997 Turbo, GT2 Camshaft Adjustment Failure, Fault Code P0021

One of the reasons that we love the Porsche 997 Turbo/GT2 so much is their Variable Turbine Geometry's reduced lag. This, coupled with Variable Valve Lift and Timing(on the intake cam, at least) help this engine deliver smooth and powerful performance throughout it's range of RPM. Let's take a closer look at why this is so badass.

Porsche's VarioCam Plus

VarioCam Plus is Porsche's unique way of utilizing your engine's oil pressure to activate an adjustment inside an variable camshaft sprocket to actively(while the engine is running) adjust camshaft timing(see the change in red below). Changes in valve lift occur when oil pressure is directed to affect the two-stage lifters. These lifters will lock and open the valves further with the help of special camshafts thus increasing output.

In this image, you can see the two-stage lifter highlighted in orange and blue- the center of the lifter operates the valves. In this position, the valve is being operated by the center camshaft lobe.

Here, we see that the lifter is in 'locked' position and the valve is now being operated by the outer, larger camshaft lobes. These lobes open the valves further and keep them open longer for increased performance.

Comparing the red shaded portion of this image with the image above. This illustrates the change taking place inside the variable camshaft sprocket. The center of this device drives the cam. The outer housing is driven by the chain. The performance difference takes place when the relationship between the chain drive and the camshaft changes.

These adjustments to cam timing and valve lift are activated by the DME(engine control unit) by way of solenoids that open, allowing pressurized oil flow into their given chambers. When this activation is interrupted for any reason, the DME registers a fault. 

Fault Code P0021

This fault occurs when camshaft timing activation is inhibited. There are several reasons that this fault could occur but the most common reason is blocked oil flow into the variable cam sprocket. When this happens, the camshafts must be removed and repaired/replaced in order for the fault code to clear.

Here, we have removed this turbo engine for this repair. The turbochargers, oil sump, headers and plumbing must all be removed to access the camshaft covers.

Here, the intake cam is removed. Note the two-stage lifters.

A sleeve that is pressed inside the camshaft rotates, causing the oil passage to be interrupted.

The holes in the cam/sleeve should line up perfectly. In this closeup image, you can see that they are not aligned. The fault occurs when this hole is completely blocked.

We correct the alignment of the sleeve and insert hollow pins to prevent future rotation.

This is a common issue on the 997 Turbo/GT2 engines. Luckily, no damage occurs during this failure. The repair can be performed quickly and the vehicle can be back on the road in a short period of time. Thank you for reading!!!