P24EC: NH3 Sensor Supply Voltage Circuit High

What it means

The NH3 sensor supply voltage is above the expected range. The code does not establish a short to battery or a particular regulator failure.

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 regulated supply voltage to measure ammonia in the exhaust. P24EC means the control module detects that supply above the expected range; a short to battery voltage or a failed dosing-module regulator can cause the high reading.

Common causes

Most likely first.

1. Supply line shorted to battery voltage
2. Failed voltage regulator in the dosing module
3. 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

1. Save freeze-frame data and check the NH3 supply reading and related faults to confirm when the high condition occurs.
2. Inspect the supply harness and connectors for pinched wiring, corrosion, or contact with a battery-voltage source.
3. Use the wiring diagram and manufacturer's procedure to test the supply line for a short to battery voltage.
4. Check connector terminal condition and supply-circuit continuity, accounting for possible poor contact from corrosion.
5. If the wiring passes, test the dosing-module regulator output against the manufacturer's specification.

Common fixes

• Clean and secure corroded or loose supply-circuit terminals.
• Repair a pinched supply wire contacting battery voltage.
• Repair a supply line shorted to battery voltage.
• Repair the dosing-module regulator only after testing confirms its output is high.

Can I keep driving?

The vehicle may continue to run, but excessive supply voltage can disrupt NH3 sensing and emissions control, with warnings or reduced power possible. Arrange diagnosis promptly and avoid driving if electrical damage or worsening power restriction occurs.