Every NH3 sensor leaves the factory with individual correction values for offset and gain stored in its own electronics. P24ED means this memory fails its integrity check, for instance a checksum mismatch or unreadable data, so the module cannot convert the raw probe signal into a trustworthy ammonia value. The fix is normally a new sensor; wiring rarely plays a part. It differs from the engine software choice in Ram bulletin 18-042-20, where 2014 Ram 3500 to 5500 cab chassis trucks receive one controller calibration with the ammonia sensor and another without it. No manufacturer documents P24ED publicly. CARB demands that heavy-duty sensors be checked for faults. P24EE covers the sensor processor.
Medium severity. Can I keep driving?It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.
Symptoms
- Check engine light on
- No valid ammonia value although wiring tests pass
Most likely causes
- Calibration data in the sensor module corrupted
- Power loss while the module was writing data
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P24ED means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 4: Emissions
- ED: Specific fault in that system
Frequently asked questions
Can I keep driving with code P24ED?
It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.
What causes code P24ED?
The most common causes are: calibration data in the sensor module corrupted; power loss while the module was writing data.
Related codes
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.