The second-generation 4 Series coupe slots the proven B48 2.0-litre turbo four into BMW's CLAR platform, producing 258 PS, with the 245 PS 430i xDrive arriving in July 2021 and the facelift following in March 2024. BMW applies 48V assistance to the six-cylinder engines and the four-cylinder diesel rather than to this four-cylinder petrol. Paired with the ZF 8HP automatic and available in RWD or xDrive, it shares nearly everything with the G20 3 Series mechanically. The B48 has a strong track record at this point, with front-mounted timing chain and a robust bottom end, though plastic cooling components and oil sealing remain the main ownership themes.· more· less
Plastic housing cracks or gasket degrades, causing oil or coolant leaks onto engine components · more· less
The B48 oil filter housing is made of plastic and sealed with a rubber gasket that deteriorates from heat cycling. Typically between 80,000 and 130,000 km, the gasket fails or the housing itself cracks. In the worst scenario, coolant mixes with engine oil internally, visible as milky residue on the oil cap or dipstick. This can cause bearing damage if not caught quickly. BMW has faced a class-action lawsuit over this component across B46, B48, and B58 engines. Gasket-only replacement at an independent shop costs approximately €400-600. If the housing itself is cracked, the complete unit including labour runs €600-1,200. Many specialists recommend upgrading to an aftermarket aluminium housing to prevent recurrence.
Coolant vent line cracking
up to €4002 of 7
Small plastic hose between cylinder head and expansion tank becomes brittle and snaps · more· less
A rigid plastic coolant vent line connects the cylinder head to the expansion tank. Positioned near the turbocharger, it is exposed to significant heat cycling and becomes brittle over time. The line has been redesigned at least three times by BMW. When it fails, coolant is lost rapidly, and the engine can overheat if not stopped promptly. Symptoms include a sweet smell from the engine bay and white residue on the engine top. The BMW service action usually quoted for this line, SIB 17 01 21, covers F22 and F3x cars built up to September 2019 rather than the G22, so do not assume free replacement. Ask a BMW dealer whether any campaign applies to this VIN. If not covered, independent repair runs €150-400 including parts and labour.
Water pump and thermostat failure
up to €1,2003 of 7
Coolant pump or thermostat housing fails, typically between 80,000 and 120,000 km · more· less
The B48TU's main coolant pump is belt-driven from the engine rather than electric, and its plastic impeller is prone to cracking; the thermostat housing can also develop leaks. Most technicians recommend replacing both together due to the shared location, which reduces total labour. Symptoms include low coolant warnings, erratic temperature readings, or poor cabin heating. At an independent shop, expect €500-800 for both water pump and thermostat including labour. BMW dealers typically charge €800-1,200. This is a proactive maintenance item that many specialists recommend addressing between 80,000 and 120,000 km rather than waiting for failure.
Valve cover gasket and PCV system failure
up to €1,0004 of 7
Integrated PCV diaphragm tears or gasket seeps, requiring full valve cover replacement · more· less
The B48 integrates its PCV (positive crankcase ventilation) system into the plastic valve cover. When the PCV diaphragm tears or the valve cover gasket seeps, the entire assembly typically needs replacing because BMW does not sell the PCV valve separately. Symptoms include a whistling noise at idle, increased oil consumption, and visible oil seepage around the cover edges. This typically develops between 100,000 and 150,000 km. The valve cover assembly costs approximately €200-350 for parts. Labour runs 3-4 hours due to the need to remove fuel injectors and multiple electrical connections. Independent shop total: €500-700. BMW dealer: €700-1,000.
Charge pipe failure
up to €6005 of 7
Plastic turbo charge pipe cracks under boost pressure, causing sudden power loss · more· less
BMW uses a rigid plastic tube to route pressurised air from the turbo to the intercooler. Under hard acceleration the plastic can crack or burst at the throttle body flange, resulting in a loud pop, total loss of boost, and a drivetrain malfunction warning. This is more common on tuned cars but does occur on stock cars as well, typically above 60,000 km. The OEM replacement is plastic again. Many specialists recommend upgrading to an aluminium charge pipe kit from aftermarket suppliers, which costs €150-300 for parts and eliminates the issue permanently. Including labour, expect €200-400 at an independent shop or €400-600 at a BMW dealer.
