P21B6: Cold Start Cylinder 1 Injection Timing

What it means

Cylinder 1 cold-start injection timing is outside the calibrated range. The code does not by itself identify an injector or crank/cam fault.

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 coordinates fuel injection with crankshaft and camshaft position, using a separate timing calculation for cylinder 1 during cold starting. This code sets when cylinder 1's cold-start injection timing falls outside the calibrated range; it does not by itself prove that the injector or engine timing is at fault.

Common causes

Most likely first.

1. Injector flow-rate aged
2. Crank/cam correlation off

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 note the coolant temperature and starting conditions, then check cylinder 1 cold-start timing and misfire data during a cold start.
2. Inspect cylinder 1's injector connector and harness for loose pins, corrosion, chafing, or heat damage.
3. Check for related injector, fuel-pressure, crankshaft, camshaft, or correlation codes that could explain the timing deviation.
4. Compare cylinder 1 injector correction or balance data with the other cylinders under the same cold conditions.
5. If the fault remains, test cylinder 1 injector flow and verify crank-to-cam timing signals and mechanical correlation using the manufacturer's procedures.

Common fixes

• Repair a loose, corroded, or damaged cylinder 1 injector connection or wiring.
• Correct a fuel-delivery or pressure problem confirmed by testing.
• Replace or service the cylinder 1 injector if its flow or correction data is out of specification.
• Repair a crankshaft or camshaft signal fault, or correct mechanical timing if verification shows it is off.

Can I keep driving?

If the engine runs smoothly once warm and the warning is steady, limit driving and arrange diagnosis soon; cold-start misfire and smoke can increase emissions and may worsen. Stop driving if the misfire is severe, the warning flashes, or the engine will not start reliably.