I needed to reinstall the Lexia/PP2000 recently on a computer. Just as a quick description, and also a note to self for later use :-), these are the steps required. Although there are many descriptions floating around on the net, not all deal with the same versions and setups, and some are really long videos, so here are the important steps as a concise reminder.
A sharp popping sound and the door window slides (or falls) down. Nice surprise but it does happen as our cars age. The window lifter mechanism uses galvanized steel Bowden cables and these tend to rust over time, especially if the climate is rainy and wet, or the door gets damp inside for any reason.
What to do now? First of all, don't press the switches in this case. Allowing the motor to rotate will eventually jam the cables now loose, allowing them to jump from their proper guiding channels. This can lead to more extensive damage than just the snapped cable.
Many of the ECUs in the XM can store and replay error codes when asked. Usually, they are read and cleared using the Lexia diagnostic system originally used by the dealer garages (copies of this system are available on the Net from Chinese vendors now).
With the possibility of LEDs everyhere, even in all the switches, the radio cannot be left out. The buttons have LED illumination orginally, as well as the red theft deterrent warning light but the display background is provided by tungsten bulbs. But even with the LEDs, they are of a yellowish-greenish tint and rather dim, as technology two decades ago allowed. Besides, if you have part of your illumination burnt out, you'll need to repair it, anyway. So, let's see how it can be done.
Circuit layouts already universally adopted in computers finally made their way into contemporary cars. Although their functioning might be frighteningly complex for people used to traditional circuits, they actually make the cabling very simple and the addition of component interactions possible in ways never experienced before.
Conventionally, cars used individual wires connecting the various elements—steadily increasing in number—on board. The huge amount of wires, connectors, wiring harnesses were a constant source of connection problems. The various circuits were largely independent (sharing only the feed and the ground), although some components had to interact (for instance, fog lights should work only when the headlights are switched on), necessitating connections between the various components (usually using some kind of a switching logic, relays for simpler tasks and small electronic modules for more complicated ones).
As various subsystems (engine management, suspension, ABS, etc.) came from different manufacturers, some functions were even built in parallel. Several subsystems might rely on the signal sent by a coolant temperature or a vehicle speed sensor but it was simpler for the manufacturers to fit two or three such sensors into various places, using every one of them only by their respective subsystem, than to find ways to share the sensors, introducing interconnecting wires and the danger of one failing subsystem to influence the others.
The multiplex wiring first seen on late XMs and later used on newer models like the Xsara Picasso or the C5 introduces a radically different concept: just like in the computer used to read this book, there is a central backbone circuit called bus which goes around the whole car—actually, there are four of them, a Controller Area Network (CAN) and three Vehicle Area Networks (VANs), dealing with different areas: the CAN is only responsible for the connection between the central unit and the engine, gearbox and suspension computers, the VANs for the rest of the systems: the first serves the safety systems like the airbag, the second the various doors (including the sunroof) and the anti-theft system, the third everything else: the instrumentation and the comfort gadgets.
A rather simple, basic multimeter is enough to check and troubleshoot the electrical parts of the car. Such multimeters can be purchased at hardware or electronics stores. The picture shows a genuine noname multimeter although I saw the very same unit under many brand names and disguises. Noname meters may not be safe if used to measure higher voltages but in the 12 V network of the car there are hardly other risks than blowing some fuses.
Models with higher performance level came fitted with ABS.
The principle of operation is the same as on cars with conventional braking systems but the layout is much simpler as all we need to control the operating pressure of the brakes are a few electro-valves.
The brake compensator valve is the most complicated part of the hydropneumatic suspension. This component is not only responsible for the operation of the brakes but forms a central part of the whole system.
Another gem of engineering, the DIRAVI steering, made its debut on the SM, excelled in many CXs and the flagship, V6 XMs (left hand only, the small amount sold in the UK never justified the expenses of the conversion to RHD).
The DIRAVI (Direction Rappel Asservi, Steering with Limiting Counterforce) steering is as unique as the hydropneumatic suspension—it was never used by any other manufacturer, although its excellence over conventional power assisted systems speaks for itself.
As usual, it has some quirks confusing the average driver during their first meeting. First of all, it is geared very high: it only took two turns of the steering wheel from lock to lock (one turn for each side) to steer on the SM. Later models, the CX and the XM retained this feature although the number of turns was larger (2.5 and 3.3). The gear ratio could have been much higher, the engineers themselves insisted on a single turn lock to lock for the SM (which would, interestingly, void the need for a circular steering wheel completely). The final solution was a compromise to reduce the initial strangeness of the steering for the drivers already accustomed to traditional systems.
Certainly, making the gearing so high is not a complicated feat in itself but a conventional (even power assisted) system with such rapid a response would be unusable. As the car obviously has to have a similar turning circle as other cars, too responsive a steering would mean that even the slightest movement of the steering wheel would induce excessive deviation of the car from the straight line. To avoid this, it uses an opposing force, increasing with the vehicle speed. With this setup, in spite of the very high gearing, it is very easy to use it during parking, yet it offers exceptional stability at high speeds: it actually runs like a train on its rails, requiring a sensible amount of force on the steering wheel to deviate it from the straight line. And an additional feature: the steering wheel (and the roadwheels, naturally) center themselves even if the car is stationary.
The PAS steering (DIRASS, Direction Assistée) used on Citroëns is not radically different from similar systems on other cars. Naturally, having a high pressure hydraulic system at disposal influences the layout.
The fluid requirements of the various hydraulics subsystems differ significantly: while the brakes require only a very little amount of LHM and the suspension somewhat more, the power steering cannot work without large amounts of mineral fluid provided at a moment’s notice. A flow distributor built into the first hydraulic circuit—that of the hydraulic pump, the main accumulator and the pressure regulator—controls the hydraulic pressure between the steering circuit and the suspension-brake circuits on PAS cars.
The rest is rather simple. A hydraulic ram cylinder is mounted on the rack of a traditional rack-and-pinion steering gear unit. The pressure of the hydraulic fluid supplied to assist the driver in turning the steering wheel is controlled by the flow distributor and a control valve. The flow distributor has the following components: