P21BA: Cold Start Cylinder 5 Injection Timing

What it means

Cylinder 5 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 uses crankshaft and camshaft position data to time cylinder 5's fuel injection during a cold start. This code sets when that cylinder's cold-start injection timing falls outside the calibrated range; injector flow or control, fuel delivery, or timing signals may be involved.

Common causes

Most likely first.

1. Cylinder 5 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 5 cold-start timing and misfire data during a cold start, including coolant temperature and fuel pressure.
2. Inspect the cylinder 5 injector connector and harness for corrosion, loose pins, chafing, or heat damage.
3. Check for related injector-circuit, fuel-pressure, crankshaft, camshaft, or correlation codes before focusing on the injector alone.
4. Compare cylinder 5 injector correction or balance readings with those for the other cylinders under the same cold conditions.
5. Test cylinder 5 injector flow and control, then verify crankshaft and camshaft signals and mechanical timing if the cause remains unclear.

Common fixes

• Repair a damaged or loose cylinder 5 injector connection or wiring.
• Correct a fuel-pressure or delivery problem confirmed by testing.
• Service or replace the cylinder 5 injector if testing finds abnormal flow or control.
• 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 when warm, keep driving limited and gentle until the cause is found; cold-start misfire and smoke can increase emissions and may worsen. Stop driving if the misfire is severe, the warning flashes, or the engine becomes difficult to start.