Powertrain, generic (extended)

P23B7 NOx Sensor Heater Control Circuit Range/Performance (Bank 1 Sensor 3)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P23B7 is set when the heater drive of NOx sensor 3 on bank 1 looks electrically sound but does not behave as the control strategy expects, for instance a heater duty cycle far from what the element should need to reach operating temperature. No manufacturer documents P23B7 publicly; GM's 2025 table covers sensor 3 only with the plain heater circuit codes P23B1-P23B3 and the resistance check P23B5. Ford's 2023 diesel summary shows how the front-sensor counterpart P220E is judged: apart from open and shorted heaters a heater whose duty cycle misses the expected figure by over 20 percent is also treated as faulty. CARB requires sensor heater performance to stay within the supplier's limits. If the element never gets hot enough, sensor 3 stays inactive; P220F is the sensor 2 version.

Likely causes

Aged heater element that needs far more or less power than expected
High resistance in heater supply or ground contacts
Sensor supply voltage at the lower limit, so the heater cannot keep up

Symptoms

  • Check engine light on
  • Sensor 3 takes long to become ready or drops out of its active state
  • SCR efficiency monitor not completing

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–900
Time0.5–2.5 h

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

Parts involved

nox sensor b1s3 heater

Related codes

P23B1P23B2P23B3P23B5P220EP220F

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