What causes a SPN 4956 code?

SPN 4956 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 4956 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4956 active.

How do I fix SPN 4956?

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 4956

Cummins fault code 4956

What it means

EGR Valve Position - Data Erratic/Intermittent/Inaccurate. This code indicates the ECM detected that the EGR valve is not reaching the commanded position or is oscillating excessively.