CITROEN C5 X7 trans ECU no connection

[bobby89bobby]

Hello good people from the French Car Forum.

I have a problem with my Citroën c5 X7

Bought the car as broken, had a melted piston.

2010 EP6DT engine with an Aisin 6 speed auto.

rebuilt the engine, the car started perfectly.
I drained all the trans fluid out when I took out the transmission, because I read that you can't drain it all out from the plug, you need to flush it etc and waste a lot of fluid.

The new fluid was ordered but delayed. I got the red amsoil signature series.

I ran the car to warm up twice without any oil for 10 15 min and then after I tipped it off with fluid and drove a small very gentle lap doing up to 30mph being enthused by the furst start and ride etc. no errors came up and it shifted fine.

Then it got a gearbox error and started to shift hard probably in limp mode. i cleared the errors using lexia diagbox. It returned to normal but only took 4 quarts of oil the first time. I didnt measure how much I drained out so I thought 3 were still in there since I read the trans has 7l in Total. after clearing the errors it took another quauartrr but no more.

Diagbox showed no communication with engine ECU, several modules had errors from no communication with engine ECU. The engine was running fine no check engine no fans going off except when warmed up at low speed. The BSI had unexpected reinitialization and no communication with passenger side mirror adjustment and seat memory module.

cleared them they did not go away and the right mirror is completely dead.

engine ecu communication was never established.

first test drive was behaving perfectly, babied it to 6th, went up to 50mph, did 4 5 miles, then I stoped and trying to park it it went into limp mode again, and first lost reverse. then reverse came back and it lost foreward drive. it was showing D3 the entire time.

I hooked up the lexia and erased the errors in the trans a couple of times. valve hi poped up a couple times and did not go away. I was in the middle of nowhere so I was a bit hasty.

suddenly it lost communication with the transmission. the laptop battery went down. I fiddled with the wiring and the fuses some nothing was out of order and I left it there. The car wouldn't turn over any more..i believe due the losing the trans ecu. the ABS module kept showing no communication with trans ecu.

The next day I went to fiddle with it some more and it was showing trans ecu, I cleared all the errors and it started. engine ecu still missing from diagbox.

I went to put in two more quarts of trans fluid as my mechanic friend had very modest experience with auto transmissions of the same type and he told me ot was probably low in fluid as the pump sends it up and fills.up.the torque converter hence you need to top it off on a working engine again and again till its actually full. Hr also reassured me no way could I damage the bkox from driving a bit low on oil.

anyway after putting in the fluid it wouldn't start again and diagbox shows no communication with the transmission and the abs ecu also shows no commm with trans error. wasn't able to bring it back and start it up.

when I was buying it I had some trouble with the people selling it. the car was parked at a mechanic shop who was a friend if the family the woman owner was blaming her husband who was driving it when it seized, I haggled the price down a bit and then the husband threw a fit and the price went up above the liated one. When i went to get it the subwoofer was removed and I was about to fight. It accidentally appeared somewhere from behind The shop. I found some more parts because I started to look around. I missed the cat and the second
o2 sensor but luckily I had one from another project. I wouldn't put it beyond that mechanic guy or the husband to have cut a wire ot two. they were arguing with me that it couldn't be repaired and asking me if I was a parts guy and wanted it to sell for parts.

Any ideas what this is and where I should start? I'm leaning towards a connection going bad at least for the lack of communication with the trans.

[wurlycorner]

It’s interesting that the engine runs, but you have no communication with the engine ECU - that is a surprise.
Tbh I would forget about the auto box for now and start there - re-establish comms with the engine ECU, because unless that is on the network, it will cause all sorts of other problems and if that’s been the consistent issue where the others are intermittent, then again, get the basics back to normal first.
You could try a BSI reset as the first simplest step, though I doubt that will fix everything in this scenario.
As you’ve also had the engine out, it is also worth doing a thorough and careful once around the engine bay checking for anything you may have forgotten to reconnect - especially a ground.
Then you really need the correct wiring diagram for the car, check all power and grounds are present at the engine ECU (it presumably must have some otherwise it wouldn’t be running at all, but it may be missing some) and check that they can actually carry current, not just continuity. If so, then a visual inspection of all wiring/pins/connectors at the ECU and check pin fitment etc.
If you can’t restore comms with it then, then it’s looking a little bit like it may be a fault with the ECU - especially if it does run, but won’t communicate.


Do you know what caused the melted piston originally?

[bobby89bobby]

The immediate cause was probably those two were having a fight and the husband was taking it out on the wife's car with a heavy foot.

