What it means
The NH3 sensor heater circuit does not perform as expected. The code does not establish a particular warm-up profile or control strategy.
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 cell so ammonia can be measured under the system's operating conditions. P24E9 indicates the control module sees heater performance outside its expected behavior, which can happen when an aged heater has increased resistance or transfers heat poorly to the sensing cell.
Common causes
Most likely first.
- Aged heater with increased resistance
- Poor thermal contact between heater and sensing cell
Symptoms
- Check-engine light on
- Aftertreatment or emissions warning
- Reduced engine power
- Emissions inspection failure
How to diagnose it
- Record freeze-frame data and review heater command, status, and NH3 sensor data to identify the conditions when performance falls short.
- Inspect the sensor installation and connector for looseness, contamination, corrosion, or damage that could affect heat transfer or circuit operation.
- Check heater wiring and connections for excessive resistance or intermittent contact using the manufacturer's procedure.
- Test heater operation and warm-up behavior against the manufacturer's specification under the conditions required by the service information.
- If wiring and installation are sound, evaluate the sensor heater and sensing cell as an assembly using the prescribed test.
Common fixes
- Restore a secure sensor installation if it is loose or poorly seated.
- Clean or repair poor heater-circuit connections.
- Repair any wiring resistance or intermittent fault found during testing.
- Replace the NH3 sensor if its heater no longer meets the manufacturer's performance specification.
Can I keep driving?
You may be able to drive, but the sensor may take too long to become reliable, reducing emissions monitoring and potentially triggering warnings or reduced power. Arrange diagnosis soon, particularly if the aftertreatment warning persists or power is limited.
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.