P21B6Cold Start Cylinder 1 Injection Timing
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- After a cold start, petrol direct-injection and diesel engines deliberately move the moment of injection – for example with an extra late pulse – so that more heat reaches the catalyst. CARB 13 CCR 1968.2 (e)(11) wants every element of this strategy checked while it runs and reported apart from warm-engine faults. P21B6 pins such a deviation on cylinder 1. No manufacturer documents this code publicly; GM's 2025 diesel tables compare requested and scheduled start of injection on every cylinder but store only the system code P05EC. If cylinder 1 alone is flagged, a shared cause such as crank/cam synchronisation is unlikely; the injector, its wiring or its driver stage come first. Warm counterpart: P020A.
- What you may notice
- Check engine light after one or more cold starts
- Slightly rough idle in the first minute after a cold start
- No noticeable fault once the engine is warm
- Likely causes
- LikelyInjector of cylinder 1 responds late or inconsistently when cold
- PossibleCorroded or loose connector or harness at injector 1
- RareInjector driver stage in the engine control module faulty
- RareEngine module software with an overly strict cold-start check
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €80 – €1,200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.