P22A5: NOx sensor 2 heater-control short to supply

In this GM monitor, P22A5 means the post-catalyst NOx sensor reports a short to power on its heater-control pin. The generic “circuit high” label describes that electrical fault category. It is not a heater-temperature maximum or an exhaust concentration limit.

What must happen before reporting

The sensor bus relay must be commanded on, its supply must exceed 9.90 V and powertrain relay voltage must exceed 11 V. The sensor must also have reached dewpoint. Both missing CAN communication and invalid CAN data block this particular check. An 80-of-160 counter runs on a 25 ms task, with Type B, two-trip reporting.

These qualifications matter when a fault appears only after warm-up. The delay can reflect when the monitor becomes eligible, rather than proving that temperature caused a wire to fail.

Separating related fault paths

Heater control and heater resistance sensing have separate entries in the source. A heater-control short-to-power report directs the diagnosis to the control path; it does not independently establish an HTemp sense-circuit fault. Use the exact service information to identify those paths and assess the reported condition.

After corrective work, confirm that valid sensor reporting returns and that the enabled heater-control test no longer detects the fault. The source provides no universal terminal voltage, connector location or automatic sensor-replacement instruction.

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 1432.