P21B7: Cold Start Cylinder 2 Injection Timing

What it means

Cylinder 2 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 injection timing for cylinder 2 during cold starting from crankshaft and camshaft signals and the engine's operating conditions. This code sets when cylinder 2's cold-start injection timing is outside its calibrated range, but it does not identify whether the injector, its control circuit, fuel delivery, or timing signals caused the deviation.

Common causes

Most likely first.

1. Cylinder 2 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. Save freeze-frame data and check cylinder 2 cold-start timing and misfire data during a cold start, noting coolant temperature and fuel pressure readings.
2. Inspect the cylinder 2 injector connector and wiring for damage, corrosion, loose pins, or poor contact.
3. Check for related injector-circuit, fuel-pressure, crankshaft, camshaft, or correlation codes before replacing parts.
4. Compare cylinder 2 injector correction or balance data with the other cylinders under the same cold conditions.
5. Test cylinder 2 injector operation and fuel delivery, then verify crank and cam signals or mechanical timing if those checks do not explain the fault.

Common fixes

• Repair damaged or poorly connected cylinder 2 injector wiring.
• Correct a fuel-pressure or delivery fault confirmed by testing.
• Service or replace the cylinder 2 injector if its flow or control is out of specification.
• Repair a crankshaft or camshaft signal fault, or correct verified mechanical timing error.

Can I keep driving?

Short, gentle trips may be possible if the engine runs normally, but arrange diagnosis promptly because cold-start misfire and smoke can raise emissions and may worsen. Avoid driving if the misfire is severe, the warning flashes, or starting becomes unreliable.