What causes a P1504 code?

P1504 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 P1504 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P1504 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

P1504

Vehicle speed pulse width modulated duty cycle

What it means

The ECM has detected a signal from the Vehicle Speed Sensor that is out of the expected duty cycle range or frequency, indicating an implausible or erratic speed reading.