Citroën DS4
The EP6DT/EP6CDT (Prince THP) is the most problematic engine from the PSA-BMW cooperation. Timing chain wear, high oil consumption, and VVT solenoid failures occurred on a large scale; camshaft sprocket slipping was only resolved from 2012 with harder gears. Short oil change intervals (max. 10,000 km) and quality 5W-30 engine oils are mandatory.
Sprightly Picasso
With 150 hp THP the small C3 Picasso becomes surprisingly quick. Turbo punch and compact dimensions make it agile in city traffic.
Engine Weaknesses 7
The THP engine suffered severely from timing chain stretch caused by the weak single-row tensioner, combined with camshaft sprockets slipping on the shaft. This leads to uncontrolled valve timing loss and can cause piston-to-valve contact. PSA improved the sprockets from model year 2012 onwards.
Symptoms: Rattle on start-up, power loss, rough idle, check engine light P0011/P0012, in the worst case engine damage without warning
THP engines frequently consume 1–3 litres of oil per 1,000 km from around 80,000 km, in extreme cases up to 4 l/1,000 km. Causes are worn exhaust valve stem seals and piston rings worn from soot deposits.
Symptoms: Very frequent oil top-ups, blue or white smoke from exhaust, black deposits on spark plugs, oil smell in engine bay
The THP turbocharger suffers from insufficient oil supply, especially when the oil level drops too low or the oil degrades from excessively long change intervals. Oil coke from the crankcase also blocks the oil feed line to the turbo.
Symptoms: Whistling or rattling turbo noise, blue smoke under full load, power drop, measurable boost pressure loss
The high-pressure fuel pump (HPFP) on the EP6 THP fails frequently and results in insufficient fuel rail pressure. The engine stumbles on cold start or under load. Part number 1920LL (THP 150) or 1920RT (THP 200).
Symptoms: Stumbling on cold start, fault code P0087 fuel pressure too low, power loss under full load, hesitant throttle response on acceleration
In the EP6 THP, a secondary chain drives the oil pump. This secondary chain wears and can break. The result is a drastic drop in oil pressure that causes immediate engine damage if the STOP warning is ignored.
Symptoms: Oil pressure warning light (STOP), pressure drop despite correct oil level, metallic noises, in the worst case engine shutdown
Direct injection without intake valve wash, combined with EGR recirculation, promotes soot deposits on the intake valves. In PHEV use with frequent electric driving, cold start condensation can make the problem worse.
Symptoms: Rough idle, starting difficulties when cold, engine stumbling, power loss
The wastegate control system on the EP6 THP is vacuum-operated with inverted logic. The solenoid valve for the vacuum supply fails frequently, leaving the wastegate open and preventing any boost pressure from building.
Symptoms: Vehicle only accelerates weakly as if naturally aspirated, maximum speed limited to 100–110 km/h, no turbo boost felt, fault code P0299
Vehicle Weaknesses 4
The electric power steering in the DS4 I can fail — the steering servo motor gives up, making the steering extremely heavy. Causes are typically ECU faults or defective connectors at the column motor.
The central BSI control unit in the DS4 I is prone to software faults that simultaneously trigger warning lights for ABS, ESP, ASR and the parking brake. The cause is often moisture in connectors or a weak 12V battery.
Corrosion at the ABS sensor wheel bearing seats causes the sensors to seize and become impossible to remove. The underfloor can also rust broadly on neglected vehicles.
Brake discs on the DS4 I wear above average, especially in urban use. Surface rust after extended standstill causes loud squealing on the first braking application. Front discs are more severely affected.
