What it means
The NH3 sensor circuit signal is intermittent or erratic. The code does not establish the sensor location, expected signal shape, 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 monitors ammonia in the exhaust for the aftertreatment system. P24E5 means the control module has detected a signal that fluctuates or behaves unpredictably, rather than remaining consistently low or high; a loose connection, heat-affected wiring, or a drifting sensor element can cause this.
Common causes
Most likely first.
- Corroded or loose sensor connector
- Chafed or vibrating harness near the exhaust
- Aged ceramic sensor element drifting under heat cycles
Symptoms
- Check-engine light on
- Aftertreatment or emissions warning
- Reduced engine power
- Emissions inspection failure
How to diagnose it
- Save freeze-frame data and review NH3 sensor live data for dropouts or erratic changes, noting engine and exhaust temperature when they occur.
- Inspect the sensor connector for looseness or corrosion and check the exhaust-area harness for chafing, vibration damage, or heat damage.
- With the wiring diagram, check signal-wire continuity and look for intermittent opens or shorts while moving the harness gently.
- Check connector terminal tension and ground or supply connections as specified for the vehicle.
- If wiring remains stable, test the NH3 sensor across the conditions where the fault occurs using the manufacturer's procedure.
Common fixes
- Clean and secure a loose or corroded sensor connector.
- Repair and properly route a chafed or vibrating harness near the exhaust.
- Repair any intermittent open or short found in the sensor wiring.
- Replace the NH3 sensor if its signal remains erratic after circuit checks.
Can I keep driving?
You may be able to drive, but intermittent NH3 readings can impair emissions monitoring and may trigger reduced power or an aftertreatment warning. Limit unnecessary trips and arrange diagnosis, especially if power drops or warnings intensify.
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.