The 2021 Peugeot 508 is a stylish midsize sedan with a mixed reliability record — the gasoline PureTech engines suffer from timing belt failures, the diesels face EGR/DPF headaches, and the PHEV hybrid shows electrical gremlins. Build quality is decent, but engine longevity depends heavily on proper maintenance intervals.
PureTech 1.6L Wet Timing Belt Failure
Common · high severityTypical onset: 60,000-100,000 mi
Symptoms: Metallic rattling from engine bay on cold starts, Oil contamination with white/gray sludge in filler cap, Check engine light with timing correlation codes, Catastrophic engine failure if belt disintegrates
Fix: The timing belt runs in oil and deteriorates prematurely, shedding material that clogs oil passages. Full engine teardown required — timing belt, water pump, oil pump, complete flush, often valve damage. 12-18 hours labor if caught early, full rebuild (40-60 hours) if belt fragments cause piston/valve collision.
Estimated cost: $3,500-12,000
BlueHDi Diesel EGR Valve and Intake Manifold Carbon Clogging
Common · medium severityTypical onset: 50,000-90,000 mi
Symptoms: Loss of power especially under load, Black smoke from exhaust on acceleration, Rough idle and hesitation, P0401 or P0403 EGR flow codes
Fix: EGR valve sticks, intake manifold fills with carbon deposits. Requires EGR valve replacement, intake manifold removal for walnut blasting or replacement, new gaskets. 6-8 hours labor. Short trips accelerate buildup dramatically.
Estimated cost: $1,200-2,200
PHEV Hybrid System Battery and Charging Faults
Occasional · high severityTypical onset: 40,000-80,000 mi
Symptoms: Hybrid system warning light with reduced power mode, Failure to charge or hold charge, Erratic transitions between electric and gas modes, 12V auxiliary battery drain issues
Fix: High-voltage battery cell imbalance or cooling system failures, onboard charger module defects, hybrid control module software issues. Diagnosis requires factory scan tools (3-4 hours). Battery module replacement 8-10 hours, charger module 4-5 hours. Many require dealer-level programming.
Estimated cost: $2,500-8,500
Transmission Oil Cooler Leaks (EAT8 Automatic)
Occasional · medium severityTypical onset: 70,000-110,000 mi
Symptoms: Transmission fluid puddles under vehicle, Delayed or harsh shifting when cold, Burnt smell from transmission area, Low fluid level on dipstick check
Fix: External oil cooler lines and cooler seals deteriorate. Requires cooler assembly replacement, new lines, complete fluid flush. 4-6 hours labor. Catching early prevents transmission damage from low fluid.
Estimated cost: $900-1,600
Head Gasket Failure (1.5L BlueHDi)
Occasional · high severityTypical onset: 80,000-130,000 mi
Symptoms: White smoke from exhaust persistently, Coolant loss without visible leaks, Overheating or erratic temperature gauge, Milky oil on dipstick or under oil cap
Fix: Head gasket fails between cylinders or into coolant passages. Cylinder head removal, resurface or replacement if warped (common), new gasket set, timing belt while open, coolant flush. 14-18 hours labor. Head resurfacing adds 2-3 days turnaround.
Estimated cost: $2,800-4,500
Diesel Particulate Filter (DPF) Clogging and Regeneration Failures
Common · medium severityTypical onset: 45,000-85,000 mi
Symptoms: DPF warning light illuminated, Limp mode activation with power loss, Increased fuel consumption, Failed regeneration cycles
Fix: Short trips prevent passive regeneration, soot clogs DPF. Forced regeneration via scan tool (1 hour) if caught early, otherwise DPF removal for cleaning ($600-800) or replacement. Includes differential pressure sensor replacement often. 3-5 hours labor for filter swap.
Estimated cost: $800-2,800
Pass unless it's a well-documented low-mileage example with full service history — the PureTech timing belt is a ticking time bomb, and diesel emissions gear is maintenance-intensive.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.