What it means
After cold start the AdBlue injection runs open-loop until SCR temperature is reached. The transition into closed-loop is taking longer than calibrated.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
After a cold start, the selective catalytic reduction (SCR) system initially controls AdBlue/DEF dosing without closed-loop feedback while the exhaust system warms. The module sets this code when the system takes longer than its calibration allows to reach the temperature and feedback conditions needed for closed-loop reductant control.
Common causes
Most likely first.
- SCR system warming up too slowly
- Low exhaust temperature from short or light-duty trips
- Faulty exhaust-temperature sensor or wiring
- SCR heater or temperature-control fault
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
How to diagnose it
- Read freeze-frame data and stored SCR or reductant codes to see the starting temperature, warm-up conditions, and when the transition delay occurred.
- Check AdBlue/DEF level and any quality or system warnings, since related faults can prevent normal dosing control.
- Compare exhaust-temperature sensor readings during a cold start and warm-up for implausible values or a reading that fails to rise.
- Inspect the relevant temperature-sensor wiring and connectors for damage, corrosion, or loose contacts.
- If sensor readings and wiring are sound, investigate slow SCR warm-up or a heater or temperature-control fault using the vehicle's diagnostic information.
Common fixes
- Repair a loose or damaged exhaust-temperature sensor connection.
- Replace a faulty exhaust-temperature sensor after confirming its reading is incorrect.
- Repair a temperature-control or SCR heater fault identified by diagnosis.
- Address related AdBlue/DEF supply or quality faults if they are preventing normal closed-loop control.
Can I keep driving?
A short drive may be possible, but heed any AdBlue/DEF warnings and do not ignore a no-start countdown; the vehicle may eventually refuse to restart. Avoid assuming repeated short trips will clear the fault, since continued delay can keep emissions control ineffective.
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.