P24E9

Code

Generic P — Powertrain

NH3 Sensor Heater Circuit Performance

Brand: Generic

Type: P — Powertrain

Views: UK: 25 EN: 35 RU: 22

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MIL (check engine light) illuminated
Reduced or disabled SCR system performance messages (SCR derate)
Failed emissions inspection or increased NOx emissions
Possible limp-home strategy or reduced engine performance messages
No obvious engine running symptoms until aftertreatment reaches operating temperature

Read freeze frame and readiness status with a capable scan tool; record present conditions and occurrence strategy
Visual inspection of NH3 sensor, connector and wiring for damage, corrosion, contamination or overheating
Check fuses and relays related to NH3/heater circuit
Backprobe connector with heater commanded on to verify supply voltage and ground
Measure heater element resistance at the sensor (with sensor disconnected) and compare to specification
Check continuity between sensor connector and control module pins, and check for shorts to chassis ground or battery

Heater supply voltage: approximately battery voltage (~12 V) when commanded ON (may be PWM-modulated)
Heater current draw: typically under a few amps when operating; unusually high or zero current indicates fault
Heater resistance: low ohms range (single to low tens of ohms) when measured cold — compare to OEM spec
ECU reports: heater status flags, commanded duty cycle, measured current or temperature (if available)

Retrieve code, freeze-frame and any related DTCs (SCR, NOx or other sensor heater codes). Do not assume a final cause from one code. 2) Perform a thorough visual inspection of the NH3 sensor, harness and connector; look for corrosion, fluid ingress, heat damage and pin deformation. 3) Check relevant fuses and relays for continuity and proper operation. Replace if faulty. 4) With ignition ON (engine off) and using a scan tool, command the NH3 sensor heater ON. Backprobe the sensor connector: verify supply voltage (or PWM duty) and ground while commanded. 5) Measure heater resistance at the sensor with the sensor disconnected from the harness. Compare to OEM spec. An open or significantly out-of-spec resistance indicates a faulty sensor. 6) If supply/ground are not present or are abnormal, perform continuity and resistance checks between the sensor connector and the control module; check for shorts to ground or battery. Repair wiring or connector issues. 7) If wiring and supply are good but heater performance still wrong, verify module outputs and driver function. If module output is absent or incorrect and wiring is good, consider module fault or software issue. 8) After repair or replacement, clear codes, command heater on with scan tool and confirm proper voltage/current and that no new codes set. Road test as required and recheck readiness and monitor for reoccurrence.