What causes a P187B code?

P187B 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 P187B code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P187B 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

P187B

Coolant pump speed sensor out of range high

What it means

The Engine Control Unit (ECU) has detected that the speed signal feedback from the coolant pump (usually the fan clutch/water pump assembly in modern Paccar/Cummins applications) is higher than the commanded or physically possible range.