C0121
Valve Relay Circuit
What it means
C0121. Valve Relay Circuit. This Chevy-enhanced code applies to Silverado, Sierra, Tahoe, Yukon, Suburban.
Findings, check these first
- Failed valve relay inside the EBCM
- Corroded EBCM electrical connector pins
- Low system voltage preventing relay pull-in
- Internal EBCM circuit board failure
- Water intrusion into the EBCM housing
Standard procedure
- Verify battery voltage is normal before diagnosing
- Inspect the EBCM connector for green corrosion and backed-out pins
- Test the valve relay circuit per GM service information
- Check EBCM powers and grounds under load
- Replace the EBCM if the relay circuit tests open with good feeds
Look up another code
Press / to jump to the box. Chevy-enhanced powertrain, body, chassis and network codes.
Sources and review
Review: no source links are recorded for this entry.
Review note: spot check found no fetchable public reference page; no contradictory evidence; retained under the scoped ruling; first recheck candidate when live sources return.
Last updated 2026-09-25.
Report a correction for C0121. Include your vehicle, the issue and a source if you have one.
This fault is part of the GM ABS and StabiliTrak family. The GM ABS and StabiliTrak codes guide covers the check order.