What causes a U0811 code?

U0811 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 U0811 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with U0811 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

U0811

Network/CAN bus communication code U0811

What it means

Communication lost with the Climate Control Module (HVAC) on the CAN bus. The vehicle's main computer cannot send or receive data from the heater/air conditioning system.