Electrical help needed again

My 4 year old battery seemed not to hold its charge, so I did some investigation, put on a spare battery and that's when I noticed that the + terminal was getting hot when the engine had been ticking over for a few minutes.
Tried a short run and it was pretty hot along with the cable to the alternator and the cable that feeds the drivers seat fuse box
Did some investigation and found the glow plugs were pulling a high current when the engine was running.
Took out the relay and the current drops.
Went for a few mile run then parked up without stopping the engine, and the + terminal is now ok but the coil terminals on the black glow plug relay are live so if I put in the relay it would bring in the glow plugs again.

Need someone with a good understanding of the TD5 ECU to tell me what cuts off the signal from the ECU to the relay and shuts down the glow plugs?
Is it engine temperature? If so I may have a duff sensor

The glow plugs have a post heat operation with engine running too so the ECU keeps them under power untill the ECT input exceeds 20*C ... if the relay is powered beyond that then there's some problem

sierrafery said:

The glow plugs have a post heat operation with engine running too so the ECU keeps them under power untill the ECT input exceeds 20*C ... if the relay is powered beyond that then there's some problem

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Thanks for the reply
I took out the relay today and started the engine, it ran fine and the system voltage seemed to stay at 14.4 to 14.5 v so I went for a run about 7 or 8 miles then put the vehicle on the drive without turning off the engine, battery terminal was cool so that was good, but I tested the glow plugs relay shoe on the two coil terminals and they were live so if I had put the relay in it would have closed.
I need to re check but I'm sure during my tests today if I put the ignition on without starting the engine then the relay closed for a period but then opened again, seems strange it drops out with the engine off but holds in with the engine running.
I checked the contact blades on the relay itself and they are open when the relay is removed from the shoe

The pre-heat operation (without engine running) is timed out when the warning lamp goes out the when the engine is started IF the ECT input is below 20*C the relay is energised again untill the ECT gets above 20*C, that's the normal behaviour

sierrafery said:

The pre-heat operation (without engine running) is timed out when the warning lamp goes out the when the engine is started IF the ECT input is below 20*C the relay is energised again untill the ECT gets above 20*C, that's the normal behaviour

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I am wondering if the sensor is faulty and the ECU sees a false low coolant temperature and so re energises the relay when the engine starts.
I will try to order a new sensor and see if it makes a difference.

If the sensor is faulty or it's a problem on that circuit the temp gauge would show cold all the time... you need a tester to diagnose this

sierrafery said:

If the sensor is faulty or it's a problem on that circuit the temp gauge would show cold all the time... you need a tester to diagnose this

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The temp gauge seems to work very much as expected, so if its signal comes from the sensor it probably is working.
Let me try the nanocom and see if I can see anything which might explain.

You can monitor the glow plug relay's status with nanocom

So a new day
First thing put the battery on charge to be sure it's ok it didn't take long must have been nearly full.
Plugged in the nanocom and checked it, it gave the usual AC and brake faults but also one saying the load of the glow plugs relay was missing, cleared all.
Started up with relay removed, and ran for 10 - 12 miles, the coolant went up to between 88 an 91 degrees according to the nanocom.
Pulled onto the drive and stopped the engine.
Took out the seats replaced the relay, put the clamp meter onto the brown lead under the drivers seat which feeds the glow plugs relay.
Re set all faults with the nanocom.
Turned on the ignition and noticed the glow plugs did not energise.
Started up the engine (hot) and the relay did not pull in.
Battery terminal is cool after 5 minutes of running.
So it seems to work as it should and not like yesterday when it would not disengage the GP relay at all no matter what the temperature.
Left it for a few hours to cool down and repeated the start up test with relay plugged in, the temperature gauge showed about one third of the way.
Again glow plugs did not pull it and ran fine.

Seems the temperature will override the GP relay when the engine is warm and ignition is turned on.
Cant understand why it works as it should now, unless clearing the fault with nanocom did the trick.
I will try again tomorrow with the engine stone cold and the nanocom plugged in and see what happens.

