The exhaust after-treatment is where modern diesels most often get expensive, especially in town driving. Here are its known problems for the checked diesel engines, with the mileage where they usually appear and a typical price.
Signs: DPF light, power loss or limp mode, oil level on the dipstick rising above max
Fix: Drive long enough at steady speed for regeneration or run a forced one, check the pressure sensor, change diluted oil early; clean or replace the DPF if it is blocked
Signs: Power loss, limp mode, EGR fault codes, rough running
Fix: Check the EGR valve in live data; clean it together with the throttle flap, replace the valve if it sticks
Signs: Sudden loss of power, engine light, fault code P2015
Fix: Check wiring and voltage, clean the manifold if the flaps stick, fit the modified actuator (Hyundai/Kia 28320-2A410)
Signs: Power loss, limp mode, EGR fault codes (e.g. P0401), black smoke
Fix: Check EGR position and flow in live data; clean or replace the valve, and the cooler if it is blocked
Signs: DPF light, frequent or interrupted regenerations, limp mode; worse with short trips
Fix: First check the differential pressure sensor and its hoses, then soot and ash load; forced regeneration, cleaning or replacement; use low-ash VW 507.00 oil
Signs: Engine light with P2015, reduced power, sometimes limp mode
Fix: Clean the manifold and fit a linkage repair kit, or replace the manifold with flaps; adapt the flaps with a diagnostic tool
Signs: Engine light, rough idle, hesitation, power loss or limp mode; worse with short trips
Fix: Check EGR movement in live data; clean or replace the valve
Signs: DPF light, interrupted or frequent regenerations, limp mode; mainly with short trips
Fix: Check and clean the pressure sensor hoses first, then read soot load; forced regeneration, cleaning or a new filter
Signs: Power loss, limp mode, EGR fault codes (P0401, P0403, P2413)
Fix: Check actual EGR flow in live data, clean or replace the valve; the cooler if it is blocked
Signs: Coolant loss with no visible leak, white smoke after a cold start
Fix: Pressure-test the cooling system and replace the EGR cooler before the cylinder head is damaged
Signs: DPF light, regeneration every few days, rising oil level (fuel in the oil)
Fix: Longer motorway drives; check soot and ash load and the pressure sensor; forced regeneration, cleaning or replacement
Signs: Power loss or limp mode, jerking, black smoke, EGR fault codes; mostly with city driving
Fix: Clean or replace the EGR valve; on older engines also check the vacuum solenoid and hoses
Signs: DPF warning, loss of power or limp mode, usually after mostly short trips
Fix: Forced regeneration with a diagnostic tool and a longer drive; check the pressure sensor and software; clean or replace the DPF if it is full
Signs: Jerking, black smoke, power loss or limp mode, EGR fault codes; mostly on cars used for short trips
Fix: Clean or replace the EGR valve; cleaning often helps only for a while
Signs: DPF or additive-level warning, limp mode after long periods of city driving
Fix: Refill the additive and reset the counter, check the pressure sensor, force a regeneration; clean or replace the DPF if it is full
Signs: AdBlue or emissions warning, countdown to no-start, engine light
Fix: Diagnose first: the pump is built into the tank and is replaced as one unit; crystals at the injector or the tank vent can sometimes be cleaned
Signs: Jerky idle, black smoke, power loss, EGR fault codes (e.g. P0401); worse with short town trips
Fix: Check EGR position in live data; clean the valve and intake, replace the valve if it sticks or its motor fails
Signs: DPF warning, frequent or interrupted regenerations, limp mode; mostly cars used for short trips
Fix: Check the differential pressure sensor and EGR first, then forced regeneration, cleaning or replacement; use low-ash RN0720 oil
Signs: Often none; coolant loss without a visible leak, white smoke or a burning smell
Fix: Have a BMW / MINI dealer check by VIN whether a recall is open; the EGR cooler or module is replaced free of charge
Signs: Power loss, rough idle, limp mode or EGR fault codes; worse with short city trips
Fix: Clean or replace the EGR valve and clean the intake
Signs: DPF warning, frequent or failed regenerations, power loss or limp mode
Fix: Check the differential pressure sensor first, then forced regeneration, cleaning or replacement
Signs: Coolant level keeps dropping, damp traces near the pump or EGR cooler, white smoke or EGR faults, temperature warning
Fix: Pressure-test the cooling system; replace the EGR cooler or the water pump (pump best together with the timing belt)
Signs: EGR fault codes, power loss, higher fuel use, more frequent regenerations
Fix: Check EGR operation in live data; clean or replace the valve
Signs: DPF light, frequent or incomplete regenerations, power loss, higher fuel use; mainly with short trips
Fix: Check the differential pressure sensor and hoses first; forced regeneration, cleaning or a new filter
