What causes a SPN 166 code?

SPN 166 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 166 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with SPN 166 active.

How do I fix SPN 166?

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 166

SPN 166 Engine Rated Power Special Instructions

What it means

This parameter indicates the engine's output power capability and is used by the vehicle's electronic control modules to determine shifting strategies and torque management.