What causes a U0851 code?

U0851 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 U0851 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with U0851 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

U0851

Network/CAN bus communication code U0851

What it means

Lost communication with the HVAC Control Module. The network link to the climate control computer has been severed.

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