P208A: Why the DEF pump may stop before an open circuit is identified

P208A identifies an open in a reductant pump motor control circuit in this documented GM system. The pump uses three motor phases, and the diagnostic must distinguish a general operating anomaly from the specific electrical failure mode.

The running observation is only the first stage

During operation, the controller expects back electromotive force feedback at each 60-degree interval. Missing that feedback prompts a transition to an off-line state. The table explicitly says that the precise fault cannot be isolated while the pump remains on.

Once the pump is off, an internal driver diagnostic status identifies the open-circuit condition. The listed failure confirmation uses forty 0.01-second samples. Thus, the pump being commanded off can be a deliberate diagnostic response rather than evidence that no electrical test is being performed.

Distinguish an open path from poor pumping

A pump that fails to deliver pressure and a driver that reports an open phase are different observations. The latter is the evidence associated with this code. The source does not identify which external connection, winding or internal driver element is responsible.

Record the online-to-offline transition, driver status and related faults together. The monitor requires active vehicle power mode and excludes specified internal controller faults; recovery is described as occurring on the next driving cycle. An immediate restart attempt is consequently not equivalent to successful completion of the prescribed diagnostic. Use the applicable motor-circuit procedure to locate the fault without improvising phase energization.

Source and scope

2025 GM 25OBDG04B DEFC monitor calibration only; this document does not establish applicability to every model, engine or reductant system. These are documented monitor criteria, not a universal repair procedure. GM PDF, physical page 192.