I am trying to make my 1994 XJ6 roadworthy after a long term downtime and I thought I was making progress but I just recently discovered that I have two issues that I am now wondering if they are related.
Neither of the two engine cooling fans seem to be coming on even when the temperature of the engine gets VERY hot.
Also the climate controls on the center console seem to be totally dead as well. All of the buttons between the two dials that allow selection of AC or recirculated air do nothing. The only thing that does anything at all is when I use the fan speed control switch and move it to defrost I can hear a relay down in the passenger's footwell clicking as the speed control is rotated from High to Defrost.

Is it possible that these two problems might be related? I know one of the engine fans is supposed to be activated by the selection of AC in the climate control so I thought perhaps there might be a common problem here.

Any and all suggestions would be most welcome.
--
Steve

 

Have you reflowed the solder connections in the fuse boxes? The footwell fuse boxes cause lots of problems as the boards tend corrode or flex causing the joints crack.

Lots of threads on how-to's if you haven't done it (YET)

The 94's like ours have more fusebox issues than the earlier cars, could be the soldering robot on the production line was hiccuping.

Anyway, just a suggestion.

Larry

 

No, I have not done this. How difficult is it to get one of those footwell fuse boxes out of the car to do this?

 

Not too bad, unplug all the stuff at the back and then just a couple of screws.

Larry

 

But what is the process to get to the back of the fuse box in order to access all of the wires?
I know I also have a FUSE 1 failure showing on the VCM display for the car and when I investigated this I an not able to find any blown fuses.
Could this be an indication of a failed circuit or board?

 

The procedure is sit in or around the door footplate or in the footwell, remove the plastic trim by turning the screw a quarter of a turn, then reach around the back of the fuse box to the harnesses, unplug each large plug one at a time. There are three or four I think, can't remember- it was quite a few years ago I did the job.

The plugs only fit their own sockets so you can't mix them up. You have to squeeze the locking tab on the plug to allow the plug to br removed.

Don't know ..Can't be good though if you can't find a blown fuse ...are you sure all the fuses are OK?

Fuse 1 (I think) is the passenger side footwell fuse box. I can't say for sure you have an issue with the fuse box joints, but it is a common problem as these old crates enter their dotage.

Larry

 

Hi Steve,

If I understand your issues, the engine cooling fans are inoperative, but also the passenger cabin climate control blower fans are inoperative along with most of the climate control panel controls?

You can download the wiring diagrams at this link:

Jaguar XJ40 Electrical Guide 1993-1994

The engine cooling fan circuit is convoluted and I can never remember the detals about when they are wired in parallel or series, but you can see the schematic on pdf page 79 of the Electrical Guide. Just a quick glance at the schematic suggests fan inopertation could be caused by a problem with one of the two refrigerant pressure switches, the radiator thermal switch, or the fan ground. Since the radiator thermal switch won't close the low-temp contacts until the coolant reaches 186F, a stuck-open coolant thermostat might not allow the coolant to reach the activation temperature. You could test by shorting the White wire in the switch connector to ground to see if at least one fan ru

All of the XJ40 relay modules suffer from the same kinds of cold/starved/cracked solder joints as the fuse boxes Larry mentioned, so it might be worth opening up the Fan Control Relay Module to inspect the condition of the solder joints, especially around large relay mounting pins. The module is a small plastic box (black in color, I think), mounted either just to the left of the radiator behind the left headlamp or on the left inner wheel well.

The FUSE 1 warning, if I recall correctly, may have something to do with an inline fuse mounted in the harness behind the right knee bolster or glovebox/airbag. I can't recall the details, but it's possible that fuse has something to do with your climate control problem.

The Climate Control system is complex, but it sounds like at least part of your problem is power supply to the control panel, which comes from the Climate Control Microprocessor (CCM), which is mounted on the right side of the Climate Control Unit behind the right footwell carpet. It would be worth checking the integrity of the electrical connections at the microprocessor and the climate control panel itself. Power for the CCM comes via the Auxiliary Power Relay, which is in Relay Module H1 mounted behind the right knee bolster/underpanel. This is another one of the modules that can suffer from poor solder joints, so it's worth taking it apart and inspecting and reflowing/supplementing the solder joints. Before you do that though, check some of the other circuits powered by the Auxiliary Power Relay - if they are working, the relay is probably working. You can trace the other circuits beginning on pdf page 19 of the Electrical Guide.

