P21B7Cold Start Cylinder 2 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
- P21B7 flags cylinder 2 during the cold-start phase only: the injection timing commanded for catalyst heating did not arrive as intended on that cylinder. The heating phase is brief and ends as coolant and catalyst warm up, so the monitor gets one chance per cold start and may need several cold starts before the code is confirmed. GM's 2025 diesel calibrations show the principle at system level: requested against scheduled start of injection, one sample per revolution, 88 failures out of 176 set P05EC with the lamp in the first trip. A cylinder-specific code like P21B7 appears in no public manufacturer document. If P020B (cylinder 2, warm) or P2B09 (cold-start pulse) are stored as well, the injector or its circuit is more likely than software.
- What you may notice
- Check engine light that appears only after cold starts
- Uneven running or slight smoke shortly after starting a cold engine
- Code may take several cold starts to return after clearing
- Likely causes
- LikelyInjector of cylinder 2 worn or coked, opening late at low temperature
- PossibleChafed or high-resistance wiring to injector 2
- RareWeak battery lowering injector supply voltage during and after cranking
- 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.