P202D: Reductant Leakage

What it means

A leak has been detected in the DEF (urea) supply system — usually by a pressure-decay test after pump shutdown, or by visible crystallisation around fittings.

At a glance

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

How it works

The reductant system stores and pumps DEF to the exhaust aftertreatment system. The control module checks whether pressure holds after the pump stops and may also detect DEF residue around the supply system. P202D sets when that check indicates DEF is escaping.

Common causes

Most likely first.

1. Cracked DEF line or fitting
2. Pump seal leaking
3. Injector mounting seal leaking

Symptoms

• Check engine light or NOx warning on
• AdBlue/DEF level or quality warning
• Possible no-start countdown after ignore period
• Failed emissions inspection (NOx)

How to diagnose it

1. Read the freeze-frame data and any reductant-system codes to see whether the fault followed a pump shutdown, a low DEF warning, or another system fault.
2. With the system cool and depressurized according to the vehicle's service information, inspect DEF lines, joints, the pump area, and the injector mounting area for wetness or dried white crystals.
3. Check the DEF level and inspect the fluid for contamination, since incorrect fluid or a low supply can complicate leak diagnosis.
4. Inspect the line and fitting connections for cracks, looseness, or damage, paying particular attention to areas showing DEF residue.
5. If no external leak is visible, use scan-tool pressure data or the manufacturer's pressure-decay test to determine whether the pump seal or a concealed connection is leaking.
6. After repairing any leak, clear the code and verify that the system holds pressure and no fresh DEF residue appears.

Common fixes

• Reseat or replace a leaking DEF line fitting.
• Replace a cracked or damaged DEF supply line.
• Replace a leaking reductant pump seal or pump assembly as specified by the manufacturer.
• Replace the injector mounting seal if DEF is escaping at the injector.

Can I keep driving?

A short trip may be possible if there is no visible spray or fluid loss, but arrange repair promptly and heed any DEF or NOx warnings. Continued leakage can disable emissions control and may lead to a no-start countdown.