P2B12 is stored when injector 2's pulse offset has not been learned, so the controller still relies on a default value for the smallest injections. The public record contains no manufacturer using this exact code; the explanation here follows from the title and from the neighbouring monitors. Learning of this kind needs repeated coasting phases with fuel cut-off, because only then can the effect of a single test injection be picked up through the crankshaft speed signal, as a Bosch patent on zero-fuel quantity calibration sets out. Engines that rarely coast – long motorway runs, towing – or a recent adaption reset after injector work can therefore leave the learn unfinished. CARB treats feedback that never starts in time as a fault. Once learned but too far off, cylinder 2 reports P2B13 instead.
Medium severity. Can I keep driving?If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.
Cylinder 2 is numbered according to the manufacturer: check your engine's manual before working on it.
Symptoms
- Warning lamp without a clear driveability complaint
- Possibly louder combustion on cylinder 2 at low load
Most likely causes
- Driving profile without enough fuel cut-off phases (constant load, towing)
- Adaption values reset after work on injector 2 or the fuel system
- Crankshaft speed signal too noisy to detect the test injection
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P2B12 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- B: Subsystem depends on the code range
- 12: Specific fault in that system
Frequently asked questions
Can I keep driving with code P2B12?
If the car is running normally, drive in moderation to a repair shop. If it loses power or another warning appears, do not continue.
What causes code P2B12?
The most common causes are: driving profile without enough fuel cut-off phases (constant load, towing); adaption values reset after work on injector 2 or the fuel system; crankshaft speed signal too noisy to detect the test injection.
Related codes
- P2B13Cylinder 2 Injection Pulse Offset Exceeded Learning Limit
- P2B10Cylinder 1 Injection Pulse Offset Not Learned
- P2B14Cylinder 3 Injection Pulse Offset Not Learned
- P02CECylinder 2 Fuel Injector A Offset Learning At Min Limit
- P02CFCylinder 2 Fuel Injector A Offset Learning At Max Limit
- P0266Cylinder 2 Contribution/Balance
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.