P24E6

Code

Generic P — Powertrain

NH3 Sensor Heater Circuit/Open

Brand: Generic

Type: P — Powertrain

Views: UK: 24 EN: 44 RU: 27

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Page language: EN

Causes

Open or shorted heater element inside the NH3/NOx sensor
Broken wiring or connector (open circuit) between sensor and ECM
Corroded or loose connector terminals
Blown fuse or failed heater relay/power supply
Faulty ground at the heater circuit
ECM/PCM driver failure or software issue

Symptoms

MIL (Check Engine Light) illuminated
Reduced NOx aftertreatment performance or regen issues (on SCR systems)
Extended warm-up time before sensor responds
Possible reduced fuel/engine management performance if system is in limp mode
Related emissions fault codes stored

What to check

Read stored codes and freeze-frame data with a scan tool; note conditions when code set
Visual inspection of NH3 sensor, wiring harness, and connector for damage, corrosion, or disconnection
Confirm supply fuse(s) and heater relay (if equipped) are intact and functional
Backprobe the heater supply and ground with key ON and while commanding heater ON using a bi-directional scan tool
Measure heater resistance at the sensor (with harness disconnected) and compare to specification
Wiggle test wiring while monitoring live current/voltage for intermittent opens

Signal parameters

Heater supply voltage: battery voltage (~11–14.5 V) present at heater supply pin when ignition ON (or when relay/fuse supplies it)
Heater control: ECM typically switches the ground (low-side) to energize heater; expect to see switching to near 0 V when commanded ON
Heater resistance (typical): low-ohm range — commonly a few ohms up to ~20 Ω depending on sensor design (consult OEM spec). An open circuit (OL) indicates failed heater
Heater current draw: often in the ampere range when energized (example: 0.5–3 A). A very low or zero current indicates open/high-resistance circuit
When commanded OFF, heater circuit should show no switching/current draw

Diagnostic algorithm

Retrieve freeze-frame and live data. Confirm P24E6 is current or stored and note operating conditions.
Perform visual inspection of the NH3 sensor and harness. Look for heat damage, chafing, corrosion, or disconnected connectors.
Verify fuses and any heater relay. Replace faulty items and retest.
With ignition OFF, disconnect the sensor connector and measure heater element resistance across heater pins. Compare to OEM spec. An open or infinite reading indicates an internal heater failure.
With key ON (engine off) and using a DVOM or oscilloscope, check for battery voltage at the heater power feed pin. If no voltage, trace and repair power feed or relay/fuse.
Command the heater ON with a capable scan tool (bi-directional control) while backprobing the heater ground/driver pin. Verify the ECM switches the ground and measure current draw. No switching suggests ECM or driver fault.

Likely causes

Damaged sensor harness or disconnected connector at the sensor
Sensor heater element failed (internal open)
Blown fuse or failed heater supply relay
Poor ground or high-resistance ground connection to sensor heater
ECM heater driver fault (less common)

Fault status

⚠️ Status

Heater circuit open or high resistance detected on NH3 (NOx) sensor heater. ECM observed no/low current flow or open circuit condition and set code after diagnostic verification.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-3.0 hours