ECU repairs

Stempy · Post by **Stempy** » 28 Jun 2009, 15:58

Ever since I've had my AX and sorted all its initial issues I have had the feeling that it wasn't quite running as well as it could. I've never expected it to be any more than what it is but I had a niggle in the back of my mind that the engine wasn't running as smoothly as it could do.

Having been through all the usual checks with fuel delivery and ignition I decided to pop open the ECU and there staring me in the face was a solitary 100uF 40v electrolytic capacitor.

Now having been in the A/V industry for more years than donkeys have, I have come to suspect these little items for causing untold havoc in every bit of kit you can imagine. The problem is that after a few years the electrolyte dries out and renders them incapable of doing their job, and quite often they will also leak said electrolyte all over the PCB.

This particular one hadn't leaked but had in fact dried out, replacing it has given the AX a new found smoothness and an improved throttle response. This got me to thinking that if any of the ECU's in the Xantia use simailar components then they could be responsible for all sorts of weird and wonderful faults with suspension, autobox etc. To this end I will be making investigations and will report back what I find, as this could explain some of the strangeness I have with the V6.

JamesQB · Post by **JamesQB** » 28 Jun 2009, 17:47

Interesting topic. I read a few years back an article by an ECU repairman. He said that 95% of the ECUs he received were suffering from dry-joints, and that was the primary cause of their issues. I wouldn't be surprised if many of the rest were suffering electrolytic problems. Although my father's trade was electronic repair, something which is still carrying on through my brothers (and me, until a couple of years back), I used to fear opening ECUs because of the replacement cost. I lost that fear after reading the article and realising that they're just another piece of electronic equipment and nothing special (which they really aren't).

I've since opened, resoldered and checked electrolytic value and ESR in a few ECUs and will continue doing so. As you say, electrolytics are always trouble, and in a hot engine compartment inside a sealed unit they're going to dry-out over time. I wonder how many ECUs have been replaced at a cost of hundreds simply because of simple component failures like these?

SMD tantalums are proving just as troublesome in small-scale devices like laptops - once they get too hot, they fail short. Had a few which have done this and they often take out the buck converter MOSFETs too, which are very hard to source but only cost a pound or so each.

Computerisation of cars has been both a blessing and a curse; whilst achieving better response, fuel usage, etc., we now have the scourge of multiple problems cause by hardware and worst of all, software, the biggest evil of them all. Not to mention how hard it has now become to find the cause of faults because of it (unless you happen to own the expensive and correct type of interface).

Be interesting to see how the V6 goes...

Post by **CitroJim** » 28 Jun 2009, 20:00

Well done Stempy

As James says, electrolytics are the No.1 source of all sorts of electronic troubles. They always have been and I guess they always will be. As for tants, well they're just dangerous. There myust be a better way..

I've had a 4HP20 gearbox ECU open a nd I cannot recall any electrolytics in it.

What are the "funnies" you're having on the V6?

Stempy · Post by **Stempy** » 29 Jun 2009, 00:12

The funnies are one with the suspension and one with the autobox. I think I mentioned before that it can grab 1st gear quite violently sometimes and I'm sure it's telling the engine management to reduce power in 1st too.

With the suspension it will on occasion rattle the rear electrovalve when turning off the ignition. Or at least that's what it sounds like, a kind of machine gun like sound.

Post by **CitroJim** » 29 Jun 2009, 19:14

Tell me in great detail the circumstances in which it grabs 1st gear please Stempy and precisely how it does...

The gearbox ECU deliberately reduces engine power by artificially retarding the timing under certain gearchange sequences. Have you a copy of the 4HP20 training manual as it expains it in there. If not, PM me. It's a seriously good read, especially the chapters on the gear changing laws...

I'd say the rattling rear electrovale is a sign the diode is a bit fluffy. Mine did much the same on occasions until I did the diode mod. In fact that's how I determined primarily that the diodes were needed.

How long since you've had your car on a Lexia? I'd be inclined to re-initialise the aut0-adaptives on your autobox ECU so it is forced to re-learn the valve block and 'box character.

I'd also look for stored hydractive faults and clear them after doing the diode mod if youv'e not already done so.

