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SPN 4732 FMI 2 — DEF quality sensor — erratic readings
SeriousAftertreatmentPower derate likely — plan to stop soon
Applies to: Navistar · Paccar · Sae · Volvo
DEF quality sensor — erratic readings.
Don't risk it — get a diesel tech on the truck.
Look up listed providers near you and give them this SPN/FMI when you call.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Contaminated DEF (water
- fuel
- washer fluid)
- Diluted DEF
- Failed quality sensor
- Contaminated/diluted DEF
- Sensor
First moves (roadside)
- Refractometer test — should read 32.5% urea
- Drain and refill if contaminated
- Refractometer test
- Test DEF with refractometer (32.5% urea)
Common misdiagnoses
- Replacing the sensor when DEF is actually bad
- Replacing sensor without testing
- Replacing sensor without testing DEF
FAQ
What does SPN 4732 FMI 2 mean?
DEF quality sensor — erratic readings.
How serious is SPN 4732 FMI 2?
Serious — Power derate likely — plan to stop soon.
What's the most likely cause of SPN 4732 FMI 2?
The most common cause is: Contaminated DEF (water. Other possibilities include fuel; washer fluid); Diluted DEF; Failed quality sensor; Contaminated/diluted DEF; Sensor.
Can I keep driving with SPN 4732 FMI 2?
Power derate likely — plan to stop soon. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
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General diagnostic guidance for heavy-duty diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack). Not a substitute for a scan-tool diagnosis on your specific truck.