What causes a U0939 code?

U0939 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 U0939 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with U0939 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

OBD-II

U0939

Network/CAN bus communication code U0939

What it means

Invalid data received from the Remote Keyless Entry (RKE) module. The main controller cannot interpret data regarding door locks or remote start commands.