Intermittent Fault

[devans4004@aol.com]

Hi,
I have an intermittent fault on my XJ8, 1999, that my local Jaguar garage has not been able to fix.
Basically, once the car is fully warmed up, if you turn the ignition off and leave the car for about 10 minutes, when you turn the ignition back on a series of faults come up and the car refuses to start. However, leave the car until the engine has cooled down and it starts and behaves as though nothing was wrong.
However, I noticed that when you turn the ignition on, whilst the fault is there, the needle on the temperature gauge goes up the scale about a third of the way and then comes straight back down - this is whilst the engine is still quite hot. Now, reset the ECU and, although the other faults are still there, the temperature gauge needle does not move from zero.
Can anyone please tell me all the parts involved in relaying the engine temperature to the temperature gauge? Yes, I have renewed the coolant temperature sensor.
Because the fault is intermittent, I am thinking of renewing all the items that would leave the temperature gauge registering zero whilst the engine is still quite warm and once the ECU has been reset - desperate measures ehh!
Here's hoping.
Dave

[J44EAG]

There is I believe a fuel temperature sensor on probably the O/S fuel rail to the injectors as I recall. You might investigate that component, wiring and plug. You could with luck just have a poor connection.

I had a few similar issues with my 350R at one time. Essentially the core arrangement is nearly the same as on a 308. I soon learned that the ECU looks every 30 seconds at the various sensors to ensure the perameters are within limits. If one of them is missing an out put or has gone duff, then you can get this type of problem.

Ideally, you need to scan the car with a diagnostic tool. That often gives some idea of where to start looking and with luck may give a fault code. The iCarsoft 930i at around £90 is a very good unit, Foxwell also produce a unit, but the ebay sourced ELM327 bluetooth chip and an Android or Iphone used with a reasonably priced Torque Pro app is also worth buying. All units will probably point you in the right direction. They make diagnostics so much easier and make a very necessary addition to a DIY maintainers tool kit.

Sit tight. Others will see this thread shortly and may be able to offer more advice.

Mike K

[devans4004@aol.com]

Hi Mike,
Thank you very much for taking the time to reply.
I'll look up details about the fuel temperature sensor and it's connections.
I actually have a Foxwell scanner but, unfortunately, when the fault is on the car, even Jaguars diagnostics equipment does not indicate the problem and no evidence is left after the fault clears itself - frustrating or what!!
The only component that did register as a problem was the coolant temperature sensor and that has been renewed.
For anyone else reading this, the four faults that scroll on the MIL are: Trac Not Available, Asc Not Available, Gearbox Fault and Engine in Failsafe mode. Once the engine has cooled down sufficiently, all faults disappear and it is like there was never a problem.
There cannot be that many components that are common to all these faults and the peculiar performance of the temperature gauge.
Many thanks once again.
Regards
Dave

[RichardSEL]

I've been watching the "TRAC NOT AVAILABLE" flashing up on MFD of my 3.2L XJ8 ('01MY)
It appears when I turn over the starter motor -- ie when battery volts are temporarily lowered
at maximum current take of the starter motor
That seems to come up after an overnight stand, but not soon after a long run -- lower vs higher terminal volts
Battery is a seven months' old Bosch

I've just been on the JEC jolly to Coventry / Vulcan bomber and back, M1 going up, M40 return and
it didn't flash up yesterday on startup about 17 hours after my return home. So fully charged.

But doing a most every other day commute of about 22 miles it does flash up.
This indicates to me that there's something more fundamental to our wiring as a poor connection -- as you're getting "TRAC NOT AVAILABLE" flashing up too. Thus a volts drop at starter motor time when the current demanded is max.

It may be that's what setting off your sensors' faults and unless coolness returns the ECU isn't seeing a correct
input that it requires and so does it's "there's something wrong" routine and doesn't allow IGN (?)

For mine, I'm only guessing at this stage. I'll have to clear out the boot then re-do by way of solder joints all
the connections from the battery terminals I can reach. Those crimped-on wire connections can just corrode over time
at their crimp areas. There's also a negative that goes to the bodywork from the battery negative terminal I believe.
That'd need the solder-in treatment to the crimps. And cleaning of the bodywork and spade terminal to bare metal at the other.

These crimped cables are a common source of curse. Especially on modern days cars. Neighbour's Ducato would only
turn over very slowly on starter motor. But by co-incidence he made his battery negative to engine with jump lead
and whey! started perfectly every time. Changed the lead (bought the correct one from Fiat -- so repeating the fault
for the future ) And it's been perfect since

Throwing this into the thread as an item to eliminate -- it may not be your fault -- but at least you'd know for sure your fundementals at battery were correct. How old's your battery BTW?

[devans4004@aol.com]

Hi RichardSEL,

Thanks for taking the time to respond. My 'Trac Not Available', 'Asc Not Available', 'Gearbox Fault', and 'Engine in Failsafe mode' errors all come up before I even attempt to turn the engine over. This along with the quirky Temperature gauge behaviour.
Assuming it was something common, I renewed the battery and clean all the earth terminals I could find, coating them with 'No-corrode'.
However, I just cleaned the actual terminals and did not think to check the crimping joints. If they are a "common source of curse", then they are certainly an area worth checking out. Running solder into the crimps is a very good idea.
Many thanks - you have certainly given me something to work on.
Regards
Dave

[J44EAG]

Don`t discount corrosion hot spots on the plugs and pins of the Power Train ECU module. I`ve had to deal with that myself due to similar faulting. Simply pulling off the plug and reconnecting a few times can be enough to restore good pin and plug contacts. Just one bad contact can be enough to really cause multiple issues of the type you are experiencing across several seemingly unconnected (slight pun) services on the car.

