P21BC: Cold Start Cylinder 7 Injection Timing

What it means

Cylinder 7 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

The engine control module calculates fuel injection timing for cylinder 7 during cold starting from crankshaft and camshaft position and operating data. This code sets when cylinder 7's cold-start injection timing falls outside its calibrated range; the code alone cannot distinguish injector, fuel-delivery, or timing-signal causes.

Common causes

Most likely first.

1. Cylinder 7 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 7 cold-start timing and misfire data during a cold start, noting coolant temperature and fuel pressure.
2. Inspect the cylinder 7 injector connector and harness for corrosion, loose pins, chafing, or heat damage.
3. Look for related injector, fuel-pressure, crankshaft, camshaft, or correlation codes that could indicate a shared fault.
4. Compare cylinder 7 injector correction or balance readings with the other cylinders under the same cold conditions.
5. Test cylinder 7 injector flow and control, then verify crankshaft and camshaft signals and mechanical timing if necessary.

Common fixes

• Repair a damaged or poorly connected cylinder 7 injector circuit.
• Correct a fuel-pressure or delivery issue confirmed by testing.
• Service or replace the cylinder 7 injector if testing finds abnormal flow or control.
• Repair a crankshaft or camshaft signal fault, or correct mechanical timing if it is verified as incorrect.

Can I keep driving?

Gentle, limited driving may be possible if the engine runs smoothly, but have the cold-start fault diagnosed promptly because misfire and smoke can increase emissions. Stop driving if the misfire is severe, the warning flashes, or the engine will not start reliably.