V6 Xantia......... the beginning of another adventure

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Trainman
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Re: V6 Xantia......... the beginning of another adventure

Post by Trainman »

Ok, Jim found a 'broken' wire' between the engine ECU and the Gearbox ECU causing the engine speed sensor to give a high resistance reading.

The cable feed both the rev counter and gearbox ECU from a splice, I knew the rev counter was fine, so that left the from the splice to the gearbox ECU, this was tested and an independent wire has been run between the two.

The original ECU has been returned to the car, and he's been road tested, with the gearbox going up and down as it should.

The leak off pipes have been replaced with the new ones I collected on Tuesday, so the only thing left is the cruise control.......

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CitroJim
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Re: V6 Xantia......... the beginning of another adventure

Post by CitroJim »

The way the gearbox ECU gets the engine speed signal is intertesting. It's not directly from the speed sensor but a buffered signal from the engine ECU which is also used to drive the tacho. We found the resistance between the Engine ECU speed output and the gearbox ECU speed input was very high when measured between ECU connectors. On the Lexia the speed signal on live data was seen to be all over the place and more often than not zero. It was the same but less pronounced on the ELIT.

We compared with my V6 and saw a solid, steady signal.

Tellingly the signal passes via the infamous 10AV loom which runs under the rad. More tellingly the speed signal passes through a splice which we suspect is the cause of all our heartache. The splice is more or les inaccessible unless the bumper and wing is removed so we did the next best thing and installed a bypass wire between ECU connectors.

Tested on the Lexia and ELIT the Gearbox ECU is now seeing a solid speed signal. It definitely wasn't before.

Had a nasty moment when I thought I'd blown up the spare ECU when it went for a download but thankfully after a battery off it came good. Simon, it has version 5 software, Does then mean anything?

So, hopefully it's now fixed. At least we found something very tangible and definite.

Now to fix the cruise contriol to round off the day...

Trainman
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Re: V6 Xantia......... the beginning of another adventure

Post by Trainman »

The cruise control, is hopefully just dirty contacts on the brake pedal switch, Jim has cleaned these, and checked the switch is functioning, which it appears to be. I will perform the road test tomorrow on the way home.

I can't thank Jim enough for sorting this out, hopefully this work today has solved the problems (crosses fingers) and I can put this to bed, once and for all.....

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Re: V6 Xantia......... the beginning of another adventure

Post by KP »

Fingers and toes crossed for you fella :)

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Mandrake
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Re: V6 Xantia......... the beginning of another adventure

Post by Mandrake »

Nice work Jim! =D>

The wiring between the two ECU's was always high up on my suspect list, (and it's the only likely thing that really fit the symptoms 100%) but suspecting it as a cause and physically tracking down the fault and proving it conclusively is something else. :) From Jim's description Steve I'm pretty confident the fault has finally been found and fixed. 8-)

So now that you've seen this wiring fault Jim, do you think this problem may be more common than we realise, given the splice and the fact that it runs through the infamous radiator cable bundle ? How high was the resistance reading you were seeing ?

Interesting that most of the time the gearbox seemed "OK" before dropping into emergency mode, but I wonder how much of an effect on the smooth operation of the torque converter lockup clutch a marginal/intermittent signal might have ?

Comparing the engine speed signal (which was faulty in this case) with the gearbox input speed sensor (which is actually after the torque converter but before the simpson gears) is the way in which the ECU monitors the torque converter slip and makes adjustment to the torque converter clutch pressure to regulate the slip precisely.

If that engine speed signal was intermittent and all over the place it stands to reason that the torque converter clutch would not be controlled properly. It wouldn't affect the gear changes because gear change thresholds are based on the road speed (differential) sensor signal not input or engine speed, but it would affect control of the torque converter clutch I'm sure.

Now that you've found this problem I'm intensely curious as to whether the "problem child" had a problem with this signal, because it was always the torque converter lockup control that was problematic on that car, there is a possibility that the root cause was an electrical problem... #-o

For the symptoms Steve was getting its likely the connection was going completely open circuit (or almost so) at the moment the fault was logged and it dropped to emergency mode, but a less drastic failure of just a high resistance joint could have been causing trouble on the other car. I guess I'll never know now... :?

As soon as I have somewhere other than the side of the road to work I'll be taking the battery tray out of the new V6 and carefully measuring the resistance of that wire between the two ECU's!

So let me check, was the wire between pin 43 of the engine ECU and pin 40 of the gearbox ECU ? I only have the S2 wiring diagrams so hopefully this part is the same as the S1 - if not would you be able to post the relevant diagrams for the wiring between the two ECU's at some point ? :)

Did you also check the two other wires that go between the two ECU's ? (One being engine load, the other torque reduction control) If they're going through the same wire bundle they might also be prone to failing the same way, and the engine load signal could cause the gearbox not to kick down properly - a problem that the problem child also had sometimes... :roll:

As for software version Jim - the actual "version" number is not the one that changes when you update, it's always 5. It's the "Edition" number that changes, the old firmware is edition 0501, I don't recall what the new firmware edition is but its a slightly higher number. :lol: Also I believe the "number" field - which is normally 1, is the number of times it has been programmed. 1 = programmed once at the factory, 2 means it has been programmed a second time etc...

