Powertrain, generic (extended)

P22A9 NOx Sensor Heater Sense Circuit High (Bank 1 Sensor 2)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P22A9 is the high-side twin of P22A8: the heater sense line of the rear NOx sensor on bank 1 has a short to supply voltage. The module then reads an element resistance that is far off and loses its temperature feedback, so it cannot hold the probe at working temperature. GM's 3.0L LZ0 looks for a battery short at the HTemp pin once dew point is reached and supply exceeds 9.9 V, 80 failures in 160 samples, Type B after two trips; the 2017 small diesels need 20 failures in 40 samples. In both cases the Continental sensor itself confirms an electrical fault before reporting it. No manufacturer bulletin mentions P22A9. A short often sits where the probe lead runs close to other powered wiring or where a connector has taken in water. P22A6 is the open circuit, P22A8 the ground short, P2211 the front sensor.

Likely causes

Heater sense conductor shorted to supply inside the probe
Probe lead touching another powered conductor
Water bridging pins in the probe connector

Symptoms

  • Malfunction indicator lamp on after two trips
  • Outlet NOx sensor not ready
  • SCR warning on the display

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

P22A6P22A7P22A8P22AAP2211

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