P249C: reductant pressure takes too long to enter closed-loop control

P249C records failure to establish reductant-pressure closed-loop control in the expected time. The DEFC source describes line filling, pressure buildup and retries, rather than a direct test of injected reductant flow.

Why a cold system can take longer

If the tank may be frozen, the controller delays pressure buildup until a temperature-dependent defrost routine finishes. That defrost phase must not be confused with a failed buildup attempt. Once permitted, the normal line-filling allowance is 15 seconds; the source also gives a 7.5-second allowance after start/stop exit.

The documented failure sequence can take 75 seconds: three 15-second attempts separated by two 15-second pump-off waits. Estimated DEF level must exceed three liters for diagnostic reporting, and several pump, pressure, supply and communication faults can force the pump to stop. The entry is Type A, one trip.

Reading the result

Preserve pump state, defrost status, pressure target and achieved pressure together. A pump that is waiting for authorization is not equivalent to one unsuccessfully building pressure. The source reports success when closed-loop control becomes active and states recovery occurs only on the next driving cycle.

Verification therefore needs the correct state transition and recovery context. The code alone does not identify a failed pump, blocked line or injector, and this summary is not a pressurized-system disassembly procedure.

Source and application limits

This explanation covers the cited 2025 GM monitor. Confirm the vehicle and calibration in its service information before applying these limits; inclusion in this file does not establish model compatibility. GM diagnostic parameters, PDF page 206.