DEF Dosing Valve Stuck Closed

What this code means

The DEF injection valve (dosing valve) that sprays DEF into the exhaust is stuck in the closed position. No DEF is being injected.

Symptoms

• DEF not being consumed (level not dropping)
• NOx emissions elevated
• SCR efficiency code may follow
• Derate warning countdown
• Check Engine Light
• Potential speed limitation

Common causes

• DEF crystallization blocking valve
• Dosing valve solenoid failure
• DEF frozen in valve (cold weather)
• Contaminated DEF clogging valve
• Valve mechanical failure

Diagnostic steps

1. Monitor DEF dosing command vs actual injection
2. Inspect dosing valve for crystallization
3. Test valve solenoid electrically
4. Check DEF line heating system
5. Attempt to command valve open with scan tool

Repair notes

Replace DEF dosing valve. Clean DEF supply line. Check DEF line heater operation for cold weather crystallization prevention.

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