Maybe it was a bad contact in the relay's socket and as the ECU didnthere are cases when relays are sticking too, better fit a new one to be ruled out... the code was most probably stored whne you drove it with removed relay hence the open

sierrafery said:

Maybe it was a bad contact in the relay's socket and as the ECU didnthere are cases when relays are sticking too, better fit a new one to be ruled out... the code was most probably stored whne you drove it with removed relay hence the open

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I ordered a new relay they are not expensive, I already had some of the yellow ones but they are not up to this load.
Also going to try and test the glow plugs one by one to see if any have gone down to earth.

I'm sure you are right about the code, but its really annoying to have something go wrong then goes ok and you don't know what exactly fixed it.
Worried it may do it again.

Thanks for posting. This is one eccentricity my TD5 has yet to demonstrate, but when it does I'll be ready for it.
The other thing that happens to TD5s as we've discussed, is that the wiring looms themselves deteriorate, but I believe you've renewed this recently or fitted a known good secondhand one. The glow plug gubbins is part of the red plug engine loom as I recall.

raywin said:

but its really annoying to have something go wrong then goes ok and you don't know what exactly fixed it.

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Yes, these kind of faults are the worst of all... you can wire in a LED to the GP relay's feed at least you'll always see if it works cos the warning light is managed by the ECU, it will work even with relay removed

sierrafery said:

Yes, these kind of faults are the worst of all... you can wire in a LED to the GP relay's feed at least you'll always see if it works cos the warning light is managed by the ECU, it will work even with relay removed

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That’s a good idea I need to do something like that to keep an eye on it.
Checked the glow plugs this morning
In situ number 4 seemed to vary sometimes reading 0.5 Ohms and sometimes 280 Ohms
All the others read about 280 - 300 Ohms but seems way too high using Ohms law to calculate the current the Amps is tiny
Took out No 4 and tested it it was about 0.6 Ohms which would pull about 20 Amps but of course that’s cold
So put it back and tried again
with No 4 connected the clamp meter ( not a good one) gave 60 Amps falling to 42 before the timer cut off
With No 4 disconnected then the clamp meter read 50 Amps falling to 32 before the timer cut off.
Started the engine with No 4 glow plug disconnected plug relay pulled in with the ignition then cut out on the timer, when it fired up the relay came back in and stayed in for about 40 to 55 seconds then dropped out, which seems normal behaviour

A new good quality glow plug should have between 0.5 - 0.9 Ohm resistance depends on brand

sierrafery said:

A new good quality glow plug should have between 0.5 - 0.9 Ohm resistance depends on brand

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Interesting assuming 12.5 volts would pull between 14 and 25 Amps when cold,
So would total 56 to 100 amps.
Mine seem much lower than that.
Better look for some, although its always been a pretty good starter.

The more I learn the less I know.
Took your advice and soldered an led onto some fine wire.
Poked the ends into the coil terminals of the relay shoe, (checked polarity)
Great a little white light beside my seat when the GPs are energised.
Worked fine comes on when you turn on the ignition, times out, then when you start the engine came on for about 3 seconds then went off, obviously engine is warm.

When you turn off the ignition and stop the engine the relay energises again for about 4 or 5 seconds, that had me confused.
Could they use it to pull down any charge in the ECU capacitors?
I still have the feeling that it's fixed but I could not explain why, but at least my battery terminal is not getting hot now, will leave the led in for a while and see what goes on.

Maybe i wasnt clear enough, the LED must be connected one side to ground and the other to the relay's positive output(feed to glow plugs) not to the coil, the coil is monitored by the ECU and it can be mixed up with other things in parallel

sierrafery said:

Maybe i wasnt clear enough, the LED must be connected one side to ground and the other to the relay's positive output(feed to glow plugs) not to the coil, the coil is monitored by the ECU and it can be mixed up with other things in parallel

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Ok I will swap it onto the contact and ground the other side, so it could be the ECU signal monitoring the coil which lights the LED, didn't expect that.
Greased the UJ s on the propshaft just to do something straight forward.

Did the LED today, and my new clamp meter arrived.
I checked the feed to the GPs and they definitely come in for a few seconds when you turn off the ignition to stop the engine, that seem strange to me, but the rest of the time they seem normal, i.e turn on the ignition and they come on, time out and go off, then when you start the engine they come back on and drop out with the coolant temperature (I assume).
One thing I was thinking was to re install the ECU map and see if it behaves the same way.