Starter relay corrosion and fire risk
€0 (recall)6 of 7
Starter relay corrodes and can short-circuit, posing a fire risk even when parked · more· less
Two different starter actions are usually run together and should not be. One concerns metal abrasion deposits in starter relays retrofitted between July 2020 and July 2022, which is a fitment window rather than a production window. The separate water ingress and corrosion action covers about 1.145 million vehicles worldwide, where moisture reaching the relay can cause corrosion, overheating and in rare cases a short circuit and fire; that is the one BMW attached a park-outside advisory to. A further July 2026 campaign, KBA 16790R, covers more than 740,000 vehicles worldwide including 4 Series cars built from 31 July 2020 to 26 February 2026. The remedy is free starter motor replacement at any BMW dealer. Verify completion with any BMW dealer using the VIN before purchasing.
iDrive software glitches
up to €2507 of 7
Screen freezes, spontaneous reboots, and smartphone connectivity issues reported widely · more· less
Launch G22s run Operating System 7; iDrive 8 with the Curved Display became standard from March 2023. Both have been reported by many owners to suffer from occasional screen freezes, spontaneous reboots, and Bluetooth or CarPlay connectivity drops. These are software issues that BMW addresses through over-the-air or dealer-performed updates. Most are resolved without cost if the car is kept on the latest software version. In rare cases, the head unit hardware itself fails and needs replacement, which can cost €200-250 at an independent shop for parts and programming. While not a mechanical reliability concern, the frequency of reports makes it worth noting.
Well-understood engine, but plastic cooling components need monitoring
The B48 is one of BMW's more reliable modern engines and many examples exceed 200,000 km without major powertrain issues. The main ownership theme is plastic cooling and oil system components that degrade with heat cycling. Proactive replacement of the coolant vent line, water pump, and oil filter housing gasket between 80,000 and 130,000 km prevents the costliest scenarios. The ZF 8HP automatic is robust when serviced with fluid changes every 60,000-80,000 km. Use the VIN to establish which of the starter campaigns applies and that the work was done; KBA 16790R alone covers 4 Series cars built from 31 July 2020 to 26 February 2026.
Service history
Complete BMW dealer or specialist records essential. Verify oil changes at 15,000 km intervals or shorter, not BMW's maximum 30,000 km recommendation.
Tires
Check tread depth, age (date codes), and uneven wear patterns. Run-flat tires are standard and expensive to replace.
Cold start
Start the engine completely cold. Listen for unusual rattles or knocking in the first 30 seconds.
Test drive
Minimum 30 minutes including highway speeds. Check for smooth shifts and confirm no drivetrain malfunction warnings appear.
Specific for this vehicle
Inspect oil filter housing area for leaks
Look under the intake manifold for oil residue or coolant traces. Check the oil cap and dipstick for milky residue indicating coolant contamination.
Check coolant level and expansion tank
Low coolant suggests a leak in the vent line, water pump, or oil filter housing. Look for white crystalline residue on top of the engine near the turbo.
Verify starter motor recall completed (VIN decides the scope)
Several separate starter campaigns exist with different scopes, including KBA 16790R for cars built 31 July 2020 to 26 February 2026. Contact any BMW dealer with the VIN to confirm recall completion.
+ 3 more checksShow less
Test the iDrive system thoroughly
Navigate through menus, connect your phone via Bluetooth and Apple CarPlay/Android Auto. Watch for screen freezes or reboots during the test drive.
Listen for whistling at idle
A whistling or squealing noise from the engine at idle can indicate PCV diaphragm failure in the valve cover. This requires full valve cover assembly replacement.
Check for charge pipe integrity under hard acceleration
During the test drive, apply full throttle briefly. A sudden loss of power with a pop sound indicates a cracked charge pipe.
Recalls and Technical Service Bulletins
Starter relay water ingress and corrosion, fire risk even when parked - worldwide action covering about 1.145 million vehiclesCritical - verify completed
Starter relay metal abrasion deposits - relays retrofitted between July 2020 and July 2022Critical - verify completed
Starter campaign KBA 16790R (July 2026) - more than 740,000 vehicles worldwide, 4 Series built 31 July 2020 to 26 February 2026, VIN confirmation requiredCritical - verify completed
ECU incorrect programming affecting automatic door locking (2022-2023 models serviced at dealer)Verify if applicable
The starter campaigns are the most significant safety concern on this car, and BMW attached a park-outside advisory to the water ingress action until the work is done. There are several of them with different scopes and different date windows, so contact any BMW dealer with the VIN rather than reasoning from the model year.
Warranty Status
Factory warranty (market-specific, 2 to 3 years)Expired on 2020-2022 models. 2023+ may still be covered.
Rust perforation warranty (12 years)Active on all G22 models (production from 2020)
BMW Extended WarrantyAvailable through BMW dealers, typically €1,000-1,500/year
BMW warranty terms are market-specific rather than Europe-wide: Germany runs a 2+1 programme, the UK gives three years, and BMW France states two years. Early 2021 models are now outside warranty. The 12-year rust perforation warranty remains active on all G22 cars. Extended warranty is available but check exclusions for wear items and software issues.
Sources: Research draws on model-specific owner forums and owner communities, recall information from official authorities, German automotive press, and multiple workshop cost references cross-checked against each other.
This report is for informational purposes only and does not constitute professional advice. Estimates may be inaccurate. Always have a qualified specialist inspect the vehicle before purchase. We accept no liability for decisions made based on this information.
