What causes a P2056 code?

P2056 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 P2056 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P2056 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

P2056

Reductant Injection Valve Circuit Open Bank 2 Unit 1

What it means

The engine control module (ECM) detects an electrical open circuit in the control line for the secondary DEF (Diesel Exhaust Fluid) injector, typically used in dual-bank or high-horsepower aftertreatment systems.