Here is a screenshot from my new V6:

Image

KP
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Re: V6 Xantia......... the beginning of another adventure

Post by KP »

Are you thinking this is something that would help the gearbox on your old one Simon? I only ask as the only thing I can pickup from it is he random misfire below 4k revs. It's fine a lot do the time and generally poottling along but sometimes when you want full lift off from the lights you can feel it almost big down and then when it hits there it's fine all the way upto the top of the speedo where private road conditions allow :D

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Re: V6 Xantia......... the beginning of another adventure

Post by KP »

Oxymoron alert...

French Electrician :D

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CitroJim
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Re: V6 Xantia......... the beginning of another adventure

Post by CitroJim »

Mandrake wrote: So now that you've seen this wiring fault Jim, do you think this problem may be more common than we realise, given the splice and the fact that it runs through the infamous radiator cable bundle ? How high was the resistance reading you were seeing ?
On my sensitive multimenter the resistance between ECUs varied between 5 and 20 ohms but that was misleading as the meter uses a tiny current for resistance measurement. When the meter was set to audible continuity - which takes more current - it measured a solid open-circuit.
Interesting that most of the time the gearbox seemed "OK" before dropping into emergency mode, but I wonder how much of an effect on the smooth operation of the torque converter lockup clutch a marginal/intermittent signal might have ?
I've been thinking exactly the same Simon!
Comparing the engine speed signal (which was faulty in this case) with the gearbox input speed sensor (which is actually after the torque converter but before the simpson gears) is the way in which the ECU monitors the torque converter slip and makes adjustment to the torque converter clutch pressure to regulate the slip precisely.
Yes, absolutely. It had to be affecting this aspect of gearbox operation.
Now that you've found this problem I'm intensely curious as to whether the "problem child" had a problem with this signal, because it was always the torque converter lockup control that was problematic on that car, there is a possibility that the root cause was an electrical problem... #-o

For the symptoms Steve was getting its likely the connection was going completely open circuit (or almost so) at the moment the fault was logged and it dropped to emergency mode, but a less drastic failure of just a high resistance joint could have been causing trouble on the other car. I guess I'll never know now... :?
Will might find out but I don't believe this was the problem Simon as it would have surely logged a fault at some point or dropped into third emergency...
So let me check, was the wire between pin 43 of the engine ECU and pin 40 of the gearbox ECU ? I only have the S2 wiring diagrams so hopefully this part is the same as the S1 - if not would you be able to post the relevant diagrams for the wiring between the two ECU's at some point ? :)
Yes, precisely. S1 and S2 are identical in this area.
Did you also check the two other wires that go between the two ECU's ? (One being engine load, the other torque reduction control) If they're going through the same wire bundle they might also be prone to failing the same way, and the engine load signal could cause the gearbox not to kick down properly - a problem that the problem child also had sometimes... :roll:
No, because they're not spliced Simon, only the speed signal has a splice, all the others are direct.

Thanks for the information on software versions Simon :-D

It's been an interseting day. :-D I'm switching off for the evening now. Not surprisingly I'm just a little tired :lol:

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Re: V6 Xantia......... the beginning of another adventure

Post by Hell Razor5543 »

Sleep well Jim. A job well done. I hope that is the end if it.

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Re: V6 Xantia......... the beginning of another adventure

Post by Trainman »

Hell Razor5543 wrote:Sleep well Jim. A job well done. I hope that is the end if it.
It is and I think we all do, it's been a pain in the derriere over the last year. Jim and I were talking before and it seems this issue has been going on for a good 5 to 10 years, apparently Roger Bradford asked Jim to look at it sometime ago, but passed away before Jim could, hopefully Roger has looked over us today and we've had a spot of divine intervention

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daviemck2006
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Re: V6 Xantia......... the beginning of another adventure

Post by daviemck2006 »

I hope there's no more problems with it Steve and it turns into the great car you want it to be. Lucky guy with 3 v6 cars to choose from and all of them getting diesel economy :mrgreen:

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Re: V6 Xantia......... the beginning of another adventure

Post by Trainman »

Xantia and Peugeot should actually get better, and that really pleases me

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Re: V6 Xantia......... the beginning of another adventure

Post by BW »

Hoping that the problem is solved, it is a really nice car and they are getting rarer all the time. Years of fun for you Steve.
I can just about understand what's been happening but am in awe of those who can diagnose and deal with these things.

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Re: V6 Xantia......... the beginning of another adventure

Post by Trainman »

Bill, I saw Jim reading those diagrams today, it was like trying to understand a knitting pattern....

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Re: V6 Xantia......... the beginning of another adventure

Post by KP »

The hardest thing in the V6 is speed! Keeping it at legal levels is a challenge that is all consuming whilst driving as I can safely say of I took mine over to Germany I could quite happily set the cruise at 130-max and not worry about it. The frequent fuel stops would annoy me but hey ho!

To be honest Steve if the xantia was fine for another month and all sorted now I wouldn't convert the 407.

Id sell it and be happy with the two you have left but maybe swap the C6 for a petrol one with all the toys and then have economy and the C6 for special occasions with a conversion fitted :)