Audi A4 climate-control tip - Aprilia
A4 owner (1.8 1997) got in touch with me regarding a problem with his climate control. The stepper motors had stopped moving (not good at this time of year). Audi dealer charged him £75 to look at fault codes and told him ECU was U/S. £700 P+L repair estimate.

He got a secondhand ECU for £80, connected it up and it too didn't work.

I had a look at the secondhand unit's PCB and found three dry joints where the ribbon cable goes to the control keys. Reflowed the joints and, hey-presto, it works.

Looked at the other (original) faulty ECU and it had the exact same problem. It too was repaired. He's keeping it as a spare!

Obviously a common problem and worth A4 owners remembering it.
Audi A4 climate-control tip - 659FBE
Aprilia, It sounds suspiciously as though we may have similar automotive backgrounds. My speciality was diesel engine electronic governing.

The problem you describe with the Audi ECU is not caused by dry joints, but by solder fatigue causing broken joints. Solder is about the worst substance imaginable in fatigue - note what happens when you bend a stick of solder a few times.

If an electronic assembly has no stress relief in the joints and is thermally cycled a few hundred times, as will happen in automotive equipment, the joints will fracture. Next time you see one of these, take a look with an eyeglass at the joints before you reflow them. There will be the classic signs of fatigue, indicated by a frosted crystalline appearance to the edges of the break. A true dry joint would not wet the copper on one or both surfaces.

This problem is hard to overcome unless very great care is taken to avoid stresses in the components and pc board, brought about by differing coefficients of expansion and a lack of flexibility. For instance, a standard dual-in-line integrated circuit is highly prone to this problem due to its rigidity in the board. I spent many hours on this problem, and there are solutions, but most manufacturers of electronic assemblies seem to be blissfully unaware of this difficulty. It seems that thermal cycling is not a part of their development testing.

Regards, 659 - ex Prince of Darkness.
Audi A4 climate-control tip - Aprilia
Yes, I'm pretty sure the joints had indeed fractured just as you describe. I used the term 'dry joint', rather loosely and inaccurately in my post, as a 'generic' term for the failed joints.

I too worked on automotive electronic systems. At one point getting involved in parts of the design and production of MEMS ECU's (Motorola manfr.).

Obviously I'm aware of your ex-employer. I used to know some of the guys there (Advanced Engineering Centre) quite well, especially in 'Sensors and Actuators' (Steve Prosser?). IIRC your co. were planning on looking at all the issues around PCB solder joint reliability in automotive applications and they did put together some kind of research proposal around 1993-5 time? But I don't think it ever went ahead. Is that right? A lot has happened since then, Varity, TRW etc. I even got offered a job there in the AEC around that sort of time, but didn't fancy working in that great big open plan office area. They had some good ideas. There was a guy with a slightly unusual name working on a autonomous cruise control system with road marking recognition. They rigged up a Jag XJ6 with it and it would keep itself within a lane on a motorway without the driver touching the wheel. I still have a video tape of it somewhere. Lots of good ideas, but not many made it to market....
Audi A4 climate-control tip - 659FBE
Aprilia, Company identification spot on - I knew Steve Prosser.

In order to be helpful to the good readers of this site, I thought about compiling a list of ECUs at risk from this problem, but decided in the end it would be wiser to keep my comments very general, so here goes:

Units generally free from these problems are those not involving printed circuits, but using thick film technology. Examples are voltage regulators on alternators, and most ignition modules, but not coil assemblies, from the larger manufacturers.

ECUs with potential problems are the more complex units using printed circuits, mounted in the engine bay and made by the less experienced manufacturers. Bosch generally have this problem under control, apart from the odd cock-up, as do the larger Japanese producers. Amongst the worst offenders are the non-specialist French, Italian and East European makers, which some vehicle producers fit in order to avoid paying Bosch prices. The cheapest of the wholly German vehicle builders have sourced from East Europe with some problems. I am very sorry to report here that I find the American, and what is left of the British producers are completely clueless.

I would be interested to hear of your experiences, my conclusions are to buy Bosch or Japanese. Bargains are there to be had - I have a Peugeot diesel with Bosch engine management. Pity about the rest of the electronics. Regards, 659.

Audi A4 climate-control tip - DL
Thanks for the tip, 659....hopefully I'll never need to use it.....
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Audi A4 climate-control tip - 659FBE
Aprilia's tip, not mine. 659
Audi A4 climate-control tip - Aprilia
Yes, quite agree with your comments - Bosch or Japanese.

Have you ever come across the 'flexible ECU's' - I saw a Detriot Deisel unit. It was a 68000-based ECU built on a flexible multilayer PCB. The thing just folded up to make five sides of a box and dropped inside an aluminium housing - most peculiar. I was told that they are very reliable!
Audi A4 climate-control tip - DL
Doh! Too much seasonal cheer plus a Pop-Idol overload tonight!

Cheers both...
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Audi A4 climate-control tip - Ian Chandler
I was intrigued by this post because I too have an A4 with a dodgy climate control unit. Sometimes the display comes on, sometimes it doesn't light up at all; sometimes it lights up but the numbers don't show.

