What it means
The NH3 sensor heater circuit signal is below the expected range. The code does not by itself identify the cause or the control module’s response.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The NH3 sensor heater warms the sensing element so it can measure ammonia in the exhaust. P24E7 sets when the control module detects the heater-circuit signal below its expected range; a grounded control wire, an internally shorted heater, or a driver fault can pull it low.
Common causes
Most likely first.
- Heater control wire shorted to ground
- Internal short across the heater element
- Low-side driver pulled down in the control module
Symptoms
- Check-engine light on
- Aftertreatment or emissions warning
- Reduced engine power
- Emissions inspection failure
How to diagnose it
- Record freeze-frame data and check heater-circuit live data and related codes to determine when the low condition occurs.
- Inspect the NH3 sensor heater wiring and connector for chafing, corrosion, or contact with ground.
- Use the wiring diagram and manufacturer's procedure to test the heater control wire for a short to ground.
- Test the heater element for a short or abnormal condition using the manufacturer's specification.
- If the sensor and wiring pass, check the control module's heater driver using the prescribed procedure.
Common fixes
- Clean and secure corroded heater-circuit connector terminals.
- Repair a heater control wire shorted to ground or chafed against the chassis.
- Replace the NH3 sensor if its heater element is shorted or fails specification.
- Repair the module driver only when tests confirm it is pulling the circuit low.
Can I keep driving?
The vehicle may be drivable, but an improperly heated NH3 sensor can impair emissions monitoring and may lead to an aftertreatment warning or reduced power. Avoid continuing if power is limited, and arrange diagnosis soon.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.