U0039 OBD2 specifically refers to the camshaft (cam) timing. In this case, if the cam timing is over-retarded, the engine light will be illluminated and the code will be set.
With U0039 code so start with the basics like a fuel pressure and fuel volume test. Or, you can start on the electrical side by doing a voltage drop on both the power and ground connections for the fuel pump. Some shops are reporting corrosion on the fuel pump ground that reduces power and fuel pressure.
Remove the air filter box assembly so you can access the transmission range switch. Turn the key to the ON position, but do not start the vehicle. Move the shifter to the neutral position. Align the alignment holes between the switch and the shift lever. Insert a 5mm drill bit into the adjustment hole to verify the proper alignment for the neutral position.
The crankshaft sensor signals the fuel injection computer or the ignition control when the cylinders are firing. This causes the ignition coil to provide a spark and the injector to inject fuel into each cylinder at the right time.If either sensor isn't working correctly, the car will run rough and the engine will be less efficient. In later car models, the car's computer can usually keep the vehicle running, but the engine warning light on the dashboard goes on to warn the driver.