P24EE: NH3 Sensor Processor Performance

What it means

The control module detected a performance fault involving the NH3 sensor processor. The code does not specify a particular internal failure or control response.

At a glance

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

How it works

The NH3 sensor contains a processor that handles its measurements before the emissions control module uses them. The module monitors whether that processor performs as expected. P24EE sets when the NH3 sensor processor's performance is judged faulty, but the code alone does not identify a specific internal defect.

Common causes

Most likely first.

1. Internal processor or firmware fault
2. Brown-out from supply voltage dips
3. Module software outdated, reflash may resolve

Symptoms

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

How to diagnose it

1. Read all aftertreatment codes and freeze-frame data to check whether the fault coincided with a voltage drop, sensor fault, or other emissions event.
2. Inspect the NH3 sensor connector and wiring for corrosion, looseness, heat damage, or chafing that could interrupt power or communication.
3. Check the sensor's reported status and data on a scan tool for dropouts, implausible readings, or processor communication faults.
4. Check battery and charging-system operation and look for related supply-voltage codes that could indicate brown-outs.
5. Clear the code after addressing any supply or connection issue and see whether the NH3 sensor processor fault returns during the manufacturer's prescribed check.
6. If the wiring and power supply are sound, check for applicable control-module software updates and follow manufacturer tests to distinguish sensor processor failure from a module issue.

Common fixes

• Repair a loose, corroded, or damaged NH3 sensor power or communication connection.
• Resolve a battery or charging-system fault causing supply-voltage dips.
• Install an applicable module software update if it addresses NH3 sensor processor performance.
• Replace the NH3 sensor if manufacturer testing confirms its processor is faulty.
• Repair or replace the control module only if its own tests identify a module fault.

Can I keep driving?

If the vehicle drives normally, cautious short trips may be possible, but have the emissions fault checked promptly because warnings, reduced power, or inspection failure can follow. Treat any reductant countdown or power limitation as a reason to stop delaying repairs.