Powertrain, generic (extended)

P23BA NOx Sensor Heater Sense Circuit Intermittent (Bank 1 Sensor 3)

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

With P23BA, the heater feedback signal from the third NOx sensor of bank 1 keeps vanishing or leaping for a moment and then recovers, rather than staying broken. P23BA itself is not described in any public manufacturer document. GM's 2025 table checks this sensor only for the lasting faults P23B4, P23B8 and P23B9, while remarking that a Continental Gen 3.5 probe only passes an electrical fault on after debouncing it for 1.5 s, so very brief dropouts may never reach the engine module at all. CARB asks for continuous monitoring of exhaust gas sensor heater circuits. Smart sensors send their heater circuit status over CAN, which is where an unstable state becomes visible. Loose terminals, a cracked lead near the rear of the exhaust and moisture drawn into the plug as it cools are the usual suspects; the MIL may come and go.

Likely causes

Terminal in the sensor 3 connector with weak contact pressure
Sense lead cracked by vibration or heat and opening only at times
Moisture entering the plug through a damaged seal

Symptoms

  • Check engine light that comes and goes
  • Sensor 3 briefly leaves its ready state
  • Fault often cannot be reproduced in the workshop

Repair estimate

DifficultyMediumDIY possible
Parts and labour€20–900
Time0.5–3 h

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

Parts involved

nox sensor b1s3 heater

Related codes

P23B4P23B8P23B9P2212P22AA

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