Citroën C4
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.
Punchy turbo compact
150 hp THP in the C4 I — noticeably more punch than the naturally aspirated, turbo-boosted pull from 1,400 rpm. Makes the C4 noticeably livelier; suffers from known THP problems.
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 6
The BSI (Body Systems Interface) on the C4 I is known for sporadic failures that lead to total failure of multiple vehicle systems. Moisture ingress into connectors promotes corrosion.
According to MOT statistics, brake discs on the C4 I wear above average, develop scoring and rust at the edges. MOT testers flag this frequently.
Driveshafts and axle joints on the C4 I are flagged above average by MOT testers. Steering joints and tie rod ends wear quickly, especially at higher mileages.
According to ADAC breakdown statistics, the C4 I is frequently flagged for flat batteries and failed starters. Permanent consumers in the standby current circuit can discharge the battery unnoticed.
According to MOT reports, the exhaust system on the C4 I rusts above average. Testers flag corroded exhaust pipes and clamps, which can lead to perforation and exhaust gas escape.
According to MOT statistics, headlights on the C4 I are one of the most frequently flagged items. Both low beam and tail lights are affected by failures and misadjustment.
