P24E2

Code

Generic P — Powertrain

NH3 Sensor Circuit Range/Performance

Brand: Generic

Type: P — Powertrain

Views: UK: 20 EN: 39 RU: 25

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Failed or degraded NH3 sensor (internal electronics out of spec)
Open, shorted, or corroded wiring or connector to the sensor
Sensor heater failure or heater circuit fault
Contamination of sensor by DEF, oil, coolant, or exhaust particulates
Poor ground or intermittent power supply to sensor
ECU/PCM software or internal control fault

Symptoms

Malfunction Indicator Lamp (MIL) illuminated
Reduced SCR performance, increased NOx emissions
Possible engine derate or limp-home strategy
Higher-than-normal DEF consumption or frequent dosing events
Failed emissions test or active regen abnormalities
Stored or pending related emissions codes (NOx, DEF heater)

What to check

Retrieve all stored and pending DTCs and freeze-frame data with scan tool
Compare live NH3 sensor values to upstream/downstream NOx sensors and expected ranges
Inspect sensor and harness for physical damage, corrosion, water/DEF contamination
Backprobe connector to verify sensor supply voltage and ground
Measure sensor heater resistance and heater supply activation with scan tool
Check battery voltage and charging system while testing sensor circuits

Signal parameters

Typical sensor analog output: 0–5.0 V (model-dependent); values outside expected band indicate fault
Some sensors provide a current output (0–20 mA) or differential voltage — consult OEM specs
Heater supply: nominal 12 V when commanded; heater resistance commonly tens of ohms (model-dependent)
Sensor warm-up time: tens of seconds to a few minutes; heater must reach operating temp
Signal response time/latency should be short (milliseconds); sluggish response suggests contamination or heater issue

Diagnostic algorithm

Connect a capable scan tool, read DTCs and freeze-frame data. Note conditions when fault set (engine temp, DEF level, exhaust temp).
Clear codes, run the engine to reproduce; monitor NH3 sensor, NOx sensors, SCR dosing, heater status and freeze frame.
Visually inspect sensor, connector and harness for damage, contamination, corrosion, bent pins or DEF crystallization. Repair as needed.
With key on/engine off, backprobe connector: verify proper reference/power (usually battery/ignition) and ground presence per OEM pinout.
Use multimeter to measure heater resistance and check heater supply is commanded and present when required; compare to spec.
Monitor live sensor output while operating and compare to upstream/downstream NOx sensors and expected behavior during warm-up and dosing events.
Wiggle-test harness while monitoring data to find intermittent faults. Check for high resistance/voltage drop under load.
If wiring/power/ground are good but signal out of range, substitute a known-good NH3 sensor (if available) or bench-test sensor per OEM procedure.
If replacement sensor cures fault, reinstall with correct torque/sealing and clear codes; confirm via drive cycle and verify SCR operation.
If fault persists after sensor and harness verified, consider ECU/PCM fault or software calibration — check for TSBs and perform reflash or replacement as directed.

Likely causes

Damaged sensor harness or connector (broken wire, pin corrosion)
High-resistance connection causing improper signal voltage
Heater element open or excessive resistance preventing sensor warm-up
Sensor contaminated by crystallized urea (DEF) or oils
Sensor failed out of calibration or age-related drift
Faulty ECM/PCM driver or signal processing

Fault status

⚠️ Status

NH3 Sensor Circuit Range/Performance — sensor output out of expected range or inconsistent with NOx/DEF values. MIL set; SCR dosing or emissions control may be impaired.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours