P23BB NOx Sensor Heater Resistance (Bank 1 Sensor 3)

P23BB says the heater element of NOx sensor 3 on bank 1 has a resistance outside its permitted band. Because the resistance of the ceramic heater climbs with temperature, it doubles as the thermometer of the probe, so an aged or cracked element heats poorly and reports a false temperature as well. No manufacturer publishes P23BB. GM runs the same kind of check on the post-second-catalyst sensor in 25OBDG04B but stores P23B5: the raw resistance may differ from its target by no more than 0.06 in relative terms, tested once supply and dew point have been valid for 200 s, 125 of 250 samples, Type A. Under CARB, the heater must be watched against the limits its supplier guarantees. P224A and P224B are the same fault on sensors 1 and 2; the usual remedy is a new sensor.

Likely causes

Symptoms

• Check engine light on
• Sensor 3 slow to become ready after a cold start
• Implausible NOx readings from the rear sensor

Repair estimate

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

Parts involved

Related codes

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