This is quite probably the connections that Aprilia describes - I had suspected something like that. But are they easy to fix? Do I just need to take the box out, put it on a bench, open it up and then spot and put solder on any dodgy joints? Or is it more difficult than that and are there pitfalls awaiting an unskilled electrician like me?

Audi A4 climate-control tip - DL
The joints will surely be very small - any error here and you've waved goodbye to the unit.

I think you'll need soem fairly precise soldering kit plus an experienced hand!

Perhaps Aprilia could start up an exchange unit service??
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Audi A4 climate-control tip - 659FBE
Aprilia, I have not seen this particular ECU, but I have examined other American fold-up flexies. The problems with all of these are that multi layering of the board is difficult in order to give a reasonable component density, plated through holes are generally not good, exacerbating fatigue problems and terminations to connectors are notoriously unreliable. The pc flexibility does not automatically improve thermal cycling performance, and can lock-in stresses. Flow soldering of flexies in production can be interesting...

Big diesel ECUs are generally packaged with the engine - the one for Cummins PT system is on a heatsink cooled at the back by the incoming fuel. What our friends have forgotten is that the temperature of the whole assembly shoots up on soak-back when the engine is stopped. The thermal performance of this package when fitted, say, to a bus is abysmal.

Do you remember where VW sourced the Audi heater controller?

I would be interested to hear of any other ECU failures which could be attributable to thermal fatigue.

Looks as though another has just appeared whilst writing this offline. 659.
Audi A4 climate-control tip - elekie&a/c doctor
BMW E36 3series suffer with similar problems on climate control panel .poor solder joints on pcb .They are repairable but at least BMW offer an exchange unit at around £170 far more acceptable than Audi £400+.
Audi A4 climate-control tip - Aprilia
Tell me about it...

I had a climate control unit go wrong on a 7-series. Sadly it wasn't just bad joints, the CPU (AKA microprocessr) had failed. Unfortunately they couldn't get me an exchange unit and a new one was about £600. I managed to get one off a write-off for about £100.
BMW have also had lots of problems with faulty instrument packs. It seems that the top of the dash gets very hot in the summer and 'cooks' some of the electrolytic capacitors in the instrument pack, leading to their failure. A fairly easy repair if you know what you are doing, but I gues many customers end up paying ££££ for a new unit.

The PCB's on these ECU's (Audi, BMW etc.) are quite intricate affairs, you need to know what you are doing. I have a solder station which cost about £600 a couple of years ago, it is designed to tackle intricate work on SMD boards. It is suitable for this sort of work - I have repaired camcorders, PC motherboards and quite a few ECU's. Don't tackle this sort of thing if you only have an Antex soldering iron bought from Maplins - you'll do more harm than good.
Audi A4 climate-control tip - Deryck Tintagel
I'll not say too much at this point but Steve Prosser is still with TRW.

Good to see more automotive electronics engineers about :-)
Audi A4 climate-control tip - Aprilia
Just looked at your profile. Very interesting. We may have met at some time if the past. EPAS........(on a Corsa?).
Audi A4 climate-control tip - Deryck Tintagel
Not on the Corsa: EPS on models released in the last year or two. Can't say too much ...
Audi A4 climate-control tip - Ian Chandler
Aprilia, you've told me what I rather suspected about trying to fix this myself. A small soldering iron and a length of solder was exactly what I would have tried. However, do you have any bright ideas on where I might find co-operative people with the kind of precision soldering equipment you describe? Would TV engineers do this sort of thing?

Incidentally, if an Audi aircon system does play up it isn't necessary to go to Audi to read the fault codes. There is a way of making them appear on the display of the climate control unit - and the key to the codes is available on the internet. I think I found it once on a site for GTI owners.
Audi A4 climate-control tip - Aprilia
Aprilia, you've told me what I rather suspected about trying to
fix this myself. A small soldering iron and a length of
solder was exactly what I would have tried. However, do
you have any bright ideas on where I might find co-operative
people with the kind of precision soldering equipment you describe? Would
TV engineers do this sort of thing?


Yes, if you can find a friendly repair guy who is used to repairing modern VCR's and camcorders etc. they he is likely to have the kit and the experience to help you. Its always worth a try if the unit is non-functional, especially if on a 'no fix, no fee' basis.
Incidentally, if an Audi aircon system does play up it isn't
necessary to go to Audi to read the fault codes. There
is a way of making them appear on the display of
the climate control unit - and the key to the codes
is available on the internet. I think I found it once
on a site for GTI owners.


Yes, I know you can get the codes without going to the dealer. I have 'chapter and verse' on it. Unfortunately the guy who had the fault only came to me after the codes were pulled and when the dealer virtually asked for a blank cheque before taking on the repair.
Audi A4 climate-control tip - Ian Chandler
Thanks a lot for that. My aircon is still working, if a bit dodgily, but when I have a bit of time and the weather is better I'll have that box out and take it along to one of the local people who have a small workshop and do that kind of thing.
 

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