What causes a SPN 790 code?

SPN 790 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 SPN 790 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 790 active.

How do I fix SPN 790?

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

J1939 SPN

SPN 790

J1939 SPN 790 — Engine Management parameter

What it means

SPN 790 typically refers to an Engine Retarder Actuator / Solenoid control circuit issue. It indicates the ECM has detected an electrical malfunction (open, short, or invalid voltage) in the circuit that controls the engine compression brake or exhaust brake.