TD5 electronic faults - any ideas?

My 2006 TD5 Defender refuses to start. I'd just pulled in to fill up with diesel and it failed to restart, although the engine spins freely on the starter.
Other symptoms include:
No engine check light or glow plug light on switching the ignition on. Temperature gauge goes straight up to hot, even with the engine cold.
What I (and the AA man) have looked at so far:
Fuses all seem OK; one was broken but that was just for the panel lights which now work OK (so that's one small bonus).
Inertia switch seems OK
Relays checked and passed muster.
ECU swapped with my spare and symptoms are the same.
If the ignition is switched on and the accelerator is repeatedly pressed, it does not enter a purge cycle.
No sound from the fuel pump.
No oil in the injector loom (though it wouldn't cause exactly these symptoms anyway).
Wires thoroughly wobbled and jiggled and tugged back and forth.

Any more ideas anyone?

I should add that neither my Nanocom nor the AA man's OBD machine could communicate with the ECU. There's just an error message saying 'failure to communicate with ECU'. That was true of both my ECUs.

Might be off the mark and no help as i know you have said you checked them but on my td5 the fuel pump relay would cause issues. The rely itself was fine, the spade terminals had been inspected and tightened up and seemed fine, but every so often the pump would not fire and a good firm wiggling of the rely would cause it to start again. Went through several new relays with no difference. Other than that i cannot be much help i try desperately to avoid things which aren't all nice easy mechanical bits.

Brown said:

My 2006 TD5 Defender refuses to start. I'd just pulled in to fill up with diesel and it failed to restart, although the engine spins freely on the starter.
Other symptoms include:
No engine check light or glow plug light on switching the ignition on. Temperature gauge goes straight up to hot, even with the engine cold.
What I (and the AA man) have looked at so far:
Fuses all seem OK; one was broken but that was just for the panel lights which now work OK (so that's one small bonus).
Inertia switch seems OK
Relays checked and passed muster.
ECU swapped with my spare and symptoms are the same.
If the ignition is switched on and the accelerator is repeatedly pressed, it does not enter a purge cycle.
No sound from the fuel pump.
No oil in the injector loom (though it wouldn't cause exactly these symptoms anyway).
Wires thoroughly wobbled and jiggled and tugged back and forth.

Any more ideas anyone?

Click to expand...

I had a similarish but not identical thing last week on my disco, testing for power to and from the inertia switch is a good start
https://landyzone.co.uk/land-rover/yet-another-hazards-inertia-issue.390500

dag019 said:

Might be off the mark and no help as i know you have said you checked them but on my td5 the fuel pump relay would cause issues. The rely itself was fine, the spade terminals had been inspected and tightened up and seemed fine, but every so often the pump would not fire and a good firm wiggling of the rely would cause it to start again. Went through several new relays with no difference. Other than that i cannot be much help i try desperately to avoid things which aren't all nice easy mechanical bits.

Click to expand...

Yes, years ago I had a fuel pump relay like this. I could change the engine note by wobbling it. Once the TD5 starts it will actually run without the fuel pump connected, just not very fast. I don't think it's a fuel pump relay problem in this case though, because that usually yields different symptoms.

Kev12 said:

I had a similarish but not identical thing last week on my disco, testing for power to and from the inertia switch is a good start
https://landyzone.co.uk/land-rover/yet-another-hazards-inertia-issue.390500

Click to expand...

Yes, when the AA man was looking at it last night he tried the inertia switch. "Nowt wrong wi' that" was the verdict Mind you, he was just testing with a device that lit up if there was voltage, rather than looking for resistance or the size of the voltage, so I'll have a look at that tomorrow with the multimeter when it gets light.

Thanks very much for the suggestions gentlemen. Keep 'em coming!

How about the little earth wire from the ECU?
Add an extra wire from the earth bolt to a good earth elsewhere.
I have a vague memory of reading about such a thing stopping the engine from starting and make the temp gauge go straight to hot.