I don't see that the ECM is involved in the radiator fan operation, so a problem with the Coolant Temperature Sensor (CTS) probably could not prevent the fans from running.

My brain is tired so I'll leave it at that for now but will try to think of other things you can check.

Cheers,

Don

 

Thanks for all of the suggestions Lawrence and Don
Where is the ground for the fan circuit actually located?
I am heading over to my shop now to test the fan switch and I would like to at least check the integrity of the ground.

 

I think it's one of the grounds on the left hand side of the engine bay - maybe the one on the left inner wheel well. In the Electrical Guide, the page before each wiring schematic lists the components and their general locations.

Also, I forgot to mention that it is possible for the radiator fan motors to fail. Not simultaneously, usually, but if one failed and the owner didn't notice and continued to drive the car, the other fan could subsequently fail. The fans and motors are the same on X300s and X308s, just the electrical connectors changed. I installed good salvaged X308 fans in our '93.

Cheers,

Don

 

I pulled the connector off the fan switch on the bottom of the radiator and found a bunch of corrosion inside the terminals of the switch and the connector that snaps onto the switch.
However even though I know this is not good, I do not believe this is the real root cause of the problem.
When I looked at the wiring diagram that Don was kind enough to provide, I see that there should be power flowing to this thermostatic switch from the fan control relay so when the car reaches a critical temperature that activates the switch the switch will trip and allow a circuit to ground through the black wire on the switch. When I checked these white wire connections on the connector, there is no power in either terminal.
So I then looked at the fan control relay and pulled the wiring plug off of that relay. I have power to the relay through the big brown wire and from the big black with white wire.
I also checked fuse A2 and A7 in the left hand fuse box and these are good and have power to both legs of the fuse.
I believe my problem is with the fan control relay. I looked at the relay and it seems pretty well sealed up so I do not see a way to take the cover off the relay to get to the internal contacts.

Anyone here have experience with fixing or cleaning up a non-working fan control relay?


All the wires going to the fan control relay. See the big brown wire and the big black with white wires that connect to terminals 3 and 5.



Maybe defective fan control relay

No corrosion inside relay connector

No corrosion inside relay terminals


Corroded fan switch connector

Corroded terminals on the fan switch

 

Not suggesting you are on the wrong track, sounds good an' all, but just a small FYI ..

With a defective fusebox, it will still show "good" on both sides of the fuse ...the problem is what happens afterwards - when the flow heads off to the harness THROUGH the fusebox solder joints at the rear.

Larry

 

Hi Steve,

I just took a look at the schematic, and the coils in the two relays inside the fan relay module are connected to ground when the thermal switch closes, so without a good connection through the switch, you will have no power from the relay. As a test, you could try installing the relay in its socket and backprobing a wire into the relay socket connector to the wire that connects to terminal 9 of the relay socket. Connect the other end of your backprobed wire to a good ground, then see if your fans will run (turn the A/C on to see if you can force them to run). If the fans do run, the problem is the corrosion on the thermal switch connector terminals, the switch itself, or both.

Cheers,

Don

 

Thanks for the excellent suggestions Lawrence and Don.
Don, the problem is if you recall my climate control is also dead so I cannot turn on the AC.
If I am reading the electrical schematic correctly, the corrosion of the terminal on the thermostatic switch wiring connector and actual terminal in the thermostatic switch which is the center terminal of the three is LS58-2. This is in fact the wire that leads to terminal LS68-9 on the relay.

 

According to the schematic, the wire that connects those two pins is white, and it is this wire that is connected to ground when the radiator fan relay closes when the coolant temp reaches 186F.

I had forgotten about your climate control panel, but not to worry. Looking at the schematic again, the white wire connected to LS68-9 on the relay base is grounded when the coolant temp reaches 186F or the A/C, and the fans should be forced to run when the refrigerant pressure switch (single) is closed, which connects the Yellow/White wire to ground. And the fans should run on high speed when the White/Blue wire at the refrigerant pressure switch (triple) is also connected to ground. So you should be able to rig up a test by using paper clips or small alligator clip test leads to jump all these connections and bypass the pressure switches.

