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Diagnostic trouble code U0421 indicates: Invalid Data Received From Suspension Control Module A. It was set by your vehicle's onboard diagnostics system and will typically keep the check engine light on until it's addressed.
Which ECUs store U0421 is read from your file during analysis. DTC Removal is available on supported ECUs for these makes:
Upload your ECU file and DTC Doctor will detect this code (and any others) automatically, then remove it for good — no dealer visit, no guesswork.
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