P2208: NOx heater-sense open circuit is separate from heater control

P2208 concerns the heater-sense connection of NOx sensor 1 in the reviewed GM source. The table names it HTemp and describes an open circuit on the resistance-measurement path. This differs from an open circuit in the heater-control connection.

Why a heater can need a separate sense diagnosis

The monitor's question is whether the sensing connection is electrically intact, not whether a commanded heater circuit has continuity or whether the exhaust contains a particular NOx concentration. A general “heater works” observation does not independently validate the resistance-sense path.

The source adds a hardware-specific detail: Continental generation 3.5 NOx sensors include an internal 1.5-second debounce for electrical-fault reporting to identify the affected wire condition. That internal stage should be distinguished from the ECM's own sample counter, and should not be assumed for every sensor using P2208.

Enabled check and confirmation

The table requires the bus relay on, relay voltage above 11 volts, sensor supply above 9.90 volts, and valid CAN communication and data. It lists 80 failing samples within 160 at 25 milliseconds per task. Reporting is Type A over one trip.

Verification should allow the relevant sensor-internal reporting and controller qualification to complete with valid communication. An immediately absent status after reconnection does not necessarily show that both stages passed. The page gives no physical HTemp pin number or replacement instruction. Confirm the installed hardware and vehicle-specific service procedure before applying these 2025 GM monitor details.

Source: GM monitor, PDF page 1413.