Signs: AdBlue or emissions warning with enough fluid in the tank, countdown to no-start, codes such as P20E8, P21C5 or P20EE
Fix: Check the filler cap vent valve first (a new vented cap can cure it if caught early); otherwise the tank with built-in pump is replaced as one unit; also check the AdBlue injector for crystals and the NOx sensor
Signs: DPF or additive warning, frequent regenerations, power loss or limp mode after a lot of city driving
Fix: Refill the additive (about every 120,000 km) and reset the counter, check the pressure sensor and the additive pump, force a regeneration; clean or replace the DPF if it is full of ash
Signs: Coolant level drops with no visible leak, white smoke on start-up, sweet smell, EGR fault codes
Fix: Pressure-test the cooling system and replace the EGR cooler soon; check that no coolant reached the cylinders
Signs: Engine light, rough running, power loss; worse with town driving
Fix: Clean or replace the valve; it can soot up again within 20,000-30,000 km if driving stays short
Signs: DPF light, frequent regenerations, limp mode; oil level rising if regenerations are cut short
Fix: Check the exhaust temperature and pressure sensors, drive 15-20 minutes at speed or do a forced regeneration; clean or replace the filter only if that fails
Signs: Jerky acceleration, power loss, engine light with EGR codes; worse with short town trips
Fix: Check EGR position in live data; clean the valve and intake or replace the valve if it sticks
Signs: Smell of exhaust in the cabin or engine bay, ticking or hissing leak, sometimes coolant loss
Fix: Find the leak with the engine running; replace the cracked EGR cooler or pipe and check with the dealer by VIN for any campaign on the EGR pipe
Signs: DPF warning, frequent or interrupted regenerations, limp mode; mostly cars used for short trips
Fix: Check the differential pressure sensor and EGR first, then forced regeneration, cleaning or replacement; use low-ash RN0720 oil
Signs: Usually none; the NOx trap loses efficiency through sulphur build-up, sometimes poorer performance
Fix: Have a Renault dealer check by VIN that the free ECU reprogramming was done
Signs: Swirl flap fault codes, uneven running or power loss; a broken flap or screw can enter a cylinder and damage the valves, piston or turbo
Fix: Inspect the intake manifold from about 150,000 km; clean it or fit a new manifold with flaps
Signs: Often none; coolant loss without a visible leak, white smoke or a burning smell; in rare cases the plastic intake melts
Fix: Have a BMW dealer check by VIN whether the recall was done; the EGR cooler is replaced free of charge
Signs: Power loss, jerky part-load running, EGR fault codes (e.g. P0401), soot in the intake
Fix: Check EGR valve and bypass flap with vacuum hoses; clean or replace the valve, replace cracked hoses
Signs: DPF warning, frequent or failed regenerations, limp mode (e.g. P2002); worse with short trips
Fix: First check the differential pressure sensor, its hoses and the thermostat; then forced regeneration, cleaning (if ash is high but the core is intact) or replacement; use LL-04 oil
Signs: Slight to clear power loss, P0401 (low EGR flow), rough idle, black smoke; a cracked cooler loses coolant into the intake
Fix: Compare EGR target and actual position in live data; clean the valve thoroughly or replace it, and the cooler if it is blocked or leaks
Signs: DPF warning, frequent or interrupted regenerations, limp mode
Fix: Check the pressure sensor and soot load first and fix any EGR or injector fault; forced regeneration, cleaning or replacement; use MB 229.51 / 229.52 low-ash oil
Signs: Loss of power, poor throttle response, black smoke, EGR or air-mass fault codes
Fix: Check the EGR valve and the MAF sensor in live data; clean or replace the EGR valve, and clean the intake manifold if deposits are heavy
Signs: Engine light with P2015 and 'Engine system service required', weak pulling at low revs, sometimes limp mode
Fix: Check the joint between actuator and flap shaft; fit a new joint or swirl flap kit, cleaning the soot from the inlet ports if the flaps are coked
Signs: Hesitation, power loss, engine light with EGR codes, limp mode
Fix: Clean or replace the EGR valve and adapt it with a diagnostic tool; check the EGR cooler
Signs: DPF warning, frequent regenerations, power loss; oil level rising above max on short-trip cars
Fix: Check the differential pressure sensor, run a forced regeneration or clean / replace the DPF; change diluted oil at once
Signs: Power loss, jerky running, limp mode, EGR fault codes; falling coolant level points to the EGR cooler
Fix: Check EGR position in live data; clean or replace the valve; if coolant is lost, pressure-test and replace the EGR cooler
Signs: DPF warning, limp mode, frequent regenerations; oil level above max because fuel dilutes the oil; mostly short-trip cars
Fix: Check the differential pressure sensor and EGR, let regenerations finish on a longer drive or force one; change diluted oil early; clean or replace the DPF only if it is really full
