Stroppy Freelander

[Jojo]

My better half's FL throws a tantrum again. The engine warning light comes on intermittently, with a resulting drop in performance as the engine presumably drops into limp mode. Turn off the beast and on restart the warning light is off, until it reappears unexpectedly at some point later.
The other issue is that the vehicle has become difficult to start, i.e it needs cranking over for quite a while before it fires up, even when warm. When enquiring, wifey told me it has been doing this for a while (why she never mentioned anything about it remains a mystery). So far, so good. On investigation today I found that the pre-heating system doesn't work at all (!). So, this explains the starting trouble. The pre-heat dash light doesn't come on, the relay doesn't actuate. The fusible link and the fuses in the engine bay fuse box are alright.
I haven't got any further as time and low temperatures prevented any further investigation and remedy attempts.
Now, where should I start to sort out the problem? Am I right that the engine warning light might have to do with the starting trouble? What is the likely cause of the problem? The glow plugs themselves? The coolant temperature sensor (the temperature gauge works)? Why doesn't the preheating indicator come on at the dash? If the problem is glow plug related, why doesn't the car start easily when warm?
It's a 2004MY Td4, btw.
Grateful for any advice!
Cheers

[woko]

With the engine light coming on there should be a fault code logged. Have you got the fault codes read?

Low fuel pressure can cause this issue.

On the early TD4 there are 2 electric pumps 1 mounted in the tank and one mounted in the engine bay. I think the later ones only had 1 mounted in front of the RHR wheel. I could be wrong though, its been awhile, there may be 2.

It would be worth checking the tank unit as this is common symptoms for early TD4 non start. There is a cover plate under the RHR seat carpet to access.

Also wiring/plug to the fuel rail pressure sensor is common to corrode.

I wouldnt worry to much about the glow plugs at this stage as they will only operate if the engine ECU deems it necessary.

[Jojo]

So, now we have been able to narrow down the problem. It appears to be a fault in the ECU as it is not activating the glow plugs. The plugs and the relay are fine, as are all the connections and wires.
There were some unspecific fault codes logged, presumably a result of the drained battery and futile starting attempts.
Anyone here who had a similar experience? Anyone who knows if the ECU can be "reprogrammed" or do I need a new module? How much are they???
Those modern vehicles are just soooo confusing...
Cheers