Cheers,

Don

 

I went out and pulled the LS26 connector apart and I only have power on the LS26-1 terminal which is the solid purple wire.
This circuit diagram for the inside of the fan control relay is very complex and I'm afraid too much for me to grasp.
So I am not sure if having power to only the LS26-1 terminal is a normal thing or not.
I am trying to figure out if there is some way I can make a ground somewhere to definitely test one or both of the circuits.
I know that earlier this summer when I was reinstalling the cylinder head after changing the head gasket, I tested the fans that were on the car and determined that one of my other spare fan assemblies worked much better so I installed that fan assembly.
I could try pulling it off again so I could retest it but I am fairly certain that the problem is not the actual fan motors.

 

OK, perhaps I am dense here but it is unclear to me if multiple connections have to be grounded to test one or both of the fan circuits.

Does the white wire from LS68-9 AND another terminal in one or more of the pressure switches have to be grounded at the same time to get the fans to turn on?

 

You're not dense! The setup of the relays and fan motors is definitely complex. Years ago I studied it until I figured it out, but I've forgotten the details - I should have kept my notes. If I recall, under certain circumstances one fan runs. Under other circumstances both fans run in series, and under others, both fans run in parallel. All those relay contacts and diodes in the module are responsible for routing the current accordingly.

My suggestion was to try shorting the A/C pressure switch harnesses with paperclips bent into a U shape, then short the white wire to ground to see if the fans will run. That is based on an assumption that two or more of those conditions may have to be satisfied for the fans to run. But I may be wrong. I haven't had time to re-study all the connections again. The way I figured it out before was to print three or four copies of that schematic, then use a highlighter to trace which wires the current followed when certain relay contacts were closed. You then have a good visual to understand what is supposed to happen and what triggers are required to run each or both fans. Sorry my time is limited and I can't do it now, but I hope that helps you figure it out.

Cheers,

Don

 

Thanks for your continued interest Don
Bryan from the XJ40 list on the Jag-Lovers forum has made me aware of a power flow problem with my car. I had reported here and on that forum that the fan control relay socket only has power to pins 3 and 5 (checked with the relay unplugged).
He tells me that pin 6 should also have constant power. The strange thing is that the power flowing to pin 6 of the relay socket also goes to pin 1 of the LS26 wiring plug that leads to the right fan motor. With the LS26 wiring plug unplugged I definitely have power at pin 1 of the female part of the plug so in theory I should ALSO have power at pin 6 of the relay socket since according to the wiring diagram shown on figure 29 of the 93 - 94 electrical guide these two points are fed by a common harness.

After reading Bryan's posts this morning, I went out and rechecked this and confirmed my earlier findings. Power at pin 1 of LS26 but no power at pin 6 of the relay socket.

If I did not have power at either point then I would be looking at the back of the fuse box for a power flow issue from fuse A2 in the left fuse panel as suggested by Lawrence.

Since I definitely do not have power at pin 6 of the relay socket and have power at pin 1 of the LS26 connector, there MUST be some problem with the wiring harness between pin 1 of LS26 and pin 6 of the relay socket.
I really don't want to be cutting into the factory harness but it seems like I might have to do that.

Any opinions on all of this?

 

Pulling the fusebox and doing a quick re-flow is no big deal, maybe an hour or two, then you can eliminate that possibility, no cutting involved.

If you unplug the harness containing the wire in question and have continuity to the relay or whatever, then the fault IS with the fusebox.

Larry

 

Right now I am looking at removing the plastic cover around the left fuse box so I can look at the wires on the back of fuse A2.
I traced the two purple wires from pin 6 on the relay socket and pin 1 on the LS26 wiring plug and they both disappear up into the wiring harness that seems to lead towards the left hand fuse box.
However it seems that the dead pedal down in the footwell has to come off in order to pull the plastic cover without breaking it.
Looking at the dead pedal now to see how it is attached to the car.