Mercedes-AMG A45 S

A very hot hatch, carefully bought

The Mercedes-AMG A45 S is the W177-generation hot hatch that turned a sensible five-door body into a genuine junior supercar rival. Our catalogue covers the 2020-on car with a 2.0L Turbo Inline-4, 421 bhp, 500 Nm, 0 to 100 km/h in 3.9 seconds and a 270 km/h maximum, all through all-wheel drive. We have not driven this model for this article. This is a desk-researched ownership guide using Mercedes-Benz media material, the PistonHeads A45 S used buying guide and the DVSA recall service. The first thing to understand is that this is a highly boosted small engine in a compact body. It is fast, but it rewards careful checking more than bravado.

Mercedes-Benz's own final-edition material confirms the important hardware: the M139 engine, 421 hp, 500 Nm, the eight-speed AMG SPEEDSHIFT dual-clutch gearbox and 4MATIC+ with AMG Torque Control. PistonHeads places the same basic package in the real world: a 0-62 mph time of 3.9 seconds, strong mid-range thrust and the slightly surreal experience of supercar pace in a hatchback. The catalogue's 421 bhp and 500 Nm match the quoted outputs closely. What matters more is condition. A low-mileage car with patchy servicing is a worse buy than a higher-mileage car with evidence of disciplined maintenance.

The M139 engine needs cooling discipline

The M139 remains one of the most extreme production four-cylinder engines. PistonHeads describes the power delivery as more linear than the old A45, but the hardware is still working near recognised limits. That means oil level checks, careful warm-up, sensible cool-down after hard use and close attention to seals and gaskets. Turbo engines do not need superstition, but they do need clean oil and time to shed heat after a hard run. Ask how the car has been used. A car that has seen repeated drag strip runs or track days needs a deeper file than one used for fast road commuting.

Listen for rattles or unusual mechanical noise on start-up, then check the engine under load and again when hot. A healthy M139 should pull cleanly without hesitation, smoke or warning lights. The PistonHeads guide mentions an Australian recall for faulty spark plugs on a small number of 2020-built cars. That is a market-specific note rather than proof of a global defect, but it reinforces the need to check recall status by VIN and ask for the work history. Any engine-management light, misfire history or unexplained plug change should be documented.

Gearbox behaviour is part of the test drive

The eight-speed dual-clutch gearbox can feel alert and very quick, but it is not always seamless. PistonHeads notes that the closely stacked ratios reward good timing in manual mode and that the gearbox can be slow to react to a demand for reverse. In traffic, small hesitations or shuffles may be normal; violent shuddering, slipping or refusal to engage is not. Drive the car from cold and fully warm. Check low-speed manoeuvres, parking behaviour, reverse engagement and full-throttle upshifts.

Modifications deserve caution. The A45 S is already highly tuned, and anonymous engine or gearbox software can mask problems rather than solve them. If the car has been mapped, ask for the tuner, the supporting hardware, logs and proof that the gearbox strategy was considered. Standard cars are not automatically risk-free, but a documented standard car is easier to assess. Fresh fluid at the correct interval is more useful than a seller's claim that the box is sealed for life.

4MATIC+, Ride Control and the rear-axle checks

The A45 S uses 4MATIC+ all-wheel drive with a mechanical sport differential at the rear. In normal driving it provides huge grip; in the right mode it can send substantial torque rearward and help rotate the car. That makes tyre condition and alignment especially important. Check for uneven wear, mismatched brands and any evidence of kerb damage. The steering should feel precise without excessive tramlining. If the car has AMG Ride Control adaptive suspension, confirm that the modes change the damping as intended and that there are no suspension fault messages.

PistonHeads reports recall activity in late 2024 for unusual rear-end noises, with a rear flex disk and shield replacement carried out free by dealers. This is exactly the sort of campaign that should appear in the service record. Also ask about any history of suspension malfunction messages. Some cars have displayed warnings advising reduced speed. A stored message without a matching invoice is a negotiating point; an unresolved active warning is a reason to pause. The A45 S came with 19-inch wheels as standard, so inspect the wheels for cracks and the brakes for disc condition, pad life and evidence of hard use.

Body, cabin and electrical details

The A45 S was only sold as a five-door hatchback, so the body style is not the issue; condition is. Check the front bumper and bonnet for stone damage, the doors for consistent gaps and the rear hatch for water ingress. Inside, the W177 cabin is dominated by twin screens and AMG-specific displays. Test everything: infotainment response, driver-display modes, climate control, seat adjustment, steering wheel controls and every driver assistance feature. Intermittent electrical gremlins on a modern Mercedes can be expensive if they require module diagnosis.

Look beyond the screens. Listen for rattles from the dashboard, door cards or rear load area on a rough road. Check the parking sensors, camera, puddle lights and door sealing. A car with repeated flat batteries may have more than an old battery; low voltage can create a cascade of module faults. Ask for a battery test and a scan with a capable diagnostic tool. The goal is not to fear electronics, but to avoid inheriting a car whose faults have been cleared rather than repaired.

Service history decides the purchase

The best A45 S is a car with a documented service book, consistent mileage, no unresolved warnings and proof that recall work has been completed. Use the DVSA recall service as a starting point, then confirm with invoices. Check for accident repair, paintwork differences and signs of track use such as worn tyres, heat-marked discs or missing underbody panels. A proper test drive should include a cold start, urban crawling, a fast merge and a sustained motorway run. The A45 S is a remarkable hot hatch, but its performance is only enjoyable when the cooling, gearbox, suspension and electronics have been maintained with the same seriousness that AMG engineered into it.