Code Definition

U2021 — Invalid /fault data received (Non SCP)

System: Network Communication  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About U2021

U2021 is a generic (obd-ii standard) network communication diagnostic trouble code. It belongs to the U-prefix family of codes, which covers inter-module network communication (CAN, LIN, FlexRay, or similar) faults.

Scanning & clearing: Network (U) codes report communication faults between modules. When diagnosing U-codes, checking the vehicle's CAN bus integrity, supply/ground at each module, and reading all modules for related faults is usually the first step.

Because U2021 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

This DTC is set by a receiving control module when it takes in invalid, corrupt, or out of range data from another module over a non SCP network, typically CAN, LIN, or MOST. The received messages fail the module internal validation, such as a checksum or rolling count error, a plausibility check, or a format mismatch, so the module rejects the data. Depending on what data is affected, the module may disable a function or fall back to a fail safe default rather than act on bad information. The driver may notice a warning light, a feature working in a reduced or default mode, or related codes i...

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