What causes a SPN 1659 code?

SPN 1659 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 1659 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 1659 active.

How do I fix SPN 1659?

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 1659

Engine Coolant System Thermostat 1 - Monitor Performance

What it means

The Engine Control Module (ECM) has detected that the engine did not reach the target operating temperature within a specified timeframe or that the thermostat responded incorrectly.