New to me 2005 3.0L with 102xxx miles.
At high ambient (>105 or so) the AC works for a while then drops out and attempts to cycle every few seconds. Cooling fans will not come on and the car overheats. If I turn the ignition off and let the car sit for 4 - 5 minutes the fans come on and if I restart all is well. At lower ambients say mid 80s things work as expected. Even at high ambients if I don't turn on the AC the fans cycle as expected and temp stays mormal (180 - 190) measured with IR thermometer at the coolant sensor. Recently replaced the coolant sensor. If I substitute a 100 ohm resistor for the coolant sensor while the fans are not working they do not activate. Any help much appreciated. For the record I am located in Tucson AZ where temps in excess of 100 often approaching 120 are the norm in the summer months.

 

So the easiest shade tree mechanic trick on our kitties to make sure the fans are "working correctly" is turn a/c to as cold as possible (not automatic). This "overrides" the variable fan speeds. Raise hood and lean in over radiator and or shine a light on both fans. You should get a face full of moving air and both fans should be turning at top speed.
If this does not occur, your FCM (fan control module) is the problem. Replace it ONLY with a Gates 134 module not a cheap Asian one (many, many forum horror stories for years about these).

 

Pardon my scepticism but why would the fan control module which is the only thing that drives the fans work under many conditions and not under others? At one point I thought that perhaps the FCM was heat sensitive and I checked the temp of the module with fans working and not. The temp was lower with fans not working than it was with fans working by 10-15 degrees. Your approach assumes the fcm is getting power and a proper signal from the ecm. With the AC cycling and not running as it should I'm not sure I want to make that assumption. Does anyone have a relatively easy way to test the input to the fan module? Replacing the fcm is a fairly expensive option and I would like a bit more evidence.
I strongly suspect something else is at play.

 

Read all the links as well

https://www.jaguarforums.com/forum/x...issues-211959/

 

I have read all that more than once. I don't think it covers my problem.

 

OK, I prefer the V12's, much simpler and easier to live with.

My 2010 had the fans come on and stay on until the battery was disconnected.

Did the basics, as mentioned, nothing found that made sense.

Old employer, yes, I am that old, GAVE me an Asian module to use while I did the suck and see. Fans ON whenever the key was ON, but stopped whenever the A/C was activated, bugga, but being winter,m who cares.

He then had a 2008 come in that was a write off, and the front was OK, so he lent me the OE module from that car. This returned mine to OE status, and everything did as designed.

Ordered an FCM134 Gates from Rock Auto, and 7 days later fitted it, and returned the loaner. Car is as made, and I have moved on.

WHY, who knows, I dont.
Care factor, below zero.
Its a "pretend Jag" to me, and does what I want, and will do for the next 5 years the law will allow me to drive in this country.

If that offends some, so be it.

Delll's huge thtread, and Thermo's equal thread, helped me understand some of the nonsense, add to that the fact the OE loner sorted the beast, made sense. Electrickery in ANY engine bay is on borrowed time, FACT.

When Spring kicks in here, I will bring out the MK X and put "Pretend" away, and move that module out of the engine bay, ready for Summer, which should help it and me for a while.

 

Because it's a "Kitty" and you must expect furballs from time to time. 🤣🤣🤣

 

Thanks for the support folks. I tend to struggle with things that don't make sense most likely because lack of understanding complex systems.
Sometimes one longs for the days gone by when vehicles were at most electromechanical and a little easier to deal with. I am working to have a local fellow who is a retired factroy trained Jaguar mechanic take a look. He apparrently has the proper diagnostic tools which should help pinpoint the problem.
Time will tell.

 

Be sure to let us know the outcome. It may help another member in the future.

 

Well my Jaguar guru was not much help. He suggests that he doesn't work on cars with rebuilt titles and furthermore it will probably cost more to fix than it is worth. He asked if I was willing to pay $1000 for an alternator plus diagnostic and labor in addition to $700 ditto for a fan module. The alternator is because the alternator light is intermittent. He is correct that I would like to get out with much less expense. I can live with the alternator if i can get the overheating solved.
I just replaced the water pump and the leak and noise seems to be gone. I doubt that will have any effect on my other problems. I had one bolt that was stuck and I had to finess out but once that was done it was a snap.

 

It would really be nice to find a way to get a meter or scope hooked up at the various connectors but I can't see any way to do that without some sort of break out box. Anybody have a solution? Any body ever try a clip on meter? Probably not very accurate but perhaps better than nothing?

