Code result
U0304
Invalid Data Received from Transmission Control Module
High severity
What it means
The ECU receives messages from the TCM but their content is implausible (e.g. invalid gear, impossible speed). The transmission may switch to limp-home mode and shift quality is degraded.
Is it safe to drive?
No — stop driving
This code can put the vehicle into limp or reduced-power mode. Avoid extended driving and have the vehicle diagnosed promptly.
Most likely causes
Software version mismatch after replacement
mediumA plausible cause — test and verify before replacing parts.
TCM partially failing
mediumA plausible cause — test and verify before replacing parts.
Gateway module routing CAN messages incorrectly
lowLess common, but worth ruling out after the more likely causes.
Related help
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