DEF / AdBlue warning light: meaning and what to do

What it means

Diesel exhaust fluid is low or the system has a fault. When empty, many diesels won't restart.

Can I keep driving?

Usually yes, carefully and for a short distance. The def / adblue light means something needs attention soon, so have it checked in the next few days rather than ignoring it.

What to do

Refill DEF (sold at gas stations). If it stays on after refilling, have the system checked.

On some cars it shows as text

DEFADBLUEAD BLUE

Typical repair cost (US)

$10–$1,500

Estimated range when a repair is needed; it depends on the car and the cause.

What the color tells you

Amber or yellow lights mean a system needs attention. It's usually safe to keep driving carefully, but don't put it off.