P23B2

Code

Generic P — Powertrain

NOx Sensor Heater Control Circuit Low Bank 1 Sensor 3

Brand: Generic

Type: P — Powertrain

Views: UK: 25 EN: 58 RU: 29

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Page language: EN

Causes

Open circuit in heater supply or ground (broken wire, disconnected connector)
Short to ground in heater circuit wiring
Blown fuse or failed relay in heater supply circuit
Corroded, damaged, or water‑intruded sensor connector
Faulty NOx sensor heater element (internally open or high resistance)
PCM/ECM driver fault or internal short

Symptoms

Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
Stored P23B2 code and possibly related NOx/aftertreatment codes
Aftertreatment system warnings (SCR/DEF) or failed emissions test
Reduced ability of NOx sensor to heat up — delayed/failed sensor operation
Possible decreased fuel economy or restricted regeneration events on diesel systems (depending on vehicle)
No obvious change in driveability in many cases until other systems are affected

What to check

Read and record all related codes with a capable scan tool (live data and freeze frame)
Visual inspection: harness, connector, clips, and seals for Bank 1 Sensor 3 — look for corrosion, water ingress, damaged insulation, or pin damage
Check fuses and relays related to NOx/heater power supply
Backprobe the sensor connector with connector connected (ignition on) and measure supply voltage and PCM driver output
Measure heater resistance at the sensor with connector disconnected (compare to specification)
Wiggle test wiring while monitoring voltage/current to reproduce intermittent faults

Signal parameters

Typical heater supply voltage: ~12 V (battery voltage) with ignition ON or when heater request active
PCM driver: low-side switch/pulse-width modulated (0 V to battery) — control duty varies by manufacturer
Expected heater resistance (cold): commonly in the range ~5–50 ohms (consult vehicle service data for exact spec)
Expected heater current when active: typically 0.1–3 A depending on heater design
Open-circuit condition: infinite/OL resistance at heater pins; short-to-ground: near 0 ohms between heater supply and ground (verify per vehicle)
When heater is commanded ON, supply should present battery voltage and driver should switch to ground allowing current flow

Diagnostic algorithm

Retrieve freeze frame and all active/pending codes; check for related aftertreatment codes (NOx, SCR, DEF).
Perform a visual inspection of Bank 1 Sensor 3 harness and connector for damage, corrosion, or contamination. Repair connector damage and clean terminals as needed.
Verify fuses/relays for NOx heater power. Replace any blown fuses or faulty relays and retest.
With ignition ON (engine off), backprobe the sensor connector: verify presence of battery voltage on the heater supply pin(s). If supply is missing, trace supply fuse/relay and wiring to power source.
Command the heater ON using a scan tool (if available) and observe the PCM driver output. Measure voltage/current while commanding to determine if driver is switching and supplying current. Note any PWM behaviour.
Disconnect sensor and measure heater resistance with a multimeter. Compare to factory spec. Open or very high resistance indicates failed heater element; very low resistance indicates short.
If supply and ground are good but heater resistance is out of specification, replace the NOx sensor. Re-scan and clear codes, then perform a test drive/regeneration as required.
If heater element checks good but circuit still reports low, inspect wiring continuity between PCM and sensor connector for opens or shorts to ground/power and repair any damaged wiring.
If wiring and sensor are good and heater driver does not operate correctly when commanded, suspect PCM driver failure—verify with manufacturer procedures before replacing PCM.
After repairs, clear codes, perform necessary relearn/tests and re-check system for return of fault.
Note: follow vehicle manufacturer safety and diagnostic procedures; avoid replacing PCM without confirming wiring and sensor failures.

Likely causes

Open or high‑resistance connection between PCM and sensor (broken wire or poor connector)
Failed heater element inside NOx sensor (open/high resistance)
Blown fuse or failed heater power supply relay
Corroded/contaminated connector causing high resistance

Fault status

⚠️ Status

NOx sensor heater circuit voltage/operation below threshold for Bank 1 Sensor 3. PCM detected insufficient heater current or unexpected low voltage indicating possible open/high resistance or short in heater circuit.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours