What causes a U0704 code?

U0704 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 U0704 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with U0704 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

U0704

Network/CAN bus communication code U0704

What it means

Lost communication with the Fuel Pressure Regulator 'A'. The ECM can no longer command the fuel pressure regulator to maintain the common rail pressure.