C0121
ABS / stability-control fault code, listed for 1 vehicle line from Chevrolet. What it means on each one, with sources, and when the module is the cause.
What C0121 means
Valve Relay Circuit (Malfunction)
On: 1999-2006 Chevrolet Silverado 1500 / 2500 (GMT800)
Is it the ABS module?
Check the cheap things first: battery voltage and the main fuses for the ABS pump and module, the ground straps, the module connector (corrosion, a pushed-back pin) and, for wheel-speed codes, the sensor and its wiring at each wheel. If those are good and the code returns as soon as it is cleared — or the scan tool cannot talk to the ABS module at all — the module itself is the likely cause, and that is what we repair.
Vehicles that set C0121
C0121 by vehicle
What does C0121 mean on a Chevrolet Silverado 1500 / 2500 (GMT800)?
The source we cite for the 1999-2006 Chevrolet Silverado 1500 / 2500 (GMT800) lists it as: Valve Relay Circuit (Malfunction). That vehicle uses Kelsey-Hayes EBC325 (Kelsey Hayes 325 EBCM). We repair it as part of the Kelsey-Hayes EBC325 family, from $499.
Still not sure?
Send us C0121, a photo of the module label and your VIN — we tell you whether the module is the likely cause and what it costs, before you pull anything. Asking costs nothing.
C0121 keeps coming back after the checks? Fix the module — from $499.
Look up your part number and order online — we email you a prepaid label to our lab. Or send us a photo of the label and your VIN first, and we'll tell you what you have and what it costs.
Back with your VIN and coding · can’t be repaired? repair price back, minus shipping · 1-year warranty · rush 2–3 days +$100
Call (817) 505-4201 · 📱 Text us a photo of the module label · Ask first — send a label photo · Email repairs@absmodulelab.com