P22FF
- Powertrain
- Manufacturer-specific
- Emissions
Diagnose soon
Usually safe to drive short distances, but the fault will not clear itself and can worsen or fail an emissions test.
SCR NOx Catalyst Inlet Temperature Too Low
This code is in our catalogue but has not yet been through editorial review, so the guidance below is limited to what our structured data supports. We publish deeper diagnostic content only after a code has been reviewed — here is why.
The temperature sensor at the SCR catalyst inlet reports a value below the threshold needed for efficient ammonia conversion. Below roughly 180-200 °C the SCR cannot reduce NOx and reductant injection is suspended; if this is detected continuously the ECU sets the fault.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Usually safe to drive short distances, but the fault will not clear itself and can worsen or fail an emissions test.
- Urgency
- Diagnose soon
- Will it pass emissions
- No
- Check engine light
- Solid
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Temperature sensor drifts low or has shifted resistance | Very common | — |
| 2 | Short-trip operation - exhaust never reaches operating temperature | Common | — |
| 3 | Exhaust heater or heat-management strategy not active | Occasional | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
- SCR Inlet Temperature Sensor
- SCR Catalyst
- Exhaust Heat Management
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Awaiting review
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