Although every aspect of the functioning of the Hydractive systems was described in the previous chapters, considering the number or factors influencing the suspension and the amount of rules and decisions made by the computer, it is not easy to grasp the actual behavior of the car, including the differences in the various Hydractive generations. To make it easier, we summarize how the various Hydractive systems work in real life.
The new C5 has a new suspension system, doing away with many solutions used on Citroëns for several decades, yet offering the same or even better comfort than before. Recent developments in electronics and computics made it possible to delegate many functions previously solved by mechanical-hydraulical components to electronic units.
This third generation suspension system retains the same basic functioning as the previous systems. It also comes in two flavors: a simpler Hydractive 3 reminiscent of the original hydropneumatic suspension of the DS–GS–BX–CX and a slightly more complicated Hydractive 3+, building upon the former Hydractive I and II (actually, Hydractive 3 is not hydractive in the sense we used this term before, its only special activity is to adjust the road clearance depending on speed and road condition).
Although the basic functioning is practically the same, the actual layout underwent significant changes. Most importantly, the previously mechanically operated height correctors became electronically controlled hydraulic units. And all hydraulic units except for the spheres—which were redesigned to give unlimited life expectancy—are now housed in a single unit, the Built-in Hydroelectronic Interface (BHI). This compact unit has three main parts:
The second incarnation of the hydractive suspension appeared at February 1, 1993 (ORGA 5929). It was designed to overcome the biggest problem of the previous system, the very uncomfortable hard mode.
Switching to Sport does not mean sticking to a hard, uncomfortable ride any more. On the Hydractive II, the relation between suspension modes and dashboard switch settings became more complicated: in both settings—Normal (the new name of Comfort) and Sport—the computer can switch to both hard and soft mode as it finds it necessary, however, when set to Sport, the suspension becomes more sensitive and will sooner and more often switch to the hard mode.
Many models were also fitted with an anti-sink system that locks the system when the car is not running, using yet another sphere. Its only purpose is to keep the car from sinking when not used, it does not influence the functioning of the suspension system in any way.
The Hydractive I suspension system appeared with the XM. Unlike the simpler hydropneumatic suspension used on the DS, GS/GSA, CX, BX and some XMs, this one has two modes of operation, soft and hard. The suspension functions in soft mode but it will be switched to the hard mode when the computer deems this necessary for the sake of roadholding and safety.
To achieve this, the first hydractive system adds two spheres (one for each axle) and an electric valve to the struts and spheres of the standard hydropneumatic setup.
During normal driving, the computer keeps the suspension in soft mode most of the time but—based on the input provided by many sensors (steering wheel, accelerator pedal, body movement, road speed and brake), including the Sport/Comfort switch on the dashboard—the suspension ECU decides when to switch to hard mode; in other words, when to deactivate the additional spheres for extra roadholding and safety.
When the driver selects the Sport setting, the suspension is switched to hard mode constantly. This setting is not what any Citroën driver would call comfortable… The successor system, Hydractive II overcomes this limitation.
The ECU operates three electrovalves to switch the suspension between hard (default) and soft modes. There are three parts involved in this operation:
Follow the instructions in the Comments column.
Noise from the front
There are several possible causes. The connecting rod ball joints might be worn (there are two of them for each rod, they connect the strut to the anti-roll bar). There are two types of rods, adjustable and fixed length; the replacement rods will usually be fixed. If you find an adjustable one on your car, replace both of them.
The steering rod ball joints might be worn.
Failures in the Hydractive system (generally problems with sensors or their wiring) can force the suspension to be stuck in hard mode. To diagnose the fault, it would be convenient to know which mode the car is currently in. As H II systems use a 1 kHz chopper to form the current operating the valves, this leads to an interesting way to learn the current status of the suspension: this chopped current actually disturbs the radio reception. Tune your radio to a spot somewhere near 700 kHz where there is no incoming broadcast.