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Detroit Diesel SPN 4076 FMI 18 indicates a fault with the DEF dosing injector, which is the component responsible for spraying DEF fluid into the exhaust stream ahead of the SCR catalyst. When this injector fails or becomes restricted on DD13, DD15, and DD16 engines, the SCR system cannot properly reduce NOx emissions and a derate condition will follow.
Symptoms
- Check engine light on
- DEF or SCR warning light illuminated
- Engine derate condition
- White residue or crystallization around the injector
- Reduced engine performance
- SCR system unable to meet emissions thresholds
Cause
This code triggers when the ECM detects the DEF dosing injector is not performing within specification. Common causes include:
- Clogged or crystallized dosing injector from DEF deposits
- Failed or stuck dosing injector valve
- DEF injector electrical fault or wiring issue
- Restricted DEF supply to the injector
- Contaminated DEF causing injector blockage
- Failed return line preventing injector purge cycle
Can You Keep Driving?
Limited driving is possible but without a functioning dosing injector the SCR system cannot reduce NOx emissions. The ECM will trigger a progressive derate condition. This fault should be addressed promptly to avoid further damage to the aftertreatment system.
Recommended Action
Have the DEF dosing injector inspected for clogging, crystallization, or electrical faults. A clogged injector can sometimes be cleaned but is often more cost effective to replace. Also inspect the DEF return line to ensure the purge cycle is functioning correctly, as a blocked return line is a common contributing factor.
It means the DEF dosing injector is not operating correctly and the SCR system cannot properly inject DEF into the exhaust stream to reduce NOx emissions.
The most common causes are a clogged or crystallized DEF dosing injector, an electrical fault at the injector, or a blocked DEF return line preventing proper purging.
Short distances may be possible but the engine will derate without a functioning dosing injector. Address this fault as soon as possible.
Yes. The ECM will trigger a derate condition when the dosing injector cannot supply DEF to the SCR system at the required rate.
Inspect, clean, or replace the DEF dosing injector and verify the return line is clear. Once the injector is functioning correctly and the SCR system confirms proper DEF dosing, the code should clear.
Related codes
Need Immediate Help With This Fault Code?
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Important Notice
The information provided above is for general informational purposes only and should not replace official OEM service procedures. Always consult the manufacturer’s service manual or a qualified diesel technician before performing repairs. Operating a vehicle with active fault codes may result in further damage.