P21B6
Cold Start Cylinder 1 Injection Timing
Cylinder 1 cold-start injection timing is outside the calibrated window. Diesel cold-start uses adapted injection timing per cylinder to limit white smoke and noise; deviation typically points at a worn injector or faulty crank/cam correlation.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Common causes
Ordered by how often each turns out to be the cause.
- Injector flow-rate agedCommon
- Crank/cam correlation offPossible
Parts involved
- Fuel Injector
- Crankshaft Position Sensor
- Camshaft Position Sensor
P21B6 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.