U0421

Invalid Data Received From Suspension Control Module A

Q: 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.

Q: 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.

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.

Real-world scan data

Seen in

scans in the past year

Found in

<0.1%

of scans

<0.1%

of scans that found faults

Appears alongside · share of U0421 scans

U0416in 73.3% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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.

Read & clear U0421 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX