What causes a SPN 4203 code?

SPN 4203 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 4203 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 4203 active.

How do I fix SPN 4203?

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 4203

Allison transmission code P4203

What it means

Transmission Clutch Slip Detected - Specifically related to a gear ratio mismatch while the transmission is attempting to apply or hold the C2/C3 clutch packs.