SPN 4732 FMI 2 — DEF quality sensor — erratic readings
What it means: DEF quality sensor — erratic readings.
How serious / can you keep driving: Serious. Power derate likely — plan to stop soon.
Check first: Refractometer test — should read 32.5% urea
Don't risk it — look up listed providers near you and give them this SPN/FMI when you call.
Listed providers nearest Sparks, NV
Closest first. Tell them SPN 4732 FMI 2 and what the truck is doing. RoadService.app lists these providers and does not employ them or carry out the repair.
- 0.0 mi away — based in Sparks, NV · (775) 355-6884
- 0.0 mi away — based in Sparks, NV · (775) 356-7200
- 0.0 mi away — based in Sparks, NV · (775) 359-0550
Applies to: Navistar · Paccar · Sae · Volvo
What SPN 4732 FMI 2 means
DEF quality sensor — erratic readings.
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
DEF quality sensor — erratic readings.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Contaminated DEF (water. Other possibilities include fuel; washer fluid); Diluted DEF; Failed quality sensor; Contaminated/diluted DEF; Sensor.
Power derate likely — plan to stop soon. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Related codes
Codes that commonly appear alongside SPN 4732 FMI 2, or share the same subsystem.
- SCR Operator Inducement — Severe Derate Active (SPN 5246 FMI 0)
- Aftertreatment 1 Diesel Particulate Filter Differential Pressure - Data Valid But Above Normal Operating Range, Most Severe Level (DPF severely restricted / plugged) (SPN 3251 FMI 0)
- Aftertreatment 1 Diesel Exhaust Fluid Quality - Data Valid But Below Normal Operating Range, Most Severe Level (DEF quality/concentration incorrect) (SPN 4364 FMI 1)
- DPF Differential Pressure — Data Erratic (SPN 3251 FMI 2)
- DEF Dosing Unit — Not Responding Properly (SPN 3361 FMI 7)
- SCR Conversion Efficiency — Below Threshold (SPN 4364 FMI 18)
- DEF Quality — Out of Spec (SPN 4094 FMI 31)
- EGR Temperature — Too High (SPN 412 FMI 0)
Same symptom: DEF / SCR fault
Other codes in the DEF and SCR chain — the ones that end in an inducement countdown.
- Reductant System Performance Bank 1 (P204F) · Aftertreatment & Emissions
- Reductant Quality Deviation (P20EA) · Aftertreatment & Emissions
- DEF tank level low (SPN 1761 FMI 18) · Aftertreatment & Emissions
- DEF tank temp sensor — voltage high (SPN 3031 FMI 3) · Aftertreatment & Emissions
- Upstream NOx sensor — internal failure reported (SPN 3216 FMI 12) · Aftertreatment & Emissions
- SCR inlet NOx sensor — erratic (SPN 3216 FMI 2) · Aftertreatment & Emissions
Find a mechanic or related guides
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.