Anaconda said:

How about the little earth wire from the ECU?
Add an extra wire from the earth bolt to a good earth elsewhere.
I have a vague memory of reading about such a thing stopping the engine from starting and make the temp gauge go straight to hot.

Click to expand...

I think someone has been there before us! A previous owner has cut their way into the black wires on the black ECU plug and run a lead to the battery terminal. I had half an hour before it got dark this afternoon and was looking for earth resistance between the earth sockets on the black ECU plug and a good earth point (nos 1, 2, 24 and 25 I believe) and they were all close to zero except for one which was about four ohms. Tomorrow I'll see if I can prize the plug open without butchering it and clean up the female 'shoe'.

It feels like the ECU isn't getting something it needs in order to activate. According to the diagrams I've got, it gets power in through pins 3, 22, 27 and 33 so tomorrow I'll check that those yield 12v too.

Blue plug under the seat box, it's a bundle of wires joined together. This can also cause your symptoms according to some lesser forums.

Anaconda said:

Blue plug under the seat box, it's a bundle of wires joined together. This can also cause your symptoms according to some lesser forums.

Click to expand...

Yes, it's some sort of header. I'll see if I can find a diagram of what's supposed to be joined together here.

A quick Google indicates that it's no. 0294. It doesn't look too complicated - it's just joining wires of a similar colour together.

Got to be worth giving it a go.

Anaconda said:

Blue plug under the seat box, it's a bundle of wires joined together. This can also cause your symptoms according to some lesser forums.

Click to expand...

+1, a swift heel kick to the seatbox and bounce around on the seat usually saw mine start

I had a look this morning and checked for a 12v live on the relevant terminals on the black plug (there's about three of them) that provide power to the ECU. There's nothing there. There's also an ignition switched live in another terminal, and that comes on. So I think the problem is that the ECU isn't getting any power. The fact that the ignition switched one is still working explains the fact that some of the functions are still operational but others (like actually starting the car) are not.

Yes, I had a look inside the blue header too. All looks nice and shiny and the wires are all firmly crimped into their terminals as if it left the factory yesterday.

Right, I've succeeded in starting the engine. The problem seems to have been an intermittent fault in the wire that activates the main relay. I bridged the load terminals on the relay holder with one of Xylia's hair clips and tried the ignition. Yes, sure enough a yellow engine light appeared momentarily. Emboldened, I turned the key further and the engine started.

Fortunately, the break isn't hidden deep in the wiring loom, it's right near the relay holder. In fact the wire came apart completely when I wobbled it. I'd like to fit a new relay holder and relay because the existing one is in poor condition, with the plastic getting brittle and cracking.

That's a good result, well done for finding it.

I'm just looking for a suitable relay holder to replace the old one. The original Land Rover item seems to be unobtainable, so i'm hoping that something like a Lucas Rists 51152073 will do the job. They seem to have a slot in the back so (if I'm lucky and it's the right size) I can mount them on the metal tabs on the inside of the ECU compartment. That way I can keep things looking fairly original. Loads of places sell the relay, so that's not a problem.

Finally, a couple of remarks about resources I used to help me.

http://www.lrworkshop.com is getting very good these days. Somebody's put a lot of work into that. I found it easier to use the circuit diagrams, connector diagrams and header diagrams off that than to look them up myself, even though I have a copy of the factory electrical manual. Plus they're in colour and I can screen capture, print them off in colour and take them out to the car as an aide memoire. I grew up on the cryptic black and white diagrams in manuals which were frustrating to use, but this makes doing electrical work on the car almost a pleasure.

Another thing I found useful was the document below which says what the pins on the ECU connectors do.

It says some of them are 'voeding' which I didn't understand - I don't think that's fitted on my model, must have been an option for the North American market. But it's a Dutch word that means 'nourishment'. Ah, maybe it's a live feed. Yes, that's what it was. The fuse in question that nourishes the ECU is no. 5 in the ECU compartment fuse box.