U0421: Invalid Data Received From Suspension Control Module A

What it means

A control module received data from Suspension Control Module A that it judged invalid or implausible. This code identifies the rejected data, but does not by itself identify the cause.

How it works

Suspension Control Module A manages or reports data for the vehicle's controlled suspension system. U0421 sets when another module considers data from suspension module A implausible; it does not identify a specific failed suspension part.

Common causes

Most likely first.

1. Fault or implausible input at Suspension Control Module A
2. Damaged or loose network wiring or connector
3. Module power, ground, or programming issue

Symptoms

• Suspension warning message
• Suspension-related functions may be limited
• Other communication codes

How to diagnose it

1. Scan all modules and record freeze-frame, suspension, and network codes to determine whether the fault affects module A alone or several modules.
2. Check for suspension warnings, unusual ride height, harshness, or handling changes, noting that the code names module A specifically.
3. Inspect module A's connectors and wiring for loose fit, corrosion, water intrusion, or damage along the suspension harness.
4. Check module A power and ground circuits against the manufacturer's specification before investigating suspension components.
5. Compare live suspension module A data with related sensor readings, then test network communication and the named module circuits to the manufacturer's specification.
6. If supply and wiring pass, check for applicable suspension module software or calibration updates.

Common fixes

• Reseat or repair a loose or corroded module A connector.
• Repair damaged wiring to Suspension Control Module A.
• Restore the module's power or ground supply.
• Apply an applicable software or calibration update.
• Replace module A if its circuits and inputs are sound but its reported data remains invalid.

Can I keep driving?

If ride height, steering, or handling has changed, avoid high speeds and rough roads and have the suspension checked promptly. Stop driving if the vehicle is unstable or a wheel appears to be contacting the body.