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SPN 3216 FMI 4Severity: WarningVolvo

SPN 3216 FMI 4: NOx sensor signal too low (inlet/upstream) – wiring or sensor failure

Quick Answer

NOx sensor signal too low (inlet/upstream) – wiring or sensor failure

Code
SPN 3216 FMI 4
Severity
Warning
Applies to
Volvo
Can I drive?
Driving suitability is not established by this code alone.

Common Symptoms

  • Aftertreatment light
  • May stack into inducement
  • Code returns soon after clearing

Likely Causes

  • Connector corrosion (salt + moisture)
  • Harness rub near frame/heat shield
  • NOx sensor failed

Common Fixes

  • Inspect connector pins for green crust / water
  • Repair rub-through and secure harness
  • Replace sensor only after wiring checks
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What does SPN 3216 FMI 4 mean?

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NOx sensor signal too low (inlet/upstream) – wiring or sensor failure

Images for SPN 3216 FMI 4 (location, common failures)

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NOx sensor (example photo)
Example NOx sensor. Connector condition and wiring are common failure points in winter.
Credit: Wikimedia Commons • License: CC BY 3.0
Only use images you own or that have a license allowing commercial reuse (example: CC BY). Attribution alone is not permission.

Detailed guide for SPN 3216 FMI 4

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This shows up constantly on highway trucks because the upstream NOx sensor lives in a miserable spot. If the connector is corroded, a brand-new sensor won’t save you.\n\nQuick win: unplug, inspect, clean, dry, and make sure pins actually grip.

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SPN 3251 FMI 4: DPF differential pressure voltage low – open circuit / short to ground
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Mechanic community notes for SPN 3216 FMI 4

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