The Citroën XM was an executive car produced between 1989 and 2000.
The angular, dart-like Bertone design was a development of Gandini's Citroën BX concept. It was a longer car with a longer, inclined nose, more refined details and with headlamps that were very much slimmer than the norm.
The XM was reviewed by numerous automotive magazines during the course of its life. These reviews were generally favourable if inconsistent concerning particularly the car´s ride quality and appearance.
The hydropneumatic self-leveling suspension (featuring grapefruit-sized metal spheres containing nitrogen, acting as both springs and shock absorbers) gained a very sophisticated electronic control system called Hydractive, which used sensors in the steering, brakes, suspension, throttle pedal and transmission to feed information on the car's speed, acceleration, and road conditions to on-board computers. Where appropriate – and within milliseconds – these computers switched an extra suspension sphere in or out of circuit, to allow the car a smooth supple ride in normal circumstances, or greater roll resistance for better handling in corners.
The Hydractive system was somewhat "ahead of the curve" when the car was launched and early versions were sometimes unreliable. Many problems stemmed from the sensitive electronics controlling the car's hydraulic system, often caused by the poor quality of the multipoint grounding blocks — one on each front inner wing, one at the rear, and one under the dashboard. These tended to corrode (especially the ones in the engine compartment), causing all manner of intermittent faults which were hard to diagnose. On later cars, these were changed to screw terminals bolted through the bodywork, and most of the older cars have been modified in a similar way.
Source: Wikipedia, 2012