P2B12: Cylinder 2 Injection Pulse Offset Not Learned

What it means

The ECM has not yet learned the per-cylinder injection pulse offset for cylinder 2. Combustion equalisation between cylinders cannot be applied until adaptation completes.

At a glance

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

How it works

The ECM stores an individual injector pulse correction for cylinder 2 so it can balance that cylinder's combustion against the others. This code sets when the cylinder 2 correction has not been learned, often after the ECM loses its adaptation or an injector is replaced without the required learning procedure.

Common causes

Most likely first.

1. Adaptation lost after battery disconnect or ECM reset
2. Injector replaced without learn procedure

Symptoms

• Check-engine light
• Rough idle
• Slightly reduced engine performance

How to diagnose it

1. Check freeze-frame data and scan for other injector, misfire, or fuel-pressure codes before treating the missing cylinder 2 adaptation as an isolated fault.
2. Review service history for a recent battery disconnect, ECM reset, or cylinder 2 injector replacement.
3. Inspect the cylinder 2 injector connector and wiring for damage, corrosion, or a poor connection that could prevent reliable operation.
4. Use a scan tool to check whether the cylinder 2 offset is unlearned and whether the vehicle supports a prescribed injector learning procedure.
5. If the adaptation will not complete, test cylinder 2 injector operation and fuel pressure according to the manufacturer's procedure.

Common fixes

• Complete the manufacturer's injector adaptation procedure if the value was lost after a reset.
• Correct any poor connection or wiring fault at the cylinder 2 injector.
• Perform the required coding or learning procedure after cylinder 2 injector replacement.
• Repair a confirmed injector or fuel-pressure fault that prevents adaptation from completing.

Can I keep driving?

If the engine runs smoothly and the check-engine light is steady, short, gentle driving is generally reasonable while arranging diagnosis. Avoid heavy loads if it idles roughly or lacks power, since poor combustion can raise emissions and worsen running.