P21B9Cold Start Cylinder 4 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
- Four-cylinder petrol direct injection is the most widespread engine type this code can apply to, and cylinder 4 is its last cylinder. Ford's 2011 OBD summary for its first turbo direct-injection engine explains the background: during catalyst heating the injection timing may be specific to that mode, possibly as two injections with one during the compression stroke, which in turn needs a rail pressure window (checked as P053F). P21B9 reports that this cold-start timing went wrong on cylinder 4 alone. No manufacturer lists the code publicly, so the description rests on CARB's cold-start rules and the documented system codes. Warm-engine counterpart: P020D; electrical injector fault: P0204; cold-start pulse: P2B0B.
- What you may notice
- Check engine light, usually without drivability complaints
- Slightly longer catalyst warm-up and possibly higher cold-start emissions
- Occasional hesitation right after a cold start
- Likely causes
- LikelyDeposits on the tip of injector 4 changing its opening behaviour
- PossibleHarness fault on the injector 4 circuit
- RareRail pressure barely inside its window during cold start, affecting the last cylinder first
- 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 – €1,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.