C4 Grand Picasso Stalling after EGS replacement U0304

[justinzak]

Hi there,
My names justin and I'm a part time auto sparky. I have come across an EGS problem which I could not find online, which I thought would be productive for me and the community to solve here.

I have a customer with a C4 Grand Picasso (facelift) with the EGS/ASMT transmission which was struggling with all gear changes.
It had been turned away from a dozen mechanics, including citroen dealers who seemingly 'forgot' to make bookings.
The diagnosis was that the actuator assembly was buggered and needed swapping completely.

The customer came to me with a complete EGS assembly which he wanted swapping and programming.
I reluctantly agreed and after some struggles, it is installed, holds pressure and shifts through all the gears first time.

A problem has arisen since the replacement - a fault code on the engine computer "U0304" - incompatibility in communication with the gearbox.
The car stalls regulary when coming to a stop and sometimes, stalls after firing up. After looking up the fault code - the symptoms seem to align with what we are seeing. Stalling, hesitation, difficulty starting etc.
As a result, I can complete the stationary learning tests with the Lexia, however am unable to complete the dynamic driving learning tests - due to stalling out on each stop.



When the vehicle stalls, it is a little bit like a sticky egr valve type of stalling - if i had to describe a similar situation.
The fault code suggests checking CAN lines and Engine ECU, however I know connectivity is good as the same CAN lines connect the ABS and/or EPB (cant remember which)
I was wondering if perhaps, the cause is due to software differences between a facelift DV6C and non facelift DV6xx software variant on the EGS ECU?
As his vehicle is a july 2011, and the donor is a 2009 - one could be programmed to talk to a Bosch EDC16 and the other programmed to talk to a Continental SID807?
I cannot find any programming/service functions for swapping the ECU other than copying the counters over and doing the gearbox learning.

My next step might be to transplant the EGS ECU between the two actuator assemblies to rule out software issues, but thought I'd check in with this forum first and hopefully contribute this scenario to the already vast set of problems on this forum.

Thank you very much!

[GiveMeABreak]

All I can tell you is that there are several ECUs for these boxes and the correct one is obviously important for everything to work.

To confirm this I would need to have the VIN for the current vehicle and the donor vehicle to check if the part numbers are the same - unless you still have the labels on the ECUs of both - but I guess if you did, you would already know that they would be different.

(please post your VINs in full without spaces - it will be automatically masked from public view after submitting your post & will only be visible to staff).

[justinzak]

Thank you for the response, I don't doubt that there are several part numbers and successions to this ecu. I usually don't expect the same part numbers as they seem to get superseded every few months.

The vin of this car is VF7**************[VIN obfuscated, can be read by forum staff]
We don't have the vin of the donor car.

I will get both part numbers off the ECUs tonight and report back

Kind regards

[GiveMeABreak]

That's correct, but even the replacement part numbers for the ECU units are specific to the exact engine type and gearbox variants.

Let me have the other info when you get it, but ideally the VIN would of nailed it.

[justinzak]

Its no wonder we can't contact the owner of the donor vehicle - looks like it is from an 07.
I'd usually put this research in myself but In this scenario I've simply walked in and been asked to swap a part and take no ownership/liability
Original part;
MM_BVMP_MCP_CEM1
9674693580
Donor part;
MM_BVMP_MCP_CEM0 (I think the CEM1 and the CEM0 are the big red flags here)
9664965580

Hardware looks identical - I'm guessing its simply different software loaded onto the mcu/eeprom?

[GiveMeABreak]

As I thought, those are the international part numbers and not PSA numbers, so all I can say is yes, as you have surmised, the key is the part 96* number which must match the original unit.

[justinzak]

Turns out the circuit board is super easy to swap over. It was apparent that both boards had different componentry. Once the boards were swapped, the fault codes cleared and everything was perfect again. Hopefully this helps whoever wants to swap actuator assemblies from different vehicle configurations