Hearing a brief motor whir or buzz from the ABS unit when you start the car or pull away can be alarming - but it is often normal. Here is why the ABS pump runs after startup.
The self-test is normal
Many vehicles run a quick ABS self-test when you start up or first reach a few mph - the pump and valves cycle to confirm they work, making a brief whir or clunk; see ABS pump noise and how ABS works. This is routine and lasts a second or two.
When it is expected
A short self-test noise once per drive cycle, with no warning light, is normal for many cars. It is the system checking itself - nothing to worry about.
When it is a problem
If the pump runs for a long time, runs repeatedly, or comes with an ABS warning light, that points to a fault - a leaking valve, a pressure problem, or a failing pump; see ABS operation. Constant pump running is not normal.
What to do
A brief startup self-test needs no action. Persistent pump noise or a warning light means have the ABS scanned. Keep the base brakes strong with quality pads and hardware.