What causes a SPN 4902 code?

SPN 4902 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 4902 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4902 active.

How do I fix SPN 4902?

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 4902

Allison transmission code P4902

What it means

Transmission Control Module (TCM) Internal Processor Fault. This is a logic-side error indicating the TCM has detected an internal hardware failure preventing proper operation.