Stempy · Post by **Stempy** » 29 Jun 2009, 19:34

Well it goes like this, when slowing to the point where 1st would be necessary, whether braking or not, then reapplying the throttle, rather than pulling away smoothly it'll let the engine revs rise a bit then suddenly decide 1st gear should be engaged and bang it in. It's like you caught it unawares and then it has to quickly catch up with what you want. This doesn't happen every time though, it's always fine from a standstill and only ever does it if you are rolling forward and it's absolutely fine at speed.

The last time I had it on a Richards Lexia it said it couldn't find the gearbox ECU and gave up.

I do have the 4HP20 manual but it gives me a headache.

I've done the diode mod but it didn't make any difference and again, the Lexia didn't show any fault in that area, just the usual steering sensor etc. which Richard cleared for me. I will open the ecu up when I get time to see if there's anything suspect in there, then I'll get it reset.

Sid_the_Squid · Post by **Sid_the_Squid** » 29 Jun 2009, 19:47

Stempy my gearbox does the exact same thing, but again only sometimes too, approaching junctions or round-a-bouts is when its most noticeable. Its been a bit better on mine since the auto adapt re-initialise, however I'm not 100% sure the auto init road test was conducted at the correct time, so going to re-init again this weekend under more controlled circumstances. Will report an update then.

But from what I've been reading seems the 4HP20 gets 'confused' when crawling easily.

Stempy · Post by **Stempy** » 29 Jun 2009, 19:55

Have you updated the software on yours i.e. do you have the latest version?

Post by **CitroJim** » 29 Jun 2009, 20:06

Mine does the same thing so I guess if the three of us have much the same then it must be a "characteristic"

I don't put too much store in mine being 100% given it's provenence and "bitsa" construction. Mine has, after all, been cobbled up from the bits of two...

It'll be worth going into finding the reason why your ECU is of the strong, slient type Stempy. It's obviously working so I guess there is a problem on the wiring or diagnostic socket.

I've not checked my software version yet... I must do...

Sid_the_Squid · Post by **Sid_the_Squid** » 29 Jun 2009, 20:30

Did not know there was a software update to be had? Can your Lexia do that Jim?

Sid_the_Squid · Post by **Sid_the_Squid** » 29 Jun 2009, 20:32

I would have thought yours a good example Jim having a lot of new internal parts, probably less worn than mine after its 117k

Post by **CitroJim** » 29 Jun 2009, 23:48

Sid_the_Squid wrote:Did not know there was a software update to be had? Can your Lexia do that Jim?

Yes it can Sid. I'll have a look ready for a proper look on Saturday.

Sid_the_Squid · Post by **Sid_the_Squid** » 30 Jun 2009, 08:56

Post by **CitroJim** » 01 Jul 2009, 13:16

Last evening I put the Lexia on my V6 with the intention of updateing the autobox software. It appears the latest is Version 6 and the olny change from V5 on my gearbox is that in V6 the warmup map is modified so that the 'box does not hang on to 1st gear for so long during the 132.6 second 'box warm-up phase. This is where 2nd is not selected until the engine is revving at 3000rpm

This was apparantly done to make the engine and cat warm up fast in the guise of "depolloution"

I did try to update but after going through the motions, the Lexia informed me there was no CD in the drive and bottled out

I'm not sure which CD it wanted or even if I have it...

One thing I did though was to re-initialise the auto-adaptives and then immediately took the car out for the recommended long drive of variations.

I'm happy to report that after that little exercise it is noticely better and the 1st gear snatch is much reduced

Sid_the_Squid · Post by **Sid_the_Squid** » 01 Jul 2009, 13:57

Doesn’t sound like much of a reason to upgrade, even though the warmup mode annoys me each morning, sounds like a boy racer going down the road, its really no big deal, on the days I'm not rushing, letting idle for a min is usually enough to get normal operation. As an aside is there any indication when 6.0 firmware was made available? perhaps the mk2 Xantias have 6.0 already?

and then immediately took the car out for the recommended long drive of variations.

Jim is that ‘immediate’ as in auto adaption reset done, engine start, doors closed, off we go?

I'm happy to report that after that little exercise it is noticely better and the 1st gear snatch is much reduced

That’s the kind of result we like to hear