P21BCCold Start Cylinder 7 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
- From cylinder 7 on, the code is limited to engines with at least seven cylinders – in practice V8, V10, V12 and W12. Common petrol V8 with direct injection are GM's 5.3- and 6.2-litre small blocks, which a GM bulletin describes with dual-pulse injection after a cold start, and Ford's 5.0-litre Coyote, which since 2018 combines port and direct injection. P21BC reports that during the cold-start heating phase the injection timing of cylinder 7 missed its target; on dual-system engines the direct injector is the part whose timing is shifted. No manufacturer publishes use of P21BC. If the code repeats on cylinder 7 only, test that injector cold and compare it with the others. Related: P021A (warm), P2B0E (cold-start pulse), P0207, P0307.
- What you may notice
- Check engine light after cold starts
- Rough cold idle, sometimes with P050D or a cylinder 7 misfire code
- Likely causes
- LikelyDirect injector of cylinder 7 slow to open or leaking at low temperature
- PossibleChafed or heat-damaged wiring to injector 7
- RareFault in the high-voltage injector driver of the engine module
- 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: €120 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.