Where is the flasher unit on a 2001 Volvo S40?

The flasher unit on a 2001 Volvo S40 is typically located inside the fuse box under the dashboard, on the driver's side. However, it's not always a separate easily identifiable unit like in older cars. It's more likely integrated into the central electronic control module within that fuse box. Therefore, you won't find a single replaceable flasher relay. If you have a flashing problem, the issue is more likely to be a faulty switch, wiring, or a problem within the body control module itself, rather than a replaceable flasher unit. You'll need a Volvo specific wiring diagram or a visit to a qualified mechanic to diagnose the problem accurately.