J1939John DeereVerified

SPN 3361 FMI 5

Diesel Exhaust Fluid (DEF) Quality — Current Below Normal

intermediateEst. 60-120 minutes

This diagnostic information is provided for agricultural, off-road, and competition use. Repair procedures may not be appropriate for on-road emissions-controlled vehicles. Consult a certified technician for on-road repairs.

Overview

The aftertreatment control module has detected that the DEF quality sensor reading is below the acceptable threshold, indicating poor urea concentration in the DEF tank. This code frequently triggers during cold weather, after DEF refills from questionable sources, or when the DEF quality sensor itself has failed. May result in engine derate if not resolved within the allotted operating hours.

Symptoms

DEF warning lamp illuminated on dash

Engine power derate countdown active

Reduced maximum speed (5 MPH limp mode if ignored)

Diagnostic message on GreenStar or Gen 4 display

Possible DEF tank temperature warning

Regeneration inhibited

Common Causes

01Contaminated or diluted DEF fluid

02DEF stored beyond shelf life (12+ months)

03Faulty DEF quality sensor

04DEF crystallization in supply lines or injector

05Incorrect fluid in DEF tank (water, fuel, coolant contamination)

06Failed DEF pump module

07Software calibration mismatch after dealer update

Golden Values

Verified Measurements

The Examiner's Golden Values6 measurements

Parameter	Range	Typical	Notes
DEF Concentration Tool: DEF Refractometer	31.8–33.2 %	32.5 %	Urea concentration measured by quality sensor — API-certified DEF is 32.5%
DEF Temperature Tool: DEF Temperature Sensor Reading (Service Advisor)	15–86 °F	70 °F	Operating range — sensor will fault below 15°F
DEF Quality Sensor Voltage Tool: Multimeter	0.5–4.5 V	2.5 V	At sensor connector — proportional to urea concentration
DEF Pressure (Supply) Tool: Pressure Gauge or Service Advisor	60–90 PSI	75 PSI	In supply line between pump and injector — engine running, active dosing
DEF Injector Resistance Tool: Multimeter	6.5–8.5 Ω	7.5 Ω	Measured at injector connector — key off
Derate Timer Tool: Gen 4 Display or Service Advisor	0–10 hrs	—	Hours remaining before 5 MPH derate — check on GreenStar display

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