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Discussion Starter #1
I've been having problems with my 2012 2.2 XF overheating in heavy traffic (I've had the message centre warning a few times - I've seen the coolant temperature way over 100C). It returns to 82C when on the move again.

The cooling fan only operates when needed by the air conditioning, but ignores the coolant temperature.

The other day the coolant temperature reached 100C, the engine oil and transmission oil were both 95C - yet the cooling fan still didn't switch on.

One bizarre that may be connected is that the transmission (TCM) shows an incorrect ambient temperature reading of - 11C.
The ambient temperature reading from the sensor on the door mirror was correctly showing 6C.

Any clues?

I'm at a dead end with troubleshooting right now.


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Initial thoughts suggest that the temperature sensor is fubar'd?

Also, Have you checked the fan relay?
 

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Discussion Starter #3
Yeah, the sensor does appear to be a bit dodgy... but I have no idea where it is.

Neither the workshop manual or wiring diagrams give me any information as to where the TCM gets an ambient temperature reading from.

As for the fan relay - I'm not sure I've checked that, but will do tomorrow!

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Discussion Starter #5
Do you have any DTC's on the car ? might not be a sensor wrong reading but a fan power relay failure or the fan itself.
The only DTC's are for the auxiliary coolant pump that circulates coolant into the heater matrix.

I have recieved a replacement auxiliary coolant pump - but I shouldn't imagine this will suddenly make the fan burst into life.

I replaced the fan during the summer - exactly the same behaviour and overheating occurred... the fan again would only operate when demanded by the air conditioning.

I've tested the wiring to the fan for voltage/ground/signal also.

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Discussion Starter #7 (Edited)
There is only one fan - the air con condenser and coolant radiator sit in front of it.

I've just checked the wiring diagram - no relays involved.

I did check all the relevant fuses and connections to the fan months ago - and all was fine.

There is only one set of wiring to the fan... as it works for the air con, a wiring problem seems unlikely?

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100% there is a relay pack ! All cars have a relay pack that control the fan. Must dig in the electronic schema.
Usually the power pack for the fan(s) (when more than 1) is controlled on modern cars by the LIN bus. So your power pack should have some ground , power and a LIN bus wire.
If it works with AC, then maybe ECU does not send signal and that is due to engine temp maybe.
Meassure all collant temp readings you can find in SDD and see if they see the same.
 

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Discussion Starter #9
100% there is a relay pack ! All cars have a relay pack that control the fan. Must dig in the electronic schema.
Ah okay, will check again

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Hmm, wonder if this is a variable speed fan controlled by a PWM module? If so, there could be no relay.
 

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Discussion Starter #11
Hmm, wonder if this is a variable speed fan controlled by a PWM module? If so, there could be no relay.
That seems to be the way.
The fan module (part of the fan) has a permanent 12V connection, ignition connection PWM and ground.

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Then I think the only thing you can do next, short of changing the fan assembly, is to track down the relevant temperature sensor.

Might be worth opening and refastening any connectors in the power and signal lines, just in case a bit of corrosion on a pin or socket is the culprit.
 

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Regardless of the transmission temperature, the fan should be running at full speed if it detects anything is running too hot.

Hasn't there been issues with the pwm module before?
 

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You say you've gotten a new aux cooling pump. Have you checked to make sure the main cooling pump is operational?

The symptoms seem to fit the main pump not circulating the engine coolant..
 

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Discussion Starter #15
You say you've gotten a new aux cooling pump. Have you checked to make sure the main cooling pump is operational?

The symptoms seem to fit the main pump not circulating the engine coolant..
If the main coolant pump wasn't working - wouldn't the car also overheat when on the move?

Also the cabin wouldn't heat up as there'd be no flow to the heater matrix?

The top radiator hose gets hot when the thermostat opens at about 82C - and then the temperature stays within a degree or two of that until I hit heavy traffic.

The bottom radiator hose isn't quite so accessible when the engine is running...



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If the main coolant pump wasn't working - wouldn't the car also overheat when on the move?

Also the cabin wouldn't heat up as there'd be no flow to the heater matrix?

The top radiator hose gets hot when the thermostat opens at about 82C - and then the temperature stays within a degree or two of that until I hit heavy traffic.

The bottom radiator hose isn't quite so accessible when the engine is running...



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Good point.


What if you have a main coolant pump that is on its way out, so you're getting circulation - but just ineffectively?

Your symptoms may also point to a blockage or partial blockage.
 

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Still does not explain why, if the coolant is over-temperature, the fan doesn't come on.
 

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Still does not explain why, if the coolant is over-temperature, the fan doesn't come on.
Probably right Wilf.

I haven't got the manuals to hand. Is there a thermostat valve in the 2.2 coolant circuit?
 

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Discussion Starter #19
Probably right Wilf.

I haven't got the manuals to hand. Is there a thermostat valve in the 2.2 coolant circuit?
It's bolted to the back of the engine next to the bulkhead - access to it is limited to say the least.

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When I bought my car (2010 5.0 NA) it had similar, but not identical, problems with overheating. Or rather erronous overheating indication. After driving for 20 minutes or so, the orange overheating warning was shown, followed a minute later or so by red. The car acted like it had overheated, immediately on red warning the air condition was turned off (which once caused me to nearly crash on the motorway when the windscreen fogged up in three seconds or so :eek: ) , and cooling fans ran on high speed until several minutes after stopping the engine. However, I could not see any evidence of actual overheating.

A lot of things were attempted by both the dealer where I bought the car and the licensed Jaguar workshop, including new thermostat, new engine coolant temperature sensor, troubleshooting a lot of wiring and I don't know what else. What cured it was when they replaced a temperature sensor - I don't know what this sensor measured - that required taking out the gear box to be able to access this sensor (!).
 
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