P23C2

Code

Generic P — Powertrain

NOx Sensor Delayed Response - High to Low Bank 1 Sensor 3

Brand: Generic

Type: P — Powertrain

Views: UK: 22 EN: 32 RU: 22

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Aging or contaminated NOx sensor (soot, deposits)
Heater circuit failure (open, short, or intermittent)
Wiring or connector damage, corrosion, high resistance or intermittent connection
Exhaust leaks upstream of the sensor altering readings
Sensor mounted incorrectly or wrong sensor installed
PCM/ECU fault or software/calibration issue

Check Engine Light (MIL) illuminated, P23C2 stored
Delayed or abnormal NOx sensor voltage/response on live-data during transitions
Failed emissions or NOx-related emissions test
Possible reduced aftertreatment performance, regeneration or SCR dosing anomalies
Occasional limp-home mode or reduced engine performance in some systems

Read DTCs and freeze frame / live data; record related codes (heater, ECM, SCR codes)
Visually inspect sensor, connector and wiring for heat damage, corrosion, soot or pin damage
Check for exhaust leaks upstream of the sensor and correct if found
Monitor NOx sensor raw signal and compare to reference sensors or expected behavior while engine transitions from high to low NOx output (load changes, throttle lift)
Verify heater supply and ground presence with key on/engine running
Measure heater resistance and compare to service manual or expected range

Expected: sensor output changes quickly when NOx concentration changes (manufacturer-specified response time; typically rapid — seconds or less)
Typical electrical: sensor signal is an analog/frequency-type output referenced to ECU (varies by manufacturer) — check service manual for exact voltage/frequency range
Heater circuit: supply is typically 12 V switched by PCM; heater current/heater resistance specified in service data
When NOx falls from high to low the sensor output should fall smoothly within the specified response window; excessive lag indicates slow sensor chemistry or electrical problem

Retrieve all DTCs and freeze frame; note conditions when fault set (temp, load, RPM).
Perform a visual inspection of Bank 1 Sensor 3, connector and wiring; repair any damaged wiring or corroded terminals.
Verify exhaust integrity upstream of the sensor; repair leaks and retest.
Check heater circuit: with key on/engine running verify heater supply voltage at connector, check ground; measure heater resistance (compare to service spec).
Backprobe sensor signal with a scan tool while inducing a high-to-low NOx event (reduce load or throttle) and observe response time; compare to known-good sensor or published spec.
Perform wiggle and continuity tests on harness to reveal intermittents. Inspect shielding/grounding if present.
If electricals OK but response slow, remove sensor and inspect for contamination/sooting; replace sensor if contaminated or out of spec.
If replacement does not clear code, check upstream aftertreatment components (SCR catalyst, dosing system) and PCM software/grounding. Consider ECU diagnosis if wiring and sensor are confirmed good.
Clear codes and road test to confirm repair; verify no reoccurrence and correct sensor response on live data.