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Richard, ASE Certified Technician
Category: Australia Car
Satisfied Customers: 15556
Experience:  12 years Ford Lincoln/Mercury Jaguar dealership as a technician and shop foreman reparing all makes
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I have an electrical issue on my 2005 Jaguar X-Type 2l

Customer Question

I have an electrical issue on my 2005 Jaguar X-Type 2l petrol.Here are the symptoms. About 4 times out of 5 when I turn on the ignition, I get a "gearbox" fault message and the starter won't crank at all. Then, sometimes, if I leave the ignition on, the fault message will disappear and the ignition will return to normal. However when I then start the car (which runs fine) the battery light will usually stay on. When the gearbox fault doesn't appear, the car starts normally and usually the battery light goes off once started.The car has been to a specialist jag mechanic. They have so far:
replaced the battery
replaced the alternator with a second-hand one
replaced the alternator again with another second-hand one which they “reconditioned"
replaced the ignition switch.
Removed everything off the CANBUS except the engine ECU, transmission ECU and the JGate and the fault still comes up.
Replaced the JGate temporarily with another second-hand one to rule that out of the equation.Some other symptoms that are relevant:
when the gearbox fault comes on I am unable to put the car into neutral (there's a beeping noise)
last weekend when running in stop-start traffic the engine overheating light came on. I stopped and popped the bonnet and the fans were not running. The car definitely appeared hot, but once cooled drove fine to home.
The mechanics have checked the error codes, and the errors for the gearbox fault do not have a code against them (they're blank). So it definitely appears as though there are spurious errors happening.
there is an odd "whirring" noise when the ignition is turned on (sounds a lot like the test of the instrument cluster that you get if you switch into diagnostic mode). This didn't happen before the problem arose. On those occasions when the gearbox fault message disappears and the ignition returns to normal, there’s another sort of whirring/light clunk noise just before the message disappears. I’d describe is sounding like something is charging up and then reaches charge and everything returns to normal.The mechanic has tested the wiring loom and it all appears to test out OK - he tried to move it a bit in case there was a short somewhere, hoping that might make it obvious. But nothing.His theory is that it's either the transmission ECU or the engine ECU. He has a second-hand transmission ECU and is proposing he swap that in to see if the fault still occurs (as that's the easiest one to change and there's no programming required). That would then rule that in or out as the cause.If the fault still appears he says that would suggest the engine ECU to be the cause. That fits with the overheating issue before too (there's nothing wrong with the coolant levels - the fans just didn't start).The engine ECU replacement cost here in NZ is around $2500 for a new one and $1750 for a second-hand one. So, a very niggly, difficult to resolve issue.What I'm after is information I can give the mechanic so that he can isolate the problem. And feedback on whether you think his approach so far has been sensible. And lastly whether you’d recommend a new or second-hand ECM given the price difference. The mechanic did say that it can sometimes be tricky to reprogram the second-hand ones. It either goes well, he says, or goes pear-shaped.Thoughts?
Submitted: 2 months ago.
Category: Australia Car
Expert:  Richard replied 2 months ago.

Ok we have a few things going on here and I am not sure they are all related. Can I have the last six of the VIN so I can research this.

Customer: replied 2 months ago.
Hmm. Tricky to find the thing. But it was on the passenger side door pillar on my car.So I think the full serial number is ***** Does that look right?
Customer: replied 2 months ago.
Hi Richard. I showed the mechanic an earlier thread you'd answered with a similar problem ( and he'd done all the voltage testing you outlined in that thread. He thinks it's either the engine ECU or the wiring harness (or both) causing the issue.
Any thoughts?
Cheers. Mark
Expert:  Richard replied 2 months ago.

I think the problem is with the engine compartment fuse box. There is an internal slave ignition relay that provides power to certain modules and can cause a no crank no start then the battery warning. I have run into this on two other vehicles. We need to monitor power to the engine compartment fuses when the problem occurs in order to be sure.

Customer: replied 2 months ago.
Ok thanks Richard. I'll check with the mechanic and see what he's checked there and get back to you. Cheers. Mark
Customer: replied 2 months ago.
Could that also explain the overheating issue / radiator fans not kicking in?
Expert:  Richard replied 2 months ago.

This is usually the fan module itself which have high failures. It is only serviced with the fan assembly if you were going to use Jag parts.

Customer: replied 2 months ago.
Hi Richard.I've spoken to the mechanic and passed on your advice. He said he has checked the voltages at the fuse box and didn't see issues, but I'm taking it back in again on Thurs so he can re-check to make sure he didn't miss anything and then we'll post back the voltages he finds.CheersMark