ECU known failure points

[gmac78]

Alright gents,

As some of you may know, I recently had an ABY ECU failure which happened randomly whilst cruising along at around 60mph.

Prior to this occurring I hadn't jump started or used a battery pack booster , battery terminals were tight, and I am still using the OEM alternator with a 150K on it. Voltage regulator seems to do it's thing with around 13.8-13.9v at the alternator ( is this acceptable or should I be getting around 14.4v?), slightly less at the battery but to be expected I guess and never had any battery draining issues. These figures have been taken after the failure with use of a working replacement ECU.

So, from issues others have had with an Over voltage diode (D901) collapsing and going to ground, I removed mine from the ECU for testing which appears to be fine. The act of simply removing it (if it was grounded) should allow the ECU to be powered up again, all be it with no further over voltage protection. However for me there was no difference with the diode removed. It would still blow fuse 27 when the ignition was turned on.

I see others have sent their ECU away for testing, however from the places I have tried so far they don't recognise the ECU part number as one of the ones they can test but will have a look at it anyway with no guarantee of repair. The quotes for a successful repair are silly money, one I tried was £320 plus VAT and another £220 plus VAT. I purchased a replacement ECU for cheaper than this so reluctant to spend that kind of money on a repair considering it's probably a component that costs less than a £1 to replace!!!

With that in mind, what other components of the ECU have been known to fail in the past and how is best to test them?

I'm determined to get to the bottom of this issue and get my old ECU up and running again since it already has the upgraded MAP sensor and R201 mod which I require for my RS2 based software.

Hope you fine gentlemen can assist with this issue, got to be some electronic gurus out there!!

Cheers chaps.

[Greg_S]

You may be better getting it to an old school auto electrician or electroncs repair specialist who can review the components as most modern ECU's will be inspected via software I expect.

[gmac78]

Yeh I got the impression from several places that I contacted that if they couldn't plug the ECU into some kind of bench testing facility they weren't interested. Like you say, surely some type of electronic specialist would be able to track down the failed component with relative ease??

[Nuvo]

I'd be checking for another short circuit in the vicinity of D901. A schematic diagram of the ECU has been posted on the forum if you can find that it will help.

edit: You can grab the schematics from here.
Look at page 2. Keep a look at the left side of the page and you'll see pin 19 (Gnd) and follow that to find D901.

[gmac78]

I'd be checking for another short circuit in the vicinity of D901. A schematic diagram of the ECU has been posted on the forum if you can find that it will help.

edit: You can grab the schematics from here.
Look at page 2. Keep a look at the left side of the page and you'll see pin 19 (Gnd) and follow that to find D901.

Evening Nuvo,

That's coincidence that you would post this, as I was just having another look at the ECU.

I decided to go round all the diodes with my multimeter on the hunt for any suspicious readings, and I think D900 might be the culprit as it appears to be shorted out. This diode is uni-directional so I believe I should only get a reading going in one direction, however when I test it with my meter it shows a dead short in both directions. D901 which was the diode I removed previously is a Bi-directional diode, from what I gather I should not get a reading in any direction on this if it's in good condition which was my findings.

Cheers for the schematic link, very handy!! I'll have another look at this tomorrow when I'm not so tired , had my Covid vaccine this morning and been feeling like I need to sleep all day. Time for bed now. Fingers crossed this is the cause of the problem. Cheers mucker.

[gmac78]

Evening all, I removed diode D900 (BZW0619) from the ECU and can confirm it's shorted out. New pack of diodes ordered so hopefully a nice cheap fix?

[newsh]

Evening all, I removed diode D900 (BZW0619) from the ECU and can confirm it's shorted out. New pack of diodes ordered so hopefully a nice cheap fix?

Good news! Well done ?

[John.]

Evening all, I removed diode D900 (BZW0619) from the ECU and can confirm it's shorted out. New pack of diodes ordered so hopefully a nice cheap fix?

Hat off to you, your perseverance has paid off

[gmac78]

Alright gents, how are we all?

Just an update on this issue, I'm still waiting on the first diodes I ordered to turn up, however after testing diode D901 it appears to working fine so I decided to reuse the original one and just replace the one that was blown (D900) which I now have spares for.

Yesterday I finally got round to soldering these back in and pleased to say the ECU is back up and running, no more blown fuses, car started first time and idles perfectly. I've got the propshaft off for overhaul so no drive at the moment to test it out but all appears as it should be.

So in conclusion, anyone that has an ECU issue where it blows fuses 27 & 28 should focus on these two diodes which are right beside one and other. They can be tested in circuit so no need to remove them for checking. I am by no means a soldering expert but bought myself a new fine tip for my soldering iron and some good quality leaded solder from RS components which seems to have done the trick. It was quite tricky to solder on to the PCB board with tracks close by so just be careful not to damage these if you tackle this yourself.

All in all I'm glad I tackled this, as the money some of these ECU repair places were charging was just a rip off in my book, especially when the diodes to carry out the repair cost pennies!!!

Thanks for all that helped me out with this matter, much appreciated.

[simons2]

Excellent , thank you for sharing

[Chris5044]

thank you for doing this!! this is highly liking the cause of my original oem ecu failure. I still have it! so perhaps I may be able to repair this as you said.. as its blowing the over voltage diode and those fuses 27 etc.

[S4Philk]

Wish I'd come on here before testing my ECU. Just found my diode between pins 18-19 has failed, shorting fuse 27 on my 3b to the number 19 earth pin.

Seems to be a common problem with a simple fix. Now to find the right diode.

[oollit]

I also have this problem with an ABY ECU, I have tried a non immobiliser ECU but the fuel injectors aren't firing so starting to think the replacement ECU is faulty too, but can't just keep on buying ECU's so think I will have a go at trying to repair the origonal ECU.

When I view the tagged scematic I just get blank pages, any chance of you uploading a photo showing which one of the diodes was blown so I know where to start looking.

[gmac78]

I think the same happened to me when I first tried to open it, managed to get it working in the end, can't remember how though. Try this mate, I still had the schematics saved on my laptop.

[oollit]

Thanks, I can open that one no problem.