P21B8: Cold Start Cylinder 3 Injection Timing

What it means

Cylinder 3 cold-start injection timing is outside the calibrated range. The code does not by itself identify the cause.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

During a cold start, the engine control module calculates when to inject fuel into cylinder 3 using crankshaft and camshaft position and other operating data. This code sets when cylinder 3's cold-start injection timing is outside the calibrated range; it can reflect injector flow or control, fuel delivery, or timing-signal problems.

Common causes

Most likely first.

1. Cylinder 3 injector wear or altered flow
2. Injector wiring or control fault
3. Fuel pressure or delivery problem
4. Crank or cam timing signal issue

Symptoms

• Check-engine light
• Rough running or misfire after a cold start
• Hard starting when the engine is cold
• Increased exhaust smoke

How to diagnose it

1. Record freeze-frame data and check cylinder 3 cold-start timing and misfire data on a cold start, including coolant temperature and fuel pressure.
2. Inspect the cylinder 3 injector connector and harness for corrosion, loose pins, chafing, or heat damage.
3. Look for related injector, fuel-pressure, crankshaft, camshaft, and correlation codes that may point to a shared cause.
4. Compare cylinder 3 injector correction or balance readings with the other cylinders under the same cold conditions.
5. Test cylinder 3 injector flow and control, then verify crank and cam signals and mechanical timing if the injector checks are inconclusive.

Common fixes

• Repair a damaged or loose cylinder 3 injector connector or harness.
• Correct a confirmed fuel-pressure or delivery problem.
• Service or replace the cylinder 3 injector if testing shows abnormal flow or control.
• Repair a faulty crankshaft or camshaft signal, or correct verified mechanical timing error.

Can I keep driving?

If the engine runs normally after warming up, keep trips short and gentle while arranging prompt diagnosis; cold-start misfire and smoke can increase emissions. Stop driving if the misfire is severe, the warning flashes, or the engine struggles to start.