What causes a P151A code?

P151A 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 P151A code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P151A active.

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

OBD-II

P151A

DEFOI vehicle speed limit fault

What it means

DEFOI (Diesel Exhaust Fluid Operator Inducement) Vehicle Speed Limit Fault. This is a strategy-driven code indicating the vehicle's road speed is being limited to 5 mph (or a similar crawl speed) because a major emissions fault has gone unaddressed.