What causes a SPN 612 code?

SPN 612 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 612 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 612 active.

How do I fix SPN 612?

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 612

Magnetic Speed Sensor Signal Intermittent or Lost

What it means

The engine control module (ECM) monitors the crankshaft or transmission input speed sensor signal. SPN 612 indicates that the pulse frequency is missing, erratic, or out of range while the engine is expected to be running.