What causes a SPN 39 code?

SPN 39 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 39 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 39 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

J1939 SPN

SPN 39

J1939 SPN 39 — Engine parameter

What it means

SPN 39 indicates a fault in the Starter Motor Relay Control circuit. The ECM has detected an essence of improper voltage (open circuit, short to ground, or short to battery) when attempting to engage the starter.