What it means
The NH3 sensor supply voltage is below the expected range. The code does not identify the cause or the circuit’s grounding arrangement.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The NH3 sensor relies on a supply voltage for its exhaust ammonia measurements. P24EB sets when the control module detects that supply below the expected range; a supply wire shorted to ground, a poor module ground, or resistance at a corroded connector can lower it.
Common causes
Most likely first.
- Supply line shorted to ground
- High-resistance ground at the SCR module
- Connector pins corroded - high contact resistance
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 the NH3 supply reading and related codes to see whether the low condition is continuous or load-related.
- Inspect the sensor and SCR module connectors for corrosion, loose terminals, or wiring damage.
- Use the wiring diagram to check the supply line for a short to ground and inspect its routing for chafing.
- Test the SCR module ground and connector voltage drop under the manufacturer's specified conditions.
- If the wiring and ground pass, check the module supply output and sensor load according to the manufacturer's procedure.
Common fixes
- Clean and secure corroded supply or ground terminals.
- Repair a supply wire shorted to ground or chafed against the chassis.
- Repair a high-resistance SCR module ground connection.
- Replace a failed module supply component only after output testing confirms the fault.
Can I keep driving?
The vehicle may be drivable, but low supply voltage can prevent reliable NH3 sensing and affect emissions control; an aftertreatment warning or reduced power may occur. Arrange repair soon and avoid extended driving if power becomes 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.