C4 Grand Picasso 1.6 HDi MCP (CFC300P) - P0868 Pressure Drop Diagnostics & Test Data

[habo]

Hi all,

I am troubleshooting a hydraulic pressure issue on a 2006 Citroën C4 Grand Picasso 1.6 HDi fitted with the 6-speed MCP / EGS6 controlled manual gearbox (CFC300P ECU).

1. Fault Codes Logged (Diagbox)
CFC300P (Gearbox ECU): P0868 - Oil pressure defect fault (Local / Temporary / Characterisation: Pressure too low).

EDC16C3 (Engine ECU): P1394 - Gearbox ECU fault (Distant / Intermittent / Cruise control disabled by request of gearbox ECU).

2. Live Data Parameters (Engine Running, Idle)
Hydraulic Pressure: 34 Bar (Nominal operating range should be 40–50 Bar).

Status of Clutch: Slipping

Engine Speed: 800 rpm

Gearbox Input Speed: 241 rpm (in Neutral)

3. Pressure Leak & Load Test Results
Test A: Pressure Decay in Neutral (Engine OFF, Ignition ON)

Peak Pressure: 46 Bar

19:49 (+3m 15s): 41 Bar

19:50 (+2m 40s): 39 Bar

19:52 (+2m 10s): 37 Bar

(Gradual pressure drop over ~7.5 minutes without moving gear lever).

Test B: Gear Engagement Load Test (Engine OFF, Ignition ON)

Pump re-primed system to 46–47 Bar.

Selected Reverse (R) with brake pedal depressed.

Result: Hydraulic pressure dropped instantly from 47 Bar to 38 Bar.

Test C: Gear Engagement Load Test (Engine ON)

System at 42 Bar in Neutral.

Shifted into Reverse (R): Pressure dropped instantly to 38 Bar.

Shifted back to Neutral (N): Pressure climbed instantly back to 47 Bar.

4. Diagnostic Conclusion from AI (Gemini )
While the pressure accumulator ("sphere") on the electropump assembly appears worn due to the gradual pressure loss in Neutral, the instantaneous 8–9 Bar drop exclusively upon gear engagement (R) indicates a severe internal hydraulic leak in the Gear Selector / Actuator Unit (BVA HYD UNIT / Part 1), likely caused by failing solenoid O-rings or internal seal degradation in the clutch/gear actuator pistons.

Has anyone encountered this immediate pressure drop upon gear selection? Did replacing internal solenoid seals fix it, or did it require a complete overhaul/replacement of the hydraulic actuator block (BVA HYD UNIT)?

Thanks

[mickthemaverick]

I can't offer any comment but you may find something useful here: https://www.go-parts.com/garage/obd-p0868

[habo]

live data