What causes a SPN 520303 code?

SPN 520303 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 520303 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 520303 active.

How do I fix SPN 520303?

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 520303

Accelerator Pedal Position Sensor

What it means

Indicates an issue with the accelerator pedal position sensor, which reports pedal input to the ECM. A faulty sensor leads to erratic engine speed or no throttle response.