What causes a U0066 code?

U0066 can be triggered by several issues — see the verified probable causes and step-by-step diagnostics shared by mechanics and owners on OBDIY.

Can I drive with a U0066 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with U0066 active.

Follow the step-by-step diagnostic on this page, then read the verified fixes contributed by other Heavy Truck owners — the answer marked "Verified Cause" worked for the original poster.

OBDIY

Log in Sign up

OBD-II

U0066

Control Module Communication Bus G High

What it means

Voltage on Bus G exceeds the standard CAN-High/Low limits, typically due to a short to 12V or 24V supply.

Sign in to view symptoms, probable causes, diagnostic steps, severity, and related codes

Log in Sign up free