2011 Citroën C4 Grand Picasso 1.6 HDi – Robotised Gearbox Fault When Hot

[Rods74]

Hi everyone,
I’m hoping someone may have experienced this problem with my 2011 Citroën C4 Grand Picasso 1.6 HDi robotised/automated manual gearbox.
The problem:
The car drives and changes gear normally when cold.
Once the gearbox/car gets hot, the fault appears.
When the fault occurs, the gear display flashes between A1 and A2.
Sometimes it will select a forward gear, but when I try to pull away, the engine stalls.
When selecting reverse, it can engage very harshly and the engine can stall.
The problem only occurs when the system is hot.
If I switch the car off and allow it to cool down, everything works normally again.
Once cooled, it operates normally again without touching or replacing anything.
The fault code being recorded is P0925 – Gear Shift Reverse Actuator Circuit.
Parts already replaced:
Complete clutch
Clutch actuator/solenoid
Complete robotic transmission/actuator unit
Transmission ECU
Unfortunately, replacing the complete robotic unit and ECU made no difference to the problem.
Because the fault is temperature dependent, disappears completely when the car cools down, and seems to cause problems during clutch/gear engagement, I’m wondering whether this could be a temperature-related electrical fault, wiring/connector issue, power or earth supply problem, or another component involved in the gear selection/clutch control system.
Has anyone experienced P0925 with the A1/A2 display flashing, harsh reverse engagement and/or stalling when pulling away, particularly when the gearbox is hot?
Any advice or similar experiences would be greatly appreciated.
Thanks in advance!

[mickthemaverick]

You didn't mention whether you had replaced the gearbox oil? If not then that is the next step. Check if the old oil has any sogn of coolant contamination if the car is fitted with a coolant driven gearbox oil cooler. If it is then also after you have driven it and got the fault state switch off wait 5 minutes and then carefully remove the coolant cap and see if there is any pressure in the system.

[Paul-R]

How many miles has the vehicle done? Has it ever had the gearbox oil changed?

[BarneyRubble]

Also make sure you only use the correct Citroen approved spec gearbox oil, nothing else.

[Rods74]

Hi all, thanks for your replies. This is a semi automatic gearbox. But yes gearbox oil changed as well as the hydraulic fluid.

[RichardW]

It's in Russian, but you should be able to get the gist - there appears to be a gear position sensor on the front of the box. In this case, green crusties in the connector, but I imagine in your case the sensor might be going bad when it heats up. The fault appears to be just gear selection rather than anything to do with reverse (there is a but in this vid where he shows the fault description chart)