Detailed guide for SPN 3363 FMI 18
Back to top ↑Winter finds weak DEF heater wiring fast. Check power and ground under load, not just with a lazy voltage check.
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Share ↓SPN 3363 FMI 18Severity: Warning
SPN 3363 FMI 18: DEF tank heater below normal – heater not heating / open circuit
Quick Answer
DEF tank heater below normal – heater not heating / open circuit
Code
SPN 3363 FMI 18
Severity
Warning
Applies to
Check OEM application
Can I drive?
Driving suitability is not established by this code alone.
Common Symptoms
- DEF warnings in cold weather
- Possible inducement if it persists
- DEF thawing slow
Likely Causes
- Open circuit wiring
- Bad heater element
- Connector corrosion
Common Fixes
- Check fuses/relays and power/ground
- Inspect harness routing and connectors
- Replace heater if it fails tests
Full technical sections↓
What does SPN 3363 FMI 18 mean?
Back to top ↑DEF tank heater below normal – heater not heating / open circuit
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