Volvo S40

The timing belt tensioner of the B4164S2 tends to fail when the change interval is neglected. If the belt snaps, valves bend immediately — costly total damage despite an inexpensive engine.

Symptoms: Rattling noise on cold start, belt visibly frayed or cracked on visual inspection

The plastic thermostat housing of the B4164S2 can crack on older vehicles or lose its O-ring seal. Unexplained coolant loss should always include the thermostat housing in the inspection.

Symptoms: Slight coolant loss, damp area at thermostat housing, engine temperature rises in high ambient temperatures

The plastic connectors on the B4164S2 injectors become brittle over time and break on removal. Loose contacts cause misfires on individual cylinders.

Symptoms: Sporadic misfires, rough idle, fault message for individual cylinders

Individual ignition coils on the B4164S2 fail at high mileages or with temperature cycling. The engine then runs on three cylinders with noticeable power loss and increased consumption.

Symptoms: Misfires and hesitation, increased fuel consumption, check engine light with cylinder fault code

The brake lines in the engine bay of the S40/V40 I corrode severely with age, which can cause brake fluid loss. Porous brake hoses and seized rear brake calipers were also regularly found.

MOT inspectors flag worn ball joints and tie rod ends on the S40/V40 I front axle significantly more often than average. The cause is high structural loading on the axle components.

Dirt and moisture accumulate behind the front wing; foam stuffing absorbs water and keeps it permanently against the metalwork. Sills and rear wheel arches are the most common rust spots.

The thermostat in the first-generation Volvo S40/V40 frequently sticks, leading to overheating or excessively low operating temperatures. Coolant loss indicates sealing problems.

Springs break on the front and rear axles of the S40 II, V50 and C30 comparatively often, as MOT inspectors regularly find. The repair is straightforward but not cheap.

Alternator and starter motor fail relatively early on models built before 2005. Sudden power cuts or starting problems are typical symptoms. Replacement costs €400–700.

Door locking motors fail and produce metallic noises when closing. All doors can be affected; repair costs around €200 per door.

The thermostat is prone to malfunction and can cause excessively high or low operating temperatures. Coolant loss without a visible leak point to early cylinder head issues.