This diagnostic trouble code (DTC) is a generic powertrain code.
Although generic, the specific repair steps may vary depending on the make and model of your vehicle.
The Engine Control Module (ECM) tests for misalignment between both camshafts on one bank of the engine & the crankshaft. The misalignment would be at an idler sprocket for either bank or at the crankshaft. Once the ECM learns the position of both camshafts on one bank of the engine, the ECM compares the learned values to a reference value. The ECM will set a DTC if both learned values for one bank of the engine are exceeding a calibrated threshold in the same direction.
You may also see this DTC in a vehicle that also has other related DTCs such as P0008, P0016, P0017, P0018 and P0019. Bank 2 refers to the side of the engine that doesn't contains cylinder #1. Most likely you will not see just this code, you will also have a P0008 code set at the same time.
Symptoms of a P0009 DTC may include:
MIL (Malfunction indicator lamp) illumination
Roughness while accelerating
Poor fuel economy
Decreased power Timing chain "noise"
Potential Causes of a P0009 code may include:
Stretched timing chain
Crankshaft reluctor wheel has moved and is no longer referenced to top dead centre (TDC)
Timing chain tensioner problem
Generally, diagnosing and fixing this DTC will involve inspecting the timing chains and tensioners for excessive wear or misalignment, and inspecting the crank wheel for proper positioning. Then replacing parts as required. As said earlier, there are known issues with some GM engines so there may be updated or revised replacement parts.
Please consult a factory service manual for more vehicle make & model specific troubleshooting steps.