How I fixed my TD5 ECU (maybe worth doing for preventative reasons too)

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BulletBrindle

Active Member
Posts
105
Location
Worcestershire
May 22 update - my ECU stopped working, so there must be something wrong with it beyond the big caps

***Just because this worked for me, doesn't mean it will for you. This could wreck your ECU permanently***

Thanks to eprothe for the inspiration - https://www.landyzone.co.uk/land-rover/ecu-problems.366226/page-2

If you're going to give it a try, please read the whole thing before jumping in and check out the photos...

I thought I put a quick post together to describe how I fixed my own ECU, in case anyone else wanted to give it a try on their own one. As these ECUs are getting quite old now, it may be a good preventative measure to do on working ones too.

A quick bit of background - my ECU failed last year with two errors codes - Topside switch failure and injectors 1-5 open circuit. Basically, the engine would crank, but no fuel was being injected. Fortunately, I sorted a spare ECU without any trouble, which kept me going for the past few months, and the broken ECU just sat in the cupboard.

I decided that I really should try and sort out a spare ECU, as I really don't want to get stranded again, especially down some green lane in the back end of nowhere.

I leant that it is usually the two big caps that fail, so I thought replacing those was a good place to start. After much searching, I managed to find some suitable capacitors with proper screw terminals and mounting studs, one of which is a perfect drop-in replacement, and another which will fit with a little effort/modification (nothing too drastic, I promise).

The 100V cap is a Kemet PEH169PA4100QB2 and the 40V is a Kemet PEH169KA4330QB2. Places like Mouser or Digikey resell these. Watch out for lead-times...

The first step is to get the cover off and inspect the PCB. There are 4x torx security bots to remove, which is the easy bit, and you then have to pry off the top cover, as it is held in place by some kind of sealant. I don't have a good way to do this - I think I just worked my way around with a large flat blade screwdriver. Undoubtably there's a better way, but I don't know what it is.

Once inside, you need to thoroughly inspect the PCB and the smaller components. If there are any signs of charring of the PCB or damage to any of the smaller components, then I doubt this will work for you. Fortunately, my PCB looked brand new.

If yours looks good too, then the next challenge is to remove the two big capacitors. Firstly you will want to make sure both caps are fully discharged - I'll let you decide how to do this, as I won't recommend what I did.

Once your caps are discharged, then remove the large nut the holds it in place and then start to undo the 4 small bolts at the front of the caps. You won't be able to undo them all yet...

The next step involves the first permanent modification of the ECU - you need to cut out a piece of metal that the big mounting stud on the cap currently passes through. I found that with some snips I was able to cut out enough metal to free the cap from the mount, but still leave enough metal there so that I could mount the new cap in the same way.

Once done, you should then be able to lift the caps up, which will give you enough movement to finish undoing the small bolts at the front of the caps. Once the caps are fully removed, unless the small bolts and locking washers look pristine, I would discard them and buy new ones (mine were corroded and/or dirty). Replacements can be bought from screwfix for less than a fiver (I used M5 x 8mm bolts, but I think the originals were M5x 10mm).

I would recommend giving the 4 contacts that the bolts pass through a good clean before reassembly.

The new 100V cap can now be installed. Makes sure that the positive terminal is located in the right place, and then fix it in place (don't forget the lock washers). Getting the new mounting bolts to bite into the threads on the cap can be a bit fiddly, and you may well find that you have to bend the metal mounting 'frame' that surrounds the caps. I found that holding the whole ECU upright so that the bolts were screwing downwards into the caps was the best way. Once you've got them both to bite, then it should be just a matter of doing them up and then sliding the mounting stud into the slot that you cut.

Installation of the 40V is a little more challenging, as you may have noticed that it is a little longer than the old one that you removed. This is where the next permanent modification comes in - you need to snip off a plastic '+' shaped stud that projects from the front of the mounting frame below the two contacts. Then, with some needle nosed pliers, I bent both the front and rear sections of the mounting frame to make the opening for the cap a bit longer - take it easy with this bit, as you don't want to break any of the legs away from the PCB. Do it little by little, offering up the cap to check if you've got enough space yet.

Once it looks like you've got enough space, now is the time to try and get the small bolts to bite into the contacts on the cap (lock washers!) Once done, then it is a case of tightening them bit by bit, and sliding the mounting stud down into the rear support (you may need to bend the support backwards with the pliers while doing this). Once in, then fully tighten all bolts and nuts on the studs (don't over do it here).

Makes sure there is no debris inside, and then pop the lid on temporarily.

That should be it. Time to give it a try!
 

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This is a great thread.:):):)
I read it with interest as I had a perfectly good working ECU which went fubar after I dropped it on some gravel while cleaning the oil out of the red plug.:rolleyes:
I sourced another from eBay and once I took it to a garage to get it to talk to the rest of the car, it has worked fine since.
But the original one had been remapped before I got the vehicle so I wanted to put it back in.
I gave it to a relation who knew a lady engineer who was a very wise woman, she examined every connection with a special microscope but could find no problems, no physical breaks nothing.
So I am now wondering what codes I might get if I put it back in and with my Foxwell connected to see if it'll tell me what the problem is. ;)
But on another note, capacitors do seem so often nowadays to be a problem.:(
I have thermostats for under floor heating in France three of which have failed and the one i looked at closely seemed to have a capacitor problem on looking at where it connects to the rest of it.
Ditto a problem with a capacitor on a dishwasher.

