P20FE: first DEF injector needs excessive delivery compensation

P20FE is commonly described as reductant metering unit 1 performance. The reviewed GM row calls it low reductant consumption and ties it to the first DEF injector's hydraulic delivery-performance compensation. It does not use the same evidence as an injector open-circuit or short-circuit code.

Compensation is the measured warning

The malfunction criterion is an exponentially weighted moving average of the delivery-performance compensation factor above 1.41. The source explains that compensation has become so large that the expected pressure drop no longer assures proper reductant delivery.

That is a controller inference about delivery behavior, not a direct measurement proving one exact quantity of fluid was missing. It also does not identify the responsible restriction, leakage path or component. Those causes require additional service evidence that is not supplied by this row.

Closed-loop operation must be active

The diagnostic requires closed-loop reductant-delivery-performance compensation to be active. Its function task runs at 100 milliseconds and reporting is Type A over one trip. The page does not provide a separate fixed persistence duration, so the task rate must not be presented as the complete code-setting time.

Verification should establish that the compensation loop actually operates and that its filtered factor no longer exceeds the relevant limit. A static pressure value or an electrical pass for the dosing valve does not independently demonstrate that result. This article covers only the documented 2025 GM first-injector strategy; vehicle applicability, hydraulic isolation and any repair decision need the correct service procedure.

Source: GM monitor, PDF page 784.