What causes a SPN 661 code?

SPN 661 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 661 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 661 active.

How do I fix SPN 661?

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 661

J1939 SPN 661 — Engine Management parameter

What it means

Engine Compression Brake Control: The ECU detects an open circuit, short to ground, or data mismatch regarding the engine brake's commanded state versus its actual state.