There was oil soot everywhere, I don't know how often they changed the oil, even if they do the prescribed mileage and used Total, it's still what happens to these engines. In addition the cooling system was covered in lime scale. I used muriatic acid to clean it. The heater core for instance was plugged up. People have a tendency of using tap water to top.off and mix with coolant. Cars from Italy seem to especially have that problem. These engines are very sensitive to and easy to overheat, and lime scale is a killer for them.

None of that should matter now, everything is cleaned, the block resleaved, I'm using different pistons new mahle rings, lifters, head has new guides, lapped valves, new victor reinz valve seals, everything has been through ultrasonic cleaning. The engine runs like a clock. You can't hear it running when you're standing 10 feet away.

[Paul-R]

What version of Diagbox software are you using? Is the Diagbox hardware (Actia) full chip?

[bobby89bobby]

I've already done half a dozen of these engines in out rebuild and never had this happen. The only ground I have reconnected is the one for the engine itself that comes direct from the battery and goes on the gearbox. I'll check the grounds that go around the engine bay. I didn't think that taking it out someone might have disconnected any. Do you know where I can get a diagram? It would need to know how many I'm looking for and the general area.

I will get the ECU from my Peugeot, its from an ep6dts. It doesn't have the variable oil pressure for the pump but should be able to communicate with this car right? Just to see if it's able to get a reading on diagbox to eliminate the ECU itself as from being at fault.

I inspected the engine and trans ECUs' pins and it all seems fine, but you can't see into the plastic plugs' pins. I know they are easily breakable and you have to be careful not to switch pins around if you open them. I think I'll soak them in contact spray first to see if that helps.

Also I saw something perculiar; there is a fuse that is just hanging in the air by itself coming from a wire on the negative battery terminal. Another unfused wire comes from the positive and they both go into a cable lead and go into the big wire bunch connecting to the engine relay. I didn't follow it because I'd have to unwrap.the wire bunch, and it seems OEM, but at the same time that single.fuse does not look OEM it loks.like.something that they put in when installing an LPG system. I even asked if this car ever had lpg installed but they said no. I didn't see the fuse in any fuse diagrams for the car. It's just by itself hanging off the wire and is a large fuse, 10.amp, not a maxi but not the tiny one. The old school regular ones.

[bobby89bobby]

The diagbox version is 7.8 and it has always read my Peugeots from 2008 perfectly. Ep6dts and ep6.
The lexia is a clone but it should be a very good clone with full function. I spoke to the guy I got it from before this happened when I first saw the engine ECU having no comm, and he offered to double chech using his setup and he does this professionally he should be sure if it's my lexia or the car itself at fault.

[bobby89bobby]

I'll post of photo of the lexia unit and the diagbox window when I get some time to mess with the car.

[bobby89bobby]

Hello again. I finally got a chance to deal with the car.

Installed the ECU from my Peugeot. Diagbox can communicate with it. It's a version that the c5x7 does.not have, I think, and diagbox asked me to select it manually..there was no exact match with the list it have me, it had diesel ECUs', Med17.4 euro 5, but this is a med 17.4 euro 4. Anyway I selected the euro 5 and it reads it.

No communication with the gearbox still, won't let me start the engine, no apparent wires cut damaged unplugged, connected the cars original ECU, and again no communication.

[Paul-R]

What year is this X7?

[bobby89bobby]

2010

[bobby89bobby]

Update.
I reconfigured the bsi to have "missing" as the options for automatic transmission and presence of automatic transmission ECU.
The car now starts. I overrode the gear lever lock and it goes into gear and drives.

Puting it into drive and reverse is very jerky. It does not show gear info on the instrument cluster.
The engine is a bit rough and no info is shown for coolant and oil temps. The fan starts at max as if it has an error but unlike when it had an error does not persist when I shut the engine off. I have no idea what's going on since I can't access the engine ECU. Maybe because the bsi is not getting info about coolant temps it's macing out the fan.

I think I need a working engine and trans ECU to swap and see if they communicate.

I have a working engine ECU but as I've said that one is from my car and I need it. Maybe get a spare one and try to dump the CITROENs original ECU and reflash the spare one, basically clone it.

What do you guys think?

[wurlycorner]

That does sound like a sensible way forward now, yes. Though it's odd if they worked previously, why they've suddenly failed.
Unless of course, the car was delivered to you as a non-runner and you never ran diagbox before you'd replaced the Engine? In which case... This could be a fault that was there all along and you didn't know?!