The continuously variable gearbox, marked with the code 722.8 (Autotronic system), is a solution used by Mercedes in 2004 and 2012 in the A-Class (W169) and B-Class (W245) models.
This design, based on a set of bevel gears and a transmission chain, does not have traditional gears, which ensures a smooth ride. The operation of the system is managed by an advanced mechatronic module. electro-hydraulic controller from Temic / Continental, immersed directly in the gearbox oil.
Real cause of failure: Filings and damage to the controller board
The diagnostic system most often indicates errors in the rotational speed sensors: Y3/9B3, Y3/9B4 and Y3/9B5. However, contrary to popular belief, the sensors themselves are rarely damaged.
The main culprit is the dirt inside the box. During operation (especially during infrequent oil changes), metal filings are formed. These magnetic particles settle on the sensors, creating a layer of sediment on them ("sticking" them).
A signal disturbed in this way or a change in electrical parameters causes an overload of the receiving systems on the motherboard. As a result, the electronic components on the controller board, which are responsible for interpreting the signal from the sensors, burn out or are damaged. It is the board's electronics, not the sensors themselves, that require specialized intervention.
Symptoms of damage to the CVT 722.8 controller
When components on the controller board are damaged by impaired reading from sensors, the driver observes the following symptoms:
- Transmission emergency mode — driving at limited speed.
- Message on the dashboard informing about a gearbox failure
- The engine warning light (MIL) or the "F" symbol comes on.
- Sudden jerk when engaging position "D" or "R".
- Complete inability to move.
- No communication with the box controller.
Professional repair of the Mercedes gearbox controller
Our company offers professional repair of the 722.8 and 722.7 controller. We do not replace unnecessarily functional sensors. we locate and replace damaged electronic components on the board that have failed due to the presence of filings. Thanks to this, we permanently remove the cause of errors Y3/9B3, Y3/9B4 and Y3/9B5, restoring full functionality of the controller.
Do you have a problem with the gearbox in your Mercedes? Trust electronics experts.
Call us and consult the possibility of repair
+48 796 160 103