What it means
Fault in the valve-relay circuit that powers the ABS hydraulic solenoids. The EBCM monitors relay command vs. feedback; discrepancies (open/short/relay stuck) set C0121. Corvette Forum+1
Symptoms
- ABS lamp on; ABS/ESC disabled; may set alongside other ABS DTCs. Corvette Forum
Common causes
- Failed valve relay or corroded relay socket; blown/poor fuses or EBCM power/ground.
- Open/short in the relay control/feedback circuits; internal EBCM fault. Corvette Forum
Diagnostic notes / fixes
- Check fuses/relay and EBCM power/grounds; verify command and feedback at the relay.
- Repair wiring; replace relay. If the circuit proves good and the DTC persists, suspect the EBCM. Corvette Forum