supplying the cooling fan directly.
• The 2 resistors are located on the front dash, near the air-air exchanger and the fan unit.

Post ventilation
When stopping the engine, the engine ECU controls the post cooling (slow speed), if the measured engine coolant temperature is over a programmed level.

The fan unit cannot be started in the following cases:

• Operation in power latch (*)
• Switching off of the engine ECU electronics
• Engine starting phase

(*): Mode in which the equipment remains supplied for a period after the ignition is switched off.

Back-up mode
A fault concerning the fan unit (or the slow and fast speed controls) leads it to work in fast speed.

Control in relation to the engine coolant temperature

Principles
The control in relation to the engine coolant temperature is in steps . Three temperature intervals allow the fan unit to operate either in slow speed, or in mid speed, or in fast speed. The engine coolant temperature sensor, installed on the coolant outlet housing, informs the engine ECU of the temperature of the engine coolant.

Flow Chart

Key:
Single arrow: Wire connection
Triple arrow: Multiplexed connection

BSI	Built-in systems interface
0004	Instrument panel
1220	engine coolant temperature sensor
1320	Engine ECU
1510	electric cooling fan unit
0049	multifunction screen

No. of link	Signal	Nature of signal
1	Engine coolant temperature information	Analogue
2	Engine coolant temperature information. Information on the engine coolant temperature alert	CAN
3	Displaying of a warning message	Comfort VAN
4	Engine coolant temperature information. Information on the engine coolant temperature alert	Comfort VAN
5	Fan unit mid speed control	All or nothing
6	Control of cooling fan in slow speed	All or nothing
7	Control of cooling fan in fast speed	All or nothing
8	Cooling fan rotation information (diagnosis)	All or nothing

• If the temperature is between 94 °C and 97 °C the engine ECU controls the fan unit to operate slow speed
• If the temperature is between 98 °C and 110 °C the engine ECU commands the cooling fan to operate at medium speed
• If the temperature is between 102 °C and 105 °C the engine ECU controls the fan unit to operate fast speed

Engine water temperature warning

Action	Appearance of the engine coolant temperature warning
"IF" condition	The measured temperature is over the programmed level (118°C)
"OR" condition	Engine coolant temperature sensor fault
Display	Display of the warning lamp STOP and of the engine coolant temperature warning lamp on the instrument panel (*) A message is displayed on the multifunction screen (*)

(*): (according to model).

Back-up mode
An engine coolant temperature sensor fault leads to the following actions:

• Operation of the cooling fan at fast speed
• Switching off of the air conditioning compressor
• Display of the warning lamp STOP and of the engine coolant temperature warning lamp on the instrument panel (according to model)
• A message is displayed on the multifunction screen
• To record a fault in the engine ECU

Incidence of the air conditioning

Service
For the cooling of the condensor, the B.R.A.C function (cooling requirement of the air conditioning) integrated in the engine ECU supplies to the F.R.I.C function a speed requirement according to the pressure of the air con circuit.
The linear pressure sensor, located on the condenser, supplies a voltage proportionally to the air con circuit pressure.

Flow Chart

Key:
Single arrow: Wire connection
Triple arrow: Multiplexed connection

BSI	Built-in systems interface
8007	Linear pressure sensor
1320	Engine ECU
1510	electric cooling fan unit

Connections

No. of link	signal	Nature of signal
5	Fan unit mid speed control	All or nothing
6	Control of cooling fan in slow speed	All or nothing
7	Control of cooling fan in fast speed	All or nothing
8	Cooling fan rotation information (diagnosis)	All or nothing
9	Air conditioning circuit pressure	Analogue
10	Air conditioning circuit pressure	CAN

Description

Stage	Details
A	Receiving the signal of the linear pressure sensor by wire connection from the engine ECU Transmitting the refrigeration circuit pressure to the built-in systems interface from the engine ECU on CAN network
B	PRESSURE > 10 bars. The engine ECU controls the slow speed of the fan unit PRESSURE > 17 bars. The built-in systems interface controls the mid speed of the fan unit PRESSURE > 22 bars. The engine ECU controls the fast speed of the fan unit

Key:

• " a": Cooling fan unit speeds triggering thresholds
• "b": Fan unit speeds untriggering limits
• A: Slow speed
• B: Average speed
• C: High speed
• P: Pressure (in bars)

Back Up Mode

A failure of the air conditioning circuit pressure sensor results in the following actions:

• Preventing the cooling compressor starting (controlled by the built-in systems interface on request of the air conditioning)
• To record a fault in the engine ECU

The cooling fan is no longer operational for the purpose of cooling associated with the air conditioning.

Here's the Outlet Tank and the water temperature sensor is number 9 on the diagram. The thermostat is number 7.
The coolant Sensor is part number: 1338C1 and costs £43.14 brand new from Citroen. inc. VAT


Click Diagram to Zoom

Here is the diagram showing the Fan and the relays mentioned above:

[AdieuHydropneumatic]

Many thanks to those who responded to my problem.
New sensor fitted and (so far..fingers crossed) all seems good
Thanks again
Cheers