P23B8: NOx sensor 3 heater-sense path shorted to ground

P23B8 names the low-voltage failure of NOx sensor 3 heater sensing. The source specifies a short to ground at HTemp, the resistance-measurement connection. This is feedback-circuit evidence, not an indication that the exhaust is too cold.

Conditions behind the report

The bus relay must be on, sensor supply above 9.90 V and powertrain relay voltage above 11 V. Dewpoint must have been reached, with neither communication loss nor invalid CAN data. The ECM counts 80 failures out of 160 samples at 25 ms intervals and assigns Type B, two-trip reporting.

An additional 1.5-second internal electrical-fault debounce is documented for Continental generation 3.5 sensors. It helps explain delayed identification within that sensor family but does not supply a universal timing specification.

Interpreting the next check

Separate this HTemp path from the heater-control ground-short diagnosis P23B2. A successful command to the heater does not test the resistance-sense circuit. Follow the correct wiring information and examine the reported sense fault under qualified conditions. During verification, confirm both valid reporting and completion of the sense-circuit check after dewpoint. A normal-looking NOx ppm value alone cannot establish that the monitored feedback circuit has recovered, and the table does not prescribe replacement of a particular assembly.

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 1462.