CarScan
C0121Chassis

ABS valve circuit malfunction

Where to start

The ABS valve circuit. As with C0110, power, earth and the unit's connector come first; talk of replacing the hydraulic unit comes after. ⚠️ It is worth knowing that ordinary braking still works with this code: only ABS switches off and the pedal feels as it did. The danger is elsewhere — on a slippery road the car stops saving you from locked wheels, while the ABS lamp stays lit and people stop noticing it. A common cause is not the valve itself but the hydraulic unit's connector: it sits low and collects salt and moisture. Before replacing the unit, unplug the connector, dry it and look for green corrosion.

A code is not a diagnosis. It says which check failed, not which part to replace. Clearing it without repair only means the car will report it again in a few trips.

How to put together a report a mechanic will actually read

How the code is built

Letter — the systemChassis: brakes, ABS, suspension
Common or the maker's ownGeneric code: the same on every car
Number of the faultThe serial number inside that group — it does not say how serious the fault is

All codes in «Brakes, ABS and stability control»

How the app helps

CarScan reads this code from your car through an OBD-II adapter, shows whether it is active now or only stored, names the module that reported it, and puts it into a plain-text report for your mechanic.

See what the app does

Unfamiliar word? Open the glossary

What the letter and the four digits mean