 

FWIW - I think debugging a complex module with a meter is a long shot. You might be able to detect an open circuit where there shouldn't be one, then maybe fix a dry solder joint. A meter can definitely be used to test the inputs to a module to make sure its getting power at the right time and the right volts and discretes for logic. Some modules are fed by pulses and waveforms, so the meter will only get you so far. Good luck with the repairs!

-Dave

 

As I understand it there are meters that will measure PWM signals as a percentage and I also have an ocilloscope.

 

You never posted if you did the "coldest possible a/c" test to see if fans were/are running full speed. Do them with a cold car (not driven) if fans full force FCM probably (?) Ok.

As for alternators failing as Thermo has stated many times, they're pretty bullet proof. Not that there's not failure, just very RARE that they do fail.

 

I'm like you, because I do not understand the fan controller I refuse to accept it's magic. Talk about an overly complicated or misunderstood piece of equipment...
I am waiting on a new fan unit as I think mine are drawing too much current combined. Measure your start up current on each fan direct to battery and see what you get. You can use a handful of cheap fuses and jumpers if you don't have a meter. You can read this if you haven't already...
https://www.jaguarforums.com/forum/x...thread-281668/

 

After changing the water pump, it's early days and today is not very hot at 98 but all seems to work as it should. The fans come on low shotrly switch to high. Drive around a bit let things warm up then park and idle. AC remains on with fans high. The temp at the coolant sensor is reading 174.x and holding. Prior to changing the water pump it was 180.x to 190.x.
Let it sit for a 10 minutes, restarted and all is well. Idled for 5 munutes and everything stable.

Waiting for the next hot day to see if it holds.

 

The fan control module simply receives the PWM drive signal from the ECM and uses that to ascertain what fans to turn on and to what degree.
Internally the FCM processes the PWM input ratio and has an internal pre-programmed threshold at which point it will move from driving one fan to then calling the second fan to join into sharing the workload.

You can pick up cheap PWM generators online that allow you to set the frequency and also the PWM ratio.
Their output voltage is proportional to the input voltage, so if you are feeding it with 5V then you get a 0-5 volt PWM , conversely if you have a 12 volt supply it will output 0-12v PWM waveform.
From the electrical schematic the FCM is controlled by a 140Hz PWM signal that ranges between 7% and 95% positive duty cycle.
I don't know if it is driven with a 5 or 12 volt signal level though, but you could scope yours to see what the ECM is outputting before you try to bench test with an external PWM generator.

 

Mark that is good info to have. How can I connect a meter or scope to the pwm input line to see what signal the fan control module is getting? It seems pretty simple if you can measure the inputs to the fcm to see if the fans should be running and if not then the fcm is at fault.

 

Hotter today - still have the problem.
Swapped R5 and R7, ignition relay and Inerta switch, according to my Haynes manual. I don't see what R7 has to do with inertia.

R7 feeds power to the fan control module and has aparrently become intermittent. R5 is listed as the ignition relay seems to have less asked of it so it worked with the intermittent relay. Not trusting that relay I rplaced it putting the new relay in R7 which seems to have the higher current as it is in line with an 80 amp fuse.
Prior to changing the relays the Fans and AC would cut out after 5-7 minutes at high ambient. After changing relays I let it idle for about 30 minutes took it for a drive and all remains well. Again early days but I believe I have found the guilty party. I suspose I could put the bad realy back in and confirm that the problem returns but I think I will leave sleeping dogs lie. I will update if the problem returns. Thanks to everyone who replied and I hope this might help some other poor soul with similar problems.

 

The PWM signal is on the White wire with the blue stripe.
You can intercept that White/Blue wire at three possible locations:-

• FCM (JB190 4 way black connector adjacent to radiator, pin 4) ,
• JB145, 8 way black connector pin 7 (part of the engine harness LH side of engine compartment)
• Or the ECM connector (the 134 way connector EN16 pin 51).

So I probably don't need to say this but you also need to pick up a ground for your scope probe, found on:-
JB190 pin 2 (Black wire)
I don't think JB145 has an earth wire (so use a nearby grounding point stud)
EN16 ECM plug has numerous grounds as black wires but there a re some black wires that are not grounds, so just use a grounding point stud.

As far as getting a probe connection....... you can slip a fine pin up through the small seal around each wire to be able to touch the metal connector inside the plug. That spares you trying to break into the wire sheathing.
You can get some little insulated testing probes that are for this purpose, but if your partner has some sewing pins laying around, you can just disappear a couple into your workshop that will do the job.