Volvo 850 — ABS warning light repair

The most common cause is poor solder joints on the ABS control module (ECU box), not a faulty sensor. Symptoms: error code 'weak signal' even though sensors are intact, and the fault usually disappears on the next start.

You need open wrenches, an E5 Torx socket, needle-nose pliers, sealant adhesive, and lacquer. The ABS box is located between the air filter housing and the fuse box. Disconnect the battery, main fuse, air mass meter, and air filter housing to access the box.

Open the module cover and visually inspect the solder joints. Re-solder suspicious areas and protect the solder with lacquer. Reseal the cover with adhesive. The repair works with basic tools and is 99.9% likely to be in the box, not the sensors.