Mike K

[devans4004@aol.com]

Hi Mike,
Thanks for getting back to us again.
I've just purchased a crimping tool and some new terminals. Luckily it looks like there is enough wire to cut the old ones off and renew them.
However, your suggestion is certainly worth trying first.
I have some electrical contact cleaner and lubricant, so I can spray the pins as well.
Keeping my fingers crossed.
Regards
Dave

[RichardSEL]

No, my "TRAC NOT AVAILABLE" message on MFD doesn't come up on switching on IGN, just at starter motor turn
And then, not with a fully charged (aka just recently been on a long run) battery

Good luck with the crimps and battery leads -- can't harm and may help -- even a tenth of an ohm going back to the battery terminals could lead to 3V drop across it in either starter motor feed. Let us know how you get on?

[devans4004@aol.com]

Thank you again for your suggestions.
However, I have disconnected the ECU and cleaned all the contacts and sprayed them with a contact cleaner and lubricant. I have also re-crimped the 6 earth contacts by the battery, soldering them in the process.
Still exactly the same fault conditions.
Now I may be going mad, but I’m sure that once the engine got thoroughly warmed up, if you switched of the ignition, the coolant fan would go into overdrive, for a little while.
Although I have checked the fan and it is working whilst the engine is running, it stops the moment the ignition is switched off. Can someone please confirm if that is right.

[ptjs1]

Dave,

I had a slightly similar problem when I first had an x308 some years ago. When my car was just getting up towards the warm position, the gauge would jump up, then drop to zero and stay there and the car wold flash u restricted performance and other messages. It happened almost every day.

I changed the engine coolant sensor and the problem disappeared. I know that you've said that you replaced the sensor but a slight break anywhere in the wiring of that sensor, or a breakdown in its integrity when it gets warm, that could cause the same problem.

I'm a real advocate of never changing anything unless I absolutely know there's a fault with it. but I think I'd be tempted to do the following:

- When the problem happens again, immediately remove the wiring from the sensor and bridge the two plug terminals to see if the gauge goes to maximum deflection. If it doesn't, I think you may have a wiring fault. Perhaps even measure resistance reading of the sensor itself and report back with the figures.

- Try another sensor (I know that compromises my principle!) and don't buy it from anywhere other than a Jaguar dealer. There are lots of rubbish pattern sensors out there.

Good luck

Paul

[devans4004@aol.com]

Hi Paul,
Thanks for that.
It is certainly something that is easy to try although, if it is a fault with the wiring, I would have thought that I would have a problem whilst driving along, especially on the roads round here - potholes, speed bumps etc. She behaves perfectly, until left for a little while.
Can you tell me, when your XJS is thoroughly warmed up, if you switch the ignition off, do the fans stop straightaway.
I may be losing it, but I seem to think that mine used to go into overdrive for a little while.
I know that when a car engine is switched off, the coolant temperature rises. I am just wondering, if the fans should continue running to stop the engine compartment from heating up and screwing with the electronics. There again, I could be clutching at straws.
Thanks again.
Regards.
Dave

[PeterDavisX300]

Regarding the fans. I have an X300, and if I stop soon after a fast-run, or on a hot day, the fans remain on for a while. I've never timed the length of time, but having been used to this on a couple of my other cars I just took it for granted that it's ok.

[ptjs1]

Dave,

On my XJS, it uses a viscous fan on the main rad so doesn't run after I switch off. On my x308 and x350 with elec fans, I'm pretty sure they would only run after turning off if it was very very hot. At normal operating temp, I would expect the fan to cut off when the ignition is closed down.

As regards, the temp sensor fault, it was almost as if mine had a problem that when the resistance hit a certain point in the warm-up cycle, it would throw a spurious signal to the ecu causing the problem. The same situation could arise if you had excess resistance in the wiring loom, that the ecu could throw out when it suddenly thought it saw a particular out-of-range reading.

Paul

[devans4004@aol.com]

Thanks for that Gentlemen.
I was hoping I wasn't going mad.
I seem to remember, when turning off the ignition after a long run, the fans would seem to go into overdrive.
Wasn't sure whether it was a previous car though.
If anyone could give me further information on the cooling fans, I would be grateful.
I'll certainly try shorting the pins on the coolant sensor next time it happens; I have a piece of wire ready.
I agree with you Paul, I don't like changing anything until I have localized the fault to a specific component, and I would always use genuine Jaguar parts.
Thank you for your interest and suggestions.
Regards
Dave

[J44EAG]

Pauls description is very good and I agree with him.

I`ve had similar issues with both 4 litre V8 S-type and X350R which utilize similar ecu and sensors. On both cars at around 80K CHT sensors went duff. Identical symptoms on both. Spoof overheat condition, fans on, dash guage to full hot with red light on. Bad cold starts as the guage would be full deflection hot which caused the ecu to think the engine was full hot when in fact it was stone cold.

As said earlier in this thread, use only genuine sensor parts. I fitted an aftermarket CHT sensor which was totally unsuited to the car....it got even worse! The CHT sensor is a prime component. When duff it can cause big issues and curiously also cause diagnosis to imply the car is having a complete nervous break down! If in doubt, chuck that CHT sensor out!!

Mike K