BMW 420d G22

All BMW B47 diesels are susceptible to EGR problems. The valve clogs with carbon deposits, causing hesitation, increased fuel consumption, and check engine codes. More seriously, the EGR cooler can leak glycol coolant internally, which when mixed with soot and high exhaust temperatures can ignite. BMW issued a major recall (approximately 800,000 vehicles worldwide) covering B47 diesel engines for EGR cooler replacement. An updated cooler from a different supplier has been used since 2022. EGR valve replacement alone costs around €200-500 at an independent shop. If the intake manifold is damaged from a cooler leak, costs can reach €1,500-2,500 including manifold replacement. At approximately 100,000 km, walnut blasting the intake system is advisable to remove carbon buildup. Always verify the EGR cooler recall has been completed before purchase.

The DPF needs regular driving at motorway speeds (30+ minutes above 80 km/h) to complete passive regeneration. Cars used primarily for trips under 15 km accumulate soot faster than it can burn off, eventually triggering a DPF warning light and power reduction. Forced regeneration at a workshop costs €150-400. Professional chemical cleaning runs €400-800. If the DPF is beyond cleaning, replacement costs €2,500-3,500 at a BMW dealer. Before buying, use BMW diagnostics (ISTA or BimmerLink) to read the DPF soot and ash loading values. A car showing high soot levels has likely been used for predominantly short journeys. Prevention is straightforward: regular motorway runs at sustained speeds.

This is a well-documented issue across the G20/G22 platform. Service technicians report seeing multiple cars per week with this problem. Moisture penetrates the mirror housing and causes a short circuit in the electronics module. It typically starts with one mirror failing, then the other follows months later. In some cases the door master controller is also affected, disabling window controls and the trunk release. Under warranty, BMW replaces the mirrors free of charge. Out of warranty, independent mirror specialists charge €300-500 per mirror. BMW has updated the mirror seal design on later production cars. Check both mirrors fold and unfold smoothly during inspection.

The B47 diesel uses an SCR (selective catalytic reduction) system with AdBlue injection to meet Euro 6 emissions standards. NOx sensors upstream and downstream of the SCR catalyst can degrade, producing fault codes like P2200 and P20EE. Symptoms include a threatening countdown warning on the dashboard stating the engine will not restart after a certain number of kilometres. A single NOx sensor replacement costs €350-700 at a dealer. The complete AdBlue pump and tank assembly, if it also needs replacing, can reach €1,200-2,000. The G22's newer ECU hardware makes independent diagnosis more complex than on older F-series cars. Using only BMW-approved AdBlue and keeping the tank above a quarter full helps prevent crystallisation issues.

The ZF 8-speed transmission's oil cooler can fail internally, allowing engine coolant and automatic transmission fluid to mix. This is a serious failure: coolant contamination in the gearbox causes harsh shifting, slipping, and eventually transmission damage if not caught early. Symptoms include unusual fluid leaks, a burning smell, and the transmission warning light. The repair requires replacing the cooler and thermostat, flushing both the cooling and transmission systems. At an independent specialist, parts and labor typically run €800-1,500. If transmission damage has already occurred, costs at a BMW dealer can reach €2,500-3,000. ZF recommends transmission fluid changes around 100,000 km despite BMW's 'lifetime fill' claim — ignoring this accelerates wear.

The valve cover gasket on the B47 engine is made of rubber that hardens and loses its seal over time due to repeated heating and cooling cycles. Oil seepage typically becomes visible at 60,000-100,000 km, appearing as oil stains near the top of the engine. If left unaddressed, leaking oil can drip onto hot exhaust components and create a burning smell inside the cabin. The repair involves removing the valve cover and replacing the gasket. Independent shops charge €350-500; BMW dealers typically quote €500-700. This is a straightforward repair and rarely leads to further complications when addressed promptly.

The G22 420d uses a 48V mild hybrid system with a belt-driven integrated starter-generator (ISG). While generally reliable, failures of the ISG can block the entire 48V electrical network, discharge both the lithium-ion 48V battery and the 12V battery, and leave the car unable to start. Replacement of the ISG unit is expensive due to the part cost and integration with the engine's ancillary belt drive. The 12V battery in mild hybrid BMWs also tends to discharge more readily because the alternator only charges during deceleration. Keeping the car on a trickle charger during extended periods of non-use is recommended. This issue remains uncommon on the G22 but worth monitoring as the cars age.