Detailed guide for SPN 4321 FMI 3
Back to top ↑High NOx catalyst inlet temps often occur when aftertreatment components are strained, like a clogged DPF or exhaust leak upstream.
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SPN 4321 FMI 3: Aftertreatment NOx catalyst inlet temp too high – catalyst stress
Quick Answer
Aftertreatment NOx catalyst inlet temp too high – catalyst stress
Code
SPN 4321 FMI 3
Severity
Warning
Applies to
Check OEM application
Can I drive?
Driving suitability is not established by this code alone.
Common Symptoms
- Aftertreatment light
- Occasional derate
- Temperature spike noticed
Likely Causes
- Exhaust leaks
- Clogged DPF increasing temps
- Catalyst overload
Common Fixes
- Inspect exhaust path
- Check DPF and DOC temperatures
- Repair leaks early
Full technical sections↓
What does SPN 4321 FMI 3 mean?
Back to top ↑Aftertreatment NOx catalyst inlet temp too high – catalyst stress
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