P21B8Cold Start Cylinder 3 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
- Cylinder 3 is the last cylinder of three-cylinder engines such as Ford's 1.0-litre EcoBoost, a turbo direct-injection unit. There a single cylinder accounts for a third of all combustion events, so a cold-start fault on it tends to be felt more than on larger engines. P21B8 reports that while the cold-start heating strategy was active, the injection timing of cylinder 3 left its tolerance. The code belongs to a per-cylinder series made necessary by CARB's demand to keep cold-start faults apart from warm-running faults; no manufacturer documents its use publicly. On engines with four or more cylinders P21B8 simply marks cylinder 3. Neighbouring checks: P020C for the warm engine, P2B0A for the cold-start injection pulse, P0303 for misfire.
- What you may notice
- Noticeable shaking at cold idle, especially on three-cylinder engines
- Check engine light after cold starts
- Normal running once warm
- Likely causes
- LikelyInjector of cylinder 3 with deposits or a weak coil
- PossibleMoisture or corrosion in the plug of injector 3
- RareEngine software update available for the cold-start calibration
- 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.