P246F
Reductant System Cold Start Performance
At cold start the SCR system is unable to begin reductant dosing within the required time. Typical cause on diesel cars in winter — frozen AdBlue in the tank or lines, failed tank heater, or a slow-warming SCR catalyst.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
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)
Common causes
Ordered by how often each turns out to be the cause.
- AdBlue frozen — tank or line heater not workingCommon
- SCR catalyst slow to reach light-offPossible
Parts involved
- Adblue Tank Heater
- Adblue Lines
- SCR Catalyst
P246F is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.