Mercedes · 2005–2026
Common Mercedes A-Class problems, and how to check them
These are the 4 faults owners and garages report most often on the Mercedes A-Class, from the most common down. For each one: what goes wrong, how to check it yourself, and the usual fix, so you know what you’re dealing with before you buy parts.
Fact-checked by a licensed car technician · last reviewed 27 September 2026
Problem 1
Mercedes A-Class: CVT gearbox control unit failure
What goes wrong
The CVT gearbox control unit fails; early (2005-2008) cars are most affected.
How to check it yourself
Read the gearbox module codes; loss of drive or a gearbox warning with communication errors points to the control unit.
The usual fix
Repair or replace the gearbox control unit and do a CVT fluid change with the correct fluid.
Signs: Transmission slipping, Harsh shifting
Problem 2
Mercedes A-Class: DPF warning and limp mode on short trips
What goes wrong
Short stop-start trips never let the particulate filter regenerate; the 1.5 CDI (a Renault engine) also has EGR and injector wear.
How to check it yourself
Read codes and the DPF soot load and pressure in live data.
The usual fix
Regenerate with a motorway drive or forced regeneration; clean or replace a filter that stays blocked; clean or replace a sticking EGR valve.
Signs: Loss of power, Check engine light
Fault codes: P2002, P2463, P244A
Problem 3
Mercedes A-Class: Jerky shifts or gearbox warning from the 7G-DCT
What goes wrong
The gearbox control unit or its software fails, or clutch adaptation drifts.
How to check it yourself
Read the gearbox codes with a Mercedes-capable tool and ask a dealer about software updates.
The usual fix
Software update and adaptation reset; replace the gearbox control unit if it’s faulty.
Signs: Harsh shifting, Transmission slipping
Problem 4
Mercedes A-Class: Timing chain stretch on the 1.6 turbo petrol
What goes wrong
The timing chain stretches, and the camshaft adjusters can rattle on a cold start.
How to check it yourself
Listen for a rattle in the first seconds after a cold start and read cam/crank correlation codes.
The usual fix
Replace the chain, tensioner, and (if noisy) camshaft adjusters.
Signs: Rattle on cold start, Check engine light
Fault codes: P0016, P0017
General guidance, not a professional inspection. Confirm faults with measurements before buying parts, and use a qualified mechanic for brakes, steering, fuel leaks, airbags, and other safety-critical work. Terms and disclaimer