Looking forward to hearing the results of your trial!:):):)
 
"Firstly you will want to make sure both caps are fully discharged - I'll let you decide how to do this, as I won't recommend what I did."
The last one I discharged was for an air conditioner compressor. I had a box of them under the bench that i kept as spares. When i grabbed one it bit me...
HARD! Ooh did i yelp!
I was surprised it had any charge left in it considering the last one i had dropped in the box had been a couple of months previously.
The easiest way to discharge one is to bridge both terminals with something other than your flesh!
After that one bit me i used to place both terminal spades onto my metal bench before puting it into my spares box.
 
"Firstly you will want to make sure both caps are fully discharged - I'll let you decide how to do this, as I won't recommend what I did."
The last one I discharged was for an air conditioner compressor. I had a box of them under the bench that i kept as spares. When i grabbed one it bit me...
HARD! Ooh did i yelp!
I was surprised it had any charge left in it considering the last one i had dropped in the box had been a couple of months previously.
The easiest way to discharge one is to bridge both terminals with something other than your flesh!
After that one bit me i used to place both terminal spades onto my metal bench before puting it into my spares box.
I was once dismantling a large and very heavy old colour TV. so old it didn't have a remote. It hadn't been used for ages.
I just wanted to make it more moveable so i could take it to the dump without breaking my back.
I took a pair of snips and cut the cable between the capacitor and the tube.
SH!T, I thought i had had a heart attack. The pain shot across my chest. I think my left hand was holding the frame or something.:eek:
It was a big bugre, about the size of a coil on an older petrol car engine.:eek::eek::eek:
 
I was once dismantling a large and very heavy old colour TV. so old it didn't have a remote. It hadn't been used for ages.
I just wanted to make it more moveable so i could take it to the dump without breaking my back.
I took a pair of snips and cut the cable between the capacitor and the tube.
SH!T, I thought i had had a heart attack. The pain shot across my chest. I think my left hand was holding the frame or something.:eek:
It was a big bugre, about the size of a coil on an older petrol car engine.:eek::eek::eek:
You are lucky. People have been killed by those old TVs when they have discharged on of the old capacitors!
 
You are lucky. People have been killed by those old TVs when they have discharged on of the old capacitors!
Having gone through it I can quite believe it!:eek::oops:
Shame it didn't come with a govt health warning!!!
Mind you it prolly did have summat on it like "don't go in here unless you are a pro" but I was just ignorant and in a hurry!
Nice to know I have a charmed life!!!:D:D:D
 
Bit of an update (sadly)

The 'repaired' ECU failed today on the way home - same fault as before, I believe. Fortunately I had a spare with me, so back up and running in no time.

Must have got over 1000 miles out it before it went, but went it did.

If I can't get it to work again, I think I'll just buy a spare. The current one is an NNN000120. Does anyone know which other models will work OK? As it'll only be a spare, I'm not fussed about everything working perfectly, just well enough to get me home.

Cheers
 
For spare to get you out of trouble you can get any of the followings: MSB101170, MSB101171, MSB101360, MSB000080 make it learn the security code, set to 2 way throttle and the defender will run nice with it even if your's is Eu3... i fitted a MSB101171 to a friend's 2002 defender when his NNN000120 failed and he was so pleased that he kept it for good
 
For spare to get you out of trouble you can get any of the followings: MSB101170, MSB101171, MSB101360, MSB000080 make it learn the security code, set to 2 way throttle and the defender will run nice with it even if your's is Eu3... i fitted a MSB101171 to a friend's 2002 defender when his NNN000120 failed and he was so pleased that he kept it for good
Thanks. Do you know which of the NNN models will work too? I know to avoid the ones from Discovery Automatics, but that's all I know.

Cheers
 
On Defender the only NNNs which are OK are the 000120 and 500020 with the condition to be loaded with a Eu3 Defender fuel map not D2 or Eu2 otherwise they work worst than the MSBs i mentioned which are all dedicated for Defender and work well with the green injectors too
 
A common failure on these ECU's is the tiny surface mount resistors around the smaller microprocessor chip near the top of the PCB.

They are in groups of 4 and if one fails, the engine will just stop. The temperature gauge won't read, there will be no EML and no glow plug light. The fuel pump won't run but the engine will still turn over on the starter.

lf this happens to yours, it's repairable but you'll have to send it off to someone who does TD5 ECU repairs.

The surface mount resistors can be bridged with normal resistors so it's a fairly straightforward repair.
 
On Defender the only NNNs which are OK are the 000120 and 500020 with the condition to be loaded with a Eu3 Defender fuel map not D2 or Eu2 otherwise they work worst than the MSBs i mentioned which are all dedicated for Defender and work well with the green injectors too

I'm going to try and source one of these NNN types to have as a spare. If I get one from a Discovery, is there any way to get the temp guage to work the right way round for a Defender? Cheers
 
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A common failure on these ECU's is the tiny surface mount resistors around the smaller microprocessor chip near the top of the PCB.

They are in groups of 4 and if one fails, the engine will just stop. The temperature gauge won't read, there will be no EML and no glow plug light. The fuel pump won't run but the engine will still turn over on the starter.

lf this happens to yours, it's repairable but you'll have to send it off to someone who does TD5 ECU repairs.

The surface mount resistors can be bridged with normal resistors so it's a fairly straightforward repair.

Are you referring to the ones circled in the attached photo? I don't have the skills needed to test or replace these myself, but a few people at my work are able to do this kind of thing. Cheers
 

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A failure of one of those would end up in a "checksum error" rather than "topside switch failure"
I've not been able to check the fault codes for the second time it failed, so they could well be different this time. Sounds like I'd be wise to borrow a Nanocom sooner rather than later then
 
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