The following adaptations/tests can be performed in this test module independently of one another:
In order to achieve the correct valve opening height, all the tolerances in the valve gear must be balanced by an adaptation. In this learning procedure, there is a slow approach to the mechanical adjustment limits of the eccentric shaft. The positions thus reached are stored and used in each operating point as the basis for calculating the current valve stroke.
The learning procedure runs automatically if, for example after a repair, a difference between the last stop position and the new starting position (with terminal 15 on) is detected. The adaptation can also be requested via the DIS-plus Tester.
After the learning procedure has been initiated via the DIS-plus Tester, a brief adjustment sound can be heard in the engine compartment. The DME reports whether the adaptation has run correctly or not.
For learning the stop position, faults can also appear in the fault code memory of the DME; there is a test module for this.
The irregular running measurement serves to detect irregular rotation of the individual cylinders. Here, the irregular running measurement is performed first on the smallest possible valve stroke. Then, the irregular running measurement is performed on the maximum possible valve stroke.
If the irregular running values of the individual cylinders vary strongly in the case of the smallest stroke, but do not deviate in the case of the largest stroke, the cause is unequal charging of the cylinders. Either the mechanics of the variable valve gear are worn or coking of the valves produces - with minimum opening - a difference in the air flow rate of the valves.
If the irregular running values of the cylinders vary both with minimum stroke and maximum stroke, the cause does not lie with the variable valve gear but elsewhere, for example the injection valves or ignition. Piston rings, hydraulic valve-clearance-adjustment elements, or strong coking can also be the cause. If there is cause for complaint, the compression test should also be performed as described below.
The compression test serves to detect variations in cylinder charge in the individual cylinders. Here, the compression test is performed first on the smallest possible valve stroke. Then, the compression test is performed on the maximum possible valve stroke.
If the compression values of the individual cylinders vary strongly in the case of the smallest stroke, but do not deviate in the case of the largest stroke, the cause is unequal charging of the cylinders. Either the mechanics of the variable valve gear are worn or coking of the valves produces - with minimum opening - a difference in the air flow rate of the valves.
If the compression values of the cylinders vary both with minimum stroke and maximum stroke, the cause does not lie with the variable valve gear but elsewhere, for example piston rings, hydraulic valve-clearance-adjustment elements or strong coking.
With this function, the engine is throttled, i.e. the throttle valve takes over regulation of the intake air volume. Independently of this, the variable valve gear is moved slowly from minimum to maximum stroke.
The slow adjustment enables diagnosis of sporadic sluggishness in the mechanics of the variable valve gear. For this reason, the adjustment is followed by a read-out of the fault code memory with reference to the corresponding test modules.
As a result of component and manufacturing tolerances, unfavourable conditions can lead to a slight deviation between the starting positions of the eccentric shafts of bank 1 and bank 2 of the Valvetronic.
That means that the calculated stroke of the intake valves is the same on both banks, but the actual stroke is different. This deviation, if correspondingly large, can lead to bumpy engine operation.
On the basis of characteristic variables, the DME can detect different strokes on both banks. Under certain external conditions, the eccentric shafts are adapted in such a way that the actual strokes on both banks are the same. This function is referred to as bank calibration. The bank calibration for the N62 engine can also be requested with the service function.