Citroën C6 (2005–2012): history, engineering and weak spots

The Citroën C6 was meant to replace the XM and show that Citroën could build a saloon unlike its German rivals. It reached the market five years later than planned, sold poorly and left the range after seven years. In this piece I have gathered the model's history, its key engineering and the weak spots described in British buying guides. For the context of other French cars of the period, see the piece on French youngtimers.

Where did the Citroën C6 come from?

The C6 grew out of the C6 Lignage concept, shown at the Geneva Motor Show in spring 1999. It was to replace the XM, whose production ended in June 2000, and Citroën hoped to launch it by the end of 2000. According to Wikipedia, the car only went on sale in November 2005, five years behind schedule.

The production version was shown in Geneva in March 2005, and sales began on 16 November 2005. The design was the work of Marc Pinson. The car was built at the PSA plant in Rennes. It is 4,907 mm long, with a 2,901 mm wheelbase, and weighs 1,818–1,871 kg.

The C6 quickly became the car of French presidents. According to French Wikipedia, Jacques Chirac was driven in a black C6 as early as 14 July 2005, before the market launch, and Nicolas Sarkozy, François Hollande and Emmanuel Macron later used C6s too.

How many were built, and why so few?

By 19 December 2012, 23,384 cars had been built. Production peaked in the first full year of sales and then fell quickly:

Source: Wikipedia (based on PSA reports). Right-hand-drive cars were built until May 2012.

There were several reasons. Prices in France started at €39,400 for the base version, and the Exclusive started at €49,650. Autocar wrote in 2018 that the C6 never caught on with the Audi and BMW drivers it was aimed at, while the most expensive versions cost about £40,000 in the UK and depreciated very quickly.

A note for anyone searching: the Citroën C6 sold in China from 2016 is an entirely different car that shares only its name with the European model.

How does Hydractive 3+ suspension work?

Hydractive 3+ is the final generation of Citroën's hydropneumatic suspension: each wheel has its own damper and gas spring unit, with pressure controlled by a computer. Unlike older Citroëns, the system does not balance pressure between the corners of the car but regulates each one individually (Parkers).

The key features of the system:

• LDS fluid: orange and synthetic, instead of the green mineral LHM of older Citroëns. The two must not be mixed up.
• Seven spheres filled with nitrogen. According to Autocar, even a slight drop in gas pressure noticeably changes how the car sits.
• Three automatic modes: motorway, poor road surface, and either comfort or dynamic.
• Adjustable ride height: the driver can raise or lower the car.

The result is a very soft ride. Parkers notes that on the motorway you may feel slight diagonal body movement, but the car should isolate you from small imperfections.

Which engines and gearboxes did the Citroën C6 have?

The C6 had four engines: two V6 diesels, a four-cylinder diesel and a petrol V6. According to French Wikipedia:

The gearboxes were a six-speed Aisin AWTF-80 SC automatic and a six-speed manual, dropped by October 2008. Autocar says most surviving cars are 2.7 HDi automatics, while the 2.2 HDi sold poorly. The petrol V6 is rare today. When the 3.0 HDi replaced the 2.7 in 2009, only the top Exclusive trim remained in the UK.

What made the C6 stand out from its rivals?

The C6 had several features unusual for a 2005 saloon. The active bonnet and the deploying spoiler were reserved for the V6 versions.

• Active bonnet: in a collision with a pedestrian it rises by 65 mm using a pyrotechnic charge, increasing clearance above the engine.
• Deploying spoiler: it rises in two stages, at about 65 and 125 km/h, to improve stability when braking from high speed.
• Euro NCAP: five stars in 2006 and the first car to earn four stars in the pedestrian protection test.
• Head-up display (HUD), lane departure warning, directional xenon headlamps and nine airbags.
• Frameless double-glazed side windows, which drop slightly when the door opens.

What are the Citroën C6's weak spots?

The most expensive problems involve the V6 HDi engine, the Hydractive 3+ suspension, the automatic gearbox and the electrics. Below are the points from the Parkers (2024) and Autocar (2018) guides.

V6 HDi engine

The V6 HDi is mounted transversely, so access to the timing belt, fuel pump, EGR valves and turbochargers is restricted. Parkers warns that the V6 HDi is particularly prone to oil dilution, which can end in serious failure. At a viewing, smell the dipstick: a whiff of diesel is a bad sign.

• The DPF uses Eolys additive, topped up during servicing. DPF problems are common on low-mileage cars.
• Juddering that feels like a misfire can point to EGR valves or injectors.
• Leaks around the turbochargers and intercooler pipework.
• Bodges: Parkers lists bypassed EGRs, hollowed-out DPFs and wiring to fool the ECUs. Ask about them directly and check during the diagnostic scan.
• Cooling system: according to Autocar, the plastic thermostat housing cracks and the steel coolant pipe in the left front wheelarch can rust through.

Suspension

A hard ride and thumping over speed bumps usually mean a worn sphere. A soft ride at high speed or uneven behaviour in Sport mode point instead to an electrical fault or a sticking valve. Parkers suggests checking that the headlights turn with the steering, which indirectly tests the steering angle sensor. A complete strut with fitting can cost over £1,000. Autocar also mentioned regassing the spheres (about £320 in 2018) and corroded suspension pipes.

The front suspension comes from the Peugeot 607 and 407 Coupé, but according to Parkers it was not strengthened for the C6's near two-tonne weight. Bushes and balljoints wear quickly, leading to uneven tyre wear and knocks.

Automatic gearbox

The main threat is the gearbox oil cooler, which is part of the engine's cooling circuit. When it fails, gearbox oil mixes with the coolant. Shudders or jolts between gears are a warning sign. According to Autocar, a careful owner changes the gearbox oil every 20,000 miles, despite the manufacturer's "sealed for life" claim. A slow response when pulling away, on the other hand, is normal.

Electrics and body

• The battery is in the boot. Parkers recommends at least 100 Ah and 950 CCA for the V6, because a weaker battery causes ECU faults.
• Instruments: check that every segment of the display works.
• Door locks and the drop mechanism of the frameless windows.
• Galvanic corrosion: according to Autocar, where the aluminium bonnet and doors meet steel.
• Spoiler: it should rise in two stages.

Which C6 should you choose, and how do you check it?

The choice usually comes down to the 2.7 V6 HDi, because there are most of them. Parkers describes the 3.0 V6 HDi (240 PS) as very rare, more powerful and arguably more reliable. In 2018 Autocar noted a 2010 3.0 HDi with 12,000 miles selling for £24,000, while ordinary 2.7s started at about £2,250. The petrol V6 is, according to a specialist quoted by Autocar, the quietest but also rare.

Before buying, take a test drive on the motorway and in town, read the fault codes with a diagnostic tool that supports PSA systems, raise and lower the suspension several times, and check the fluids: LDS (light orange) and engine oil (no smell of fuel). Parkers also suggests contacting a Citroën club, where it is easier to find someone who knows the model.

The C6 succeeded the XM, which in turn replaced the CX. An example of the latter, a 1985 Citroën CX 25 GTi Turbo, is in the MB Classics archive. Other French cars worth a look are in the list of 7 French future classics. Current cars for sale are on the MB Classics stock page, and more guides are on the MB Classics blog.