P12B9 – Cylinder 4 Injection Timing Related

P12B9 Possible Symptoms

Engine Light ON (or Service Engine Soon Warning Light)

P12B9 Possible Causes

Contaminated or improper fuel quality,Worn base engine components or differences in cylinder compression,Faulty Fuel Injector,Fuel Injector harness is open or shorted,Fuel Injector circuit poor electrical connection

P12B9 Description

The Engine Control Module (ECM) has the ability to learn injector timing performance. With the engine at operating temperature and in closed throttle decel mode, the ECM will pulse each injector individually and measure the changes in rotational speed of the crankshaft using the input from the Crankshaft Position Sensor (CPS). The ECM will run this diagnostic under three different fuel rail pressures for each injector. The ECM will adjust the timing of fuel delivered by each injector to obtain the desired RPM increase. The ECM stores the injector timing value required to increase the crankshaft speed by the desired RPM. If the ECM cannot control an increase in RPM for a given injector the appropriate code will set for that injector.