U0421Invalid Data Received From Suspension Control Module A
- Generic OBD-II code · Network
- Can trigger limp mode
- How the car detects it
- Suspension control module A runs air springs, ride height or adjustable dampers and broadcasts level and status data. U0421 tells that a receiving module gets these frames but finds them corrupt or implausible. GM spells out one receiver: in the 2025 tables the electronic brake module watches the vehicle level control frames for a frozen rolling counter or a wrong protection value, sets the fault at 8 errors in a window of 16 and does the same with 3 of 16 for the top speed limit sent by the automatic level control; all are Type C, so no MIL. FCA documents U0421 on 2019-2020 Ram 2500/3500 with air suspension: before an air suspension module is replaced, pull its 20 A fuse F50, clear U0132, U0421 and U0422 and road test, and replace only if they return. Ride height may stay fixed. U0132 is lost contact.
- What you may notice
- Service air suspension or leveling warning
- Ride height no longer adjusts
- Stability or brake system message alongside
- Likely causes
- LikelySuspension module software hang, cleared by a power reset
- PossibleLow supply voltage or weak battery during start-up
- RareInternal fault of the suspension control module
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €50 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.