SPN 5246 FMI 0
STOP
DEF inducement
The DEF system triggered the derate: road speed is about to be limited.
SPN 5246 FMI 0: The DEF system triggered the derate: road speed is about to be limited. Stop: this is a stop-now code. Park safely and do not keep driving until it is checked.
Electrical · SCR / DEF
What it means
SCR inducement reached its final level: the ECM applies a torque derate and then limits road speed to 5 mph. It almost always follows a DEF quality, level or dosing code that was not corrected in time.
Most likely causes
Earlier DEF quality or level code left uncorrected
Very likely
Diluted or contaminated DEF in the tank
Very likely
Failing DEF quality sensor
Likely
DEF doser plugged with crystals
Likely
Tests, cheapest and most decisive first
1. Measure DEF concentration with a refractometer
Expected result: 32.5% urea
Tool: Refractometer
2. Read active and inactive SCR codes and their order
Expected result: The root code preceding 5246 is identified
Tool: J1939 scanner
3. Inspect the DEF doser and nozzle
Expected result: Clean nozzle, even spray pattern
Read it off your own dash
Take one photo and DERATE tells you whether you can keep driving.
DERATEDERATE assists. It does not replace inspection by a qualified technician.