What it means
SCR NOx Catalyst Outlet Temperature Too High During Particulate Filter Regeneration: the component is overheating, typically from extended load or slip.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The SCR catalyst treats diesel exhaust to reduce nitrogen oxides, and its outlet temperature sensor monitors heat leaving the catalyst. This code sets when the outlet temperature exceeds its limit during particulate-filter regeneration, when exhaust temperatures are intentionally raised to clear soot.
Common causes
Most likely first.
- Excessive hydrocarbon dosing during regeneration
- Faulty exhaust temperature sensor or wiring
- Restricted exhaust flow increasing heat
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
How to diagnose it
- Capture freeze-frame data and confirm regeneration status, then check related particulate-filter, SCR, temperature-sensor, and dosing codes.
- Compare live outlet temperature with the SCR inlet and other exhaust sensors during regeneration to distinguish real overheating from an implausible reading.
- Inspect the outlet temperature sensor and harness for heat damage, poor connections, corrosion, or contamination.
- Review regeneration and hydrocarbon dosing data for signs that excessive fuel dosing or control behavior is creating too much heat.
- Check for exhaust restriction or flow problems and test the suspected cause to the manufacturer’s specification.
Common fixes
- Repair damaged outlet temperature sensor wiring or connector terminals.
- Replace the outlet temperature sensor if it fails the manufacturer’s checks.
- Correct excessive dosing or a faulty particulate-filter regeneration control condition.
- Repair a confirmed restriction in the exhaust path.
Can I keep driving?
Avoid sustained heavy-load driving while regeneration is overheating the exhaust, as the SCR catalyst can be damaged. Have persistent warnings or reduced power checked promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.