U0421
Invalid Data Received From Suspension Control Module A
Communication network
Generic OBD-II
Low
What it means
U0421 is a network communication code: a module is receiving data from the suspension control module that is implausible, out of range, or corrupt. Communication itself is working, but the values are wrong. It usually affects an adaptive or air-suspension feature, which defaults to a safe fixed setting, so the main impact is ride quality rather than basic vehicle control.
Low
Can I keep driving? Generally drivable — adaptive or air suspension may default to a fixed setting, affecting ride quality but not basic control.
Common symptoms
What you'll notice
- Suspension or ride-control warning light or message
- Firmer, harsher, or uneven ride as adaptive damping defaults
- On air suspension, ride height may not adjust or may sag
- Other network warning lights may appear at the same time
Common causes
Most likely first
- Internal fault in the suspension control module sending corrupt dataLikely
- Damaged wiring or connectors on the communication bus to the moduleCommon
- Low system voltage or a poor ground affecting module outputCommon
- Failed ride-height or suspension sensor feeding bad values to the moduleLess often
How to diagnose & fix
Work through it in order
- Scan all modules and record freeze-frame data; clear any lost-communication codes first.
- Check battery voltage and ground connections at the suspension module.
- Inspect the module's wiring and connectors on the CAN bus for corrosion or damage.
- Check the ride-height and related suspension sensors for range faults.
- If wiring, power, and sensors are good, suspect the suspension control module and confirm with manufacturer tests.
FAQ
Quick answers
Is it safe to drive with U0421?+
Usually yes for normal driving. The suspension typically falls back to a safe fixed mode, so ride comfort and handling suffer but basic control remains. On air suspension, watch for the car sagging.
Can I just clear U0421?+
Clearing hides the warning temporarily, but it returns while the module keeps reporting bad data. Diagnose the wiring or module first.
Related codes
Often seen with U0421
Read & clear U0421 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX