What causes a U0623 code?

U0623 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 U0623 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with U0623 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.

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OBD-II

U0623

Network/CAN bus communication code U0623

What it means

Lost communication with Exhaust Gas Recirculation (EGR) Control Module. The ECU cannot manage exhaust gas flow to the intake.

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