Code result
U0004
High Speed CAN Communication Bus Low
High severity
What it means
The CAN-High signal stays below its valid voltage window. Common cause is a short to ground on the CAN-H wire or a transceiver that pulls the line down. The bus stops working until the offending node is isolated.
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
CAN-High shorted to ground
highOne of the most commonly reported causes for this code — check this first.
Internal transceiver failure on a node
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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