DEF Dosing Valve Stuck Open

What this code means

The DEF dosing valve is stuck in the open position, causing excessive DEF injection into the exhaust.

Symptoms

• DEF consumption very high
• White exhaust smoke (DEF steam)
• Ammonia smell from exhaust
• DEF tank empties rapidly
• SCR system over-dosing
• Possible SCR catalyst damage from excess urea

Common causes

• Dosing valve stuck mechanically
• Solenoid energized continuously
• Control module error commanding open
• DEF pressure forcing valve open
• Valve return spring broken

Diagnostic steps

1. Monitor DEF dosing rate vs commanded
2. Check DEF consumption rate
3. Test valve solenoid de-energized state
4. Inspect valve for mechanical damage
5. Read dosing module fault codes

Repair notes

Replace DEF dosing valve. Inspect SCR catalyst for ammonia slip or urea deposit damage.

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