P214F: What excessive current in DEF tank heater 1 actually establishes

P214F is the high-current diagnosis for reductant heater 1, identified as the first tank heater in this GM calibration. The measurement concerns the output driver's electrical load, not a directly measured excess in fluid temperature.

A sustained electrical load triggers the monitor

The table sets the upper current boundary at 15 A and lists forty samples at a 0.1-second time base, corresponding to four seconds of failure accumulation. The relevant evidence is therefore the current history during the event, rather than one isolated value seen after the controller has reacted.

Active vehicle power mode is required, and specified internal controller faults are excluded. The document also lists many temperature, heater, supply and communication faults that can remove the heater command.

Shutdown is not proof that the circuit recovered

If PWM has already been forced to zero, the present low current may simply reflect a disabled load. It cannot reconstruct whether the preceding energized state exceeded the limit. Recovery is specifically described as occurring on the next driving cycle.

The source supports distinguishing excessive electrical demand from inadequate heat or a low-current open-path problem. It does not identify which part of the heater circuit caused that demand. Preserve requested heating, actual current and the fault sequence, then use the correct circuit procedure to isolate the cause. Applying power externally to reproduce an overcurrent condition is not a test described by this summary.

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 201.