Powertrain, generic (extended)

P23B5 NOx Sensor Heater Sense Circuit Range/Performance (Bank 1 Sensor 3)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P23B5 says the heater feedback from NOx sensor 3 (bank 1) is present but implausible: the element does not reach or hold the resistance that matches its target temperature. GM's 2025 diesel table 25OBDG04B compares the raw heater resistance of the post-second-catalyst sensor with its target and fails it outside a relative band of 0.06, after waiting 200 s from supply in range and from dew point; 125 of 250 samples, Type A. Ford lists P23B5 for 2023 Super Duty trucks with the 6.7L diesel together with P2209, P22A7 and NOx sensor communication codes (SSM 51750, 51791): harness 14406 chafes on the right-hand EGR cooler near connector C146, so fuse F18 (20 A) is checked first. P23B4 is the open sense line.

Likely causes

NOx sensor harness chafing on a hot component such as the EGR cooler (Ford 2023 6.7L)
Aged heater element whose resistance no longer matches the target
Blown fuse in the NOx sensor supply after a short
High contact resistance in the heater connector

Symptoms

  • Check engine light after one trip
  • Several NOx sensor and communication codes at once
  • SCR warning, sensor 3 not ready

Repair estimate

DifficultyMediumDIY possible
Parts and labour€20–1,000
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

P23B4P23B7P2209P22A7U029D

References: gsi.ext.gm.com, static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.