Signs: No symptoms; exhaust cleaning was reduced at lower temperatures
Fix: Have an Opel dealer check by VIN that the mandatory software update was done (needed for registration in some countries)
Signs: AdBlue or emissions warning with a countdown in km; if ignored, the engine will not restart; NOx sensor codes, sometimes limp mode
Fix: Read the codes at once; check for Mercedes SCR software updates, then test and replace the faulty NOx sensor, pump / heater or dosing valve
Signs: DPF warning, frequent or interrupted regenerations, reduced power
Fix: Drive longer runs or run a forced regeneration; check the pressure sensor and EGR first; clean or replace the filter if ash-loaded; use MB 229.52 / 229.71 oil
Signs: Rough idle, power loss, EGR fault codes (P0400 range), regenerations do not finish
Fix: Check EGR position and flow in live data; clean or replace the valve, and the cooler if it is blocked or leaking
Signs: DPF warning, limp mode; oil level climbs above max (fuel in the oil), mostly with short trips
Fix: Check the differential pressure sensor and its wiring first; change diluted oil early with RN0720 oil; ask a dealer by VIN for open technical campaigns before replacing the filter
Signs: Power loss, limp mode, EGR fault codes
Fix: Check the EGR connector and wiring for corrosion, then clean or replace the valve
Signs: Power loss or limp mode, black smoke, rough running, EGR fault codes; worse with short trips
Fix: Clean or replace the EGR valve; cleaning usually helps only for a while
Signs: DPF or additive-level warning, limp mode after long periods of city driving
Fix: Refill the additive and reset the counter, check the pressure sensor, force a regeneration; clean or replace the DPF if it is full
Signs: Loss of power, black smoke, EGR fault codes, limp mode
Fix: Check EGR function in live data; clean or replace the valve, and check the cooler
Signs: Often none; coolant loss with no visible leak, white smoke, sweet smell or burning smell; in rare cases the plastic intake melts
Fix: Have a BMW or MINI dealer check by VIN whether the recall was done; the EGR cooler (and if needed the intake) is replaced free of charge
Signs: Coolant level keeps dropping without a puddle, white smoke; or power loss and EGR fault codes from a sooted valve
Fix: Pressure-test the cooling system and check EGR data; replace the EGR cooler or clean / replace the valve; check the intake for soot
Signs: DPF warning, frequent or failed regenerations, limp mode; mainly with short trips
Fix: First check the differential pressure sensor, its hoses and the thermostat; then forced regeneration, cleaning or replacement; use LL-04 oil
Signs: Engine light with a flap position fault (e.g. P2015), power loss or limp mode
Fix: Clean the manifold if the flaps are sound; otherwise replace the intake manifold or the flap actuator
Signs: Power loss, jerking, rough idle, EGR fault codes or limp mode; worse with short trips
Fix: Clean the EGR valve, cooler and passages; replace the valve or cooler if stuck or leaking
Signs: DPF warning, frequent or failed regenerations, limp mode
Fix: Check the pressure sensor and injectors first (worn injectors raise soot), then forced regeneration, cleaning or replacement
Signs: Swirl flap fault codes, rough running or power loss; a broken flap can enter a cylinder and damage the engine
Fix: Inspect and clean the intake manifold at high mileage; replace the manifold or flaps if they are sticking or loose
Signs: Often none; coolant loss without a visible leak, white smoke when accelerating or a burning smell
Fix: Have a BMW dealer check by VIN whether the recall was done; the EGR cooler is checked and replaced free of charge
Signs: Power loss, rough idle, smoke, EGR fault codes; worse with short trips
Fix: Clean or replace the EGR valve and clean the intake manifold
Signs: DPF warning, frequent or failed regenerations, limp mode
Fix: Check the differential pressure sensor first, then forced regeneration, cleaning or replacement
Signs: Engine light with EGR codes (e.g. P04D9), reduced power, uneven idle
Fix: Check that the manifold recall is done, then clean or replace the EGR valve and cooler
Signs: DPF warning, frequent regenerations, limp mode
Fix: Forced regeneration; if that fails, professional cleaning or a new DPF
Faults, intervals and prices are indicative and collected from public sources and owner experience; always rely on the service book and a qualified workshop. Test statistics: DVSA – Anonymised MOT tests and results, Open Government Licence v3.0. Dutch tests: RDW Open Data (CC0). Engine versions: EEA, monitoring of CO₂ emissions from new passenger cars (CC BY 4.0, DG CLIMA). Owner complaints: NHTSA ODI (public domain). Recalls: DVSA Vehicle Safety Branch Recalls Database, OGL v3.0. Brand and model names are trademarks of their owners and are used only to describe the vehicles. How we check the data →
Updated 29/10/2026