P24EA: NH3 Sensor Supply Voltage Circuit

What it means

A fault is detected in the NH3 sensor supply voltage circuit. The code does not specify the supply voltage or the reason it is out of range.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The NH3 sensor needs a supply voltage to operate and report ammonia levels in the exhaust. P24EA indicates the control module has detected a fault in that supply circuit, without specifying whether the supply is open, shorted, or failing at its source.

Common causes

Most likely first.

1. Open or shorted supply wire
2. Failing supply rail inside the dosing module

Symptoms

• Check-engine light on
• Aftertreatment or emissions warning
• Reduced engine power
• Emissions inspection failure

How to diagnose it

1. Record freeze-frame data and check NH3 sensor and supply-circuit live data, along with related aftertreatment codes.
2. Inspect the sensor connector and supply harness for disconnection, corrosion, chafing, or pinching.
3. Use the wiring diagram to check the supply wire for an open or short, following the manufacturer's circuit test procedure.
4. Check the supply and ground connections under the specified test conditions for the vehicle.
5. If the wiring and sensor connections pass, test the dosing module's supply output against the manufacturer's specification.

Common fixes

• Reconnect and secure a loose NH3 sensor connector.
• Clean and repair corroded supply-circuit terminals.
• Repair an open, shorted, or damaged supply wire.
• Repair the module supply rail only after its output has been confirmed faulty.

Can I keep driving?

The vehicle may remain drivable, but the NH3 sensor may not operate correctly, impairing emissions monitoring and possibly prompting an aftertreatment warning or reduced power. Arrange diagnosis soon and avoid prolonged driving if power restrictions appear.