Peugeot 508 2.0 HDi Mk1

The pre-facelift 508 HDi uses an additive-assisted DPF system with Eolys cerine fluid stored in a separate tank. This additive lowers the soot ignition temperature to help the filter regenerate. Short trips under 15-20 minutes prevent the exhaust from reaching regeneration temperature, gradually blocking the filter. Symptoms include the anti-pollution warning, engine warning light, and reduced power. A professional forced regeneration with diagnostic tools costs 150-250 euros. Chemical DPF cleaning runs 300-500 euros. Full DPF replacement costs 800-1,500 euros depending on OEM or aftermarket parts. The Eolys additive tank needs topping up approximately every 120,000 km at around 100-150 euros. A key warning sign before purchase: if the engine oil level is well above the maximum mark and smells of diesel, this indicates chronic regeneration failure and fuel dilution of the oil. Cars with regular motorway use rarely develop this problem.

The 508 Mk1 has a complex rear suspension with an H-shaped subframe mounted to the chassis via four large rubber bushings. These bushings deteriorate from road salt, vibration, and age, typically starting around 60,000-80,000 km. Symptoms include clunking or knocking over bumps, vague rear-end handling, and uneven inner rear tyre wear. Each bushing costs approximately 70-150 euros for the part (around 145 GBP per set of two). Total repair including wheel alignment runs 400-800 euros at an independent specialist, as the subframe must be partially lowered for access. This issue often needs addressing more than once during a 10-year ownership period. Inspect the bushings visually from underneath for cracking and separation before purchase.

The electronic parking brake on the 508 Mk1 is a widely reported weak point. Water can seep into the EPB motor unit via the emergency release cable access hole, corroding internal components. Symptoms include a 'Parking brake fault' message on the dashboard, the brake failing to release on start-up, or intermittent engagement. Before committing to expensive repairs, check the 12V battery voltage: many owners have found that low voltage (below 11.8V) triggers false EPB warnings that resolve with a fresh battery. Also check the 20-amp EPB fuse, as a blown fuse is another common cause. The EPB switch itself costs 50-100 euros. Caliper motor replacement runs approximately 300-500 euros per side. Full EPB module replacement costs 500-600 euros. Diagnosis requires Peugeot-specific software (Diagbox/Lexia) as generic OBD tools often cannot communicate with the EPB system.

The EGR valve on the DW10 engine accumulates carbon deposits from recirculated exhaust gases, particularly on gently driven cars and those used mainly for urban journeys. Mechanics familiar with the 508 note that while all diesel EGR valves eventually foul, the 2.0 HDi is more robust than the smaller 1.6 HDi in this regard. Symptoms include rough idle, flat spots during light acceleration, and increased fuel consumption. Cleaning with the valve removed costs 150-250 euros and can restore normal operation for 6-12 months. A new EGR valve with fitting costs 300-600 euros at an independent workshop. The valve is located at the rear of the engine, making access awkward and adding to labour time. Regular motorway driving and quality diesel help reduce carbon accumulation.

The 2.0 HDi produces 340-400 Nm of torque, which gradually fatigues the dual mass flywheel over time. Symptoms include metallic rattling at idle that changes when the clutch pedal is pressed, and juddering when moving off in first gear. Typical failure occurs between 130,000-180,000 km depending on driving style. The DMF should always be replaced together with the clutch assembly (and slave cylinder), as gearbox removal is required for access. Scheduled labour time is approximately 6 hours. An independent garage charges 800-1,200 euros for parts and labour using quality aftermarket components (such as Valeo or LUK kits). A Peugeot dealer quotes 1,200-1,600 euros with OEM parts. Urban stop-start driving and riding the clutch accelerate wear. Solid flywheel conversion kits exist as an alternative but may increase gearbox vibration.

The variable-geometry turbocharger uses an electronic actuator to control vane position. Carbon deposits from the EGR system gradually restrict actuator movement, particularly on gently driven cars that rarely reach higher RPMs. Symptoms include intermittent limp mode, engine management warnings, and noticeable power loss. If caught early, specialist actuator repair costs 200-400 euros. If the internal turbo vanes are also seized or bearings are damaged from insufficient oil supply, a complete turbo replacement is needed at 1,200-2,000 euros fitted. The DW10 2.0 HDi turbo is more durable than the smaller 1.6 HDi unit, with failures typically not appearing before 150,000 km. Always replace the oil feed line when fitting a new turbo to prevent recurrence from oil coking.

A well-documented issue on the 508 Mk1 where the central display powers up briefly then goes black after a few minutes, or fails to start at all. Radio and Bluetooth may continue working while the screen remains dark, making navigation and climate controls inaccessible. The pre-facelift models use the SMEG or eMyWay system. The root cause is typically a failing internal component in the head unit. Specialist electronics repair services offer head unit rebuilds for 200-300 euros. A new or refurbished replacement unit from Peugeot costs 400-600 euros including dealer coding. Used units from breakers are available for 100-200 euros but also require coding. While frustrating, this issue does not affect vehicle drivability.

If the 508 is equipped with the 6-speed Aisin AM6 automatic (also known as TF-80SC, used in Volvo, Jaguar, and other PSA models), the valve body electro-valves can fail over time. Symptoms include harsh or delayed gear changes, jerky shifts in stop-start traffic, and the gearbox entering emergency mode. Hard shifts can worsen when coolant temperature exceeds 90 degrees. Valve body replacement at a Peugeot dealer costs 1,800-2,500 euros. A transmission specialist can repair or replace the valve body for 800-1,500 euros. Regular ATF changes (recommended every 60,000 km despite the claimed lifetime fill) help prevent this issue. Manual gearbox variants do not have this problem.