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• The hydraulic suspension pump (Citroën calls it the “Electro-Hydraulic Power Unit” or “BHI – Built-in Hydroelectronic Interface”) is the heart of the Hydractive III / III+ system fitted to all Citroën C5 HDi models (2001-2017).
• It is an electric motor-driven high-pressure pump that draws LDS fluid from the reservoir, raises it to ≈150–180 bar, and feeds a valve block that sets vehicle height and damping.
• Typical faults are worn motor brushes, blown maxi-fuse (40–50 A), seized relay, internal leaks, or fluid contamination.
• Diagnosis is best done with Lexia/Diagbox, checking live pressure (15–17 MPa desired) and BHI fault codes; electrical checks and a visual leak inspection follow.
• Repair options: replace brushes or complete pump, fit re-manufactured BHI, flush and refill with genuine LDS only, then bleed the system with the diagnostic tool.
System architecture
• C5 Mk I (2001-2004): separate pump and ECU, external valve block.
• C5 Phase II (2005-2008): more compact assembly, ECU clipped to pump.
• C5 X7 (2008-2017): fully integrated BHI (pump + ECU + valve manifold) – part nos. 9642295680, 9654068680, 4701 P1/P2 (suffix varies by year).
Hydraulic circuit essentials
• LDS reservoir → low-pressure hose → gear-type pump → check valve → accumulator/gallery (150–180 bar) → electro-valves → suspension struts + steering.
• Pressure sensor feedback to ECU; pump runs only until target pressure is reached.
| Failure modes & symptoms Fault category |
Typical DTC / symptom | Root causes |
|---|---|---|
| No start/“Serious suspension fault” | BHI faults C1141, C1167 | Blown maxi-fuse FL4 (40/50 A), seized motor, open-circuit relay, corroded connector. |
| Continuous running, overheats | DTC C1140, pump on >30 s | Internal leak in valve block, leaking sphere membrane, stuck pressure regulator, relay contacts welded. |
| Slow/weak lift, car sinks overnight | Low pressure reading <10 MPa | Worn pump gears, cavitation due to low fluid, clogged internal filter, worn brushes. |
| Noise (whine/grind) | Audible on height change | Air ingestion, depleted LDS, bearing failure, cavitation damage. |
Diagnostic workflow
a) Visual/level check – LDS must be orange-clear, level midway between MIN-MAX with suspension on “normal”.
b) Electrical: verify 12 V supply at pump connector while commanding height change; check relay (usually in front right wheel arch) and maxi-fuse blade adjacent to under-bonnet fuse box.
c) Scan with Lexia/Diagbox: read pressure (15–17 MPa), run actuator test, log DTCs.
d) Mechanical; if pressure <14 MPa and current draw normal (<45 A), pump section worn; if current >60 A or fuse blows, motor short/seized.
e) Optional hydraulic gauge inline to confirm pressure specification (workshop procedure).
| Repair / replacement decisions Option |
Pros | Cons |
|---|---|---|
| Brush & bearing replacement (~€30) | Cheap, DIY possible, keeps OEM core | Requires soldering, dismantling crimped can, only cures motor faults. |
| Re-manufactured BHI (e.g., eBay PN 9654068680) | Bench-tested, warranty, mid-price (€350–550) | Core exchange, still need bleed/calibration. |
| New OEM (PSA PN 4701P1-P4) | Full spec, latest revision, long life | €950–1200, scarce for early Mk I. |
| Used unit (breakers, ProxyParts) | Cheapest (€100–200) | Unknown history, spheres often flat, limited life. |
Installation highlights
• Depressurise: With Lexia “depressurise circuit” or manually slacken 6 mm bleed screw one quarter-turn (wear eye protection).
• Cap/label four rigid pipes (M10 ×1 and M12 ×1 threads) to prevent contamination.
• After fitment: fill with fresh LDS, perform “hydraulic circuit priming” routine, then calibrate ride-height sensors (front/rear potentiometers).
• Typical bleed sequence: raise to “high”, lower to “service low”, repeat twice; finish at “normal”.
• Parts availability: dismantlers list >180 C5 pumps on ProxyParts.com, typical savings 40–60 % versus new.
• Rebuild services: European specialists (e.g., ECU-Testing, Actronics) offer BHI overhaul with upgraded brushes and MOSFET drivers.
• Industry shift: Citroën discontinued hydropneumatics after 2017; current “Progressive Hydraulic Cushions” in C5 X are passive, so C5 HDi owners increasingly rely on the remanufacturing market.
• Brush retrofit kits (graphite 6 × 4 × 12 mm) and 3-D-printed brush holders are now sold online to extend pump life at low cost.
• Why LDS only? LDS is a synthetic ISO 46 fluid with very low aeration and elastic-seal compatibility. LHM (green) swells the orange LDS seals and will destroy the BHI.
• Accumulator sphere: acts as a pulse damper; when its nitrogen bladder depletes (<20 bar pre-charge) pump cycles more often, accelerating wear.
• Electrical load analogy: the pump is similar to a 500 W DC motor; voltage drop through corroded connectors can starve it, just as a dim light bulb indicates high resistance.
• Pressure safety: the circuit stores up to 180 bar; accidental loosening of a rigid pipe can inject fluid under skin—always depressurise.
• Fluid disposal: LDS is classed as hazardous waste; dispose via licensed recycling centres.
• Warranty: fitting non-type-approved fluids or used pumps can void insurance in some EU countries—document repairs.
• Preventive: change LDS every 5 years/80 000 km; clean reservoir gauze filter; check spheres at 60 000 km.
• Carry 1 L of LDS in boot for emergency top-ups.
• If pump is noisy on cold mornings, test battery: <11 V cranking can stall the motor and blow the maxi-fuse.
• After any height sensor replacement, recalibrate ride height in ECU to avoid uneven tyre wear.
• Some early Mk I cars share fluid with DIRAVI-style power steering; most HDi variants keep steering separate—consult VIN-specific parts diagram.
• Brush replacement fixes ≈60 % of dead pumps; hydraulic gear wear or cracked housings are non-repairable in‐car.
• Always use new ‘olive’ seals on rigid LDS pipes; re-using them is the top cause of weeping joints post-repair.
• Investigate solid-state relay retrofit to eliminate contact welding.
• Explore synthetic LDS substitutes meeting PSA S71-2710 spec (research ongoing).
• Monitor community forums (FrenchCarForum, Citroen-Owners-Club) for emerging BHI ECU firmware updates that improve pressure control.
• Academic angle: model cavitation damage in small-gear pumps running LDS vs. mineral oil for improved design.
The Citroën C5 HDi’s electro-hydraulic pump pressurises LDS fluid to control Hydractive suspension height and damping. Failures usually stem from worn brushes, electrical supply faults, or fluid contamination. Systematic diagnosis with Lexia, electrical tests, and pressure measurement pinpoints the fault. Repairs range from inexpensive brush replacement to full BHI exchange; always refill with LDS and bleed/calibrate afterwards. With regular fluid changes, leak checks, and sphere maintenance, pump life can exceed 250 000 km despite the discontinuation of new hydropneumatic models.
