Powertrain, generic (extended)

P22A8 NOx Sensor Heater Sense Circuit Low (Bank 1 Sensor 2)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P22A8 means the heater sense line of the rear NOx sensor on bank 1 is shorted to ground; the sensor module uses that line to read the element temperature via its resistance. With that line pulled to ground, the module sees a temperature value it cannot trust and cannot regulate the heater properly. GM documents the test on the 3.0L LZ0: ground short at the HTemp pin, judged with dew point reached and sensor supply above 9.9 V, 80 failures in 160 samples, Type B after two trips; the Continental Gen 3.5 sensor debounces such faults internally for 1.5 s. GM's 2017 small diesels use the same check with 20 failures in 40 samples. No public bulletin names this code. P22A6 is the open circuit, P22A9 the short to voltage, P2210 the front sensor.

Likely causes

Heater sense conductor shorted to ground inside the probe
Probe lead insulation damaged against exhaust or body
Water bridging pins in the probe connector

Symptoms

  • Malfunction indicator lamp on after two trips
  • Outlet NOx sensor not ready
  • SCR efficiency check does not run

Repair estimate

DifficultyMediumDIY possible
Parts and labour€150–1,000
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

nox sensornox sensor heater

Related codes

P22A6P22A7P22A9P22AAP2210

References: gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.