General Information
On Board Diagnostic (OBD), Function
The automatic transmission is controlled electro-hydraulically.
The term "On Board Diagnostic (OBD)" is specifically for the electronic/electric control.
The self study program No. 180 describes in detail the On Board Diagnostic (OBD) function of the automatic transmission -J217- control module.
Additional information
- Self-study program No. 180.
Safety functions of transmission control module
The control module receives information from components that effect selection of gears and passes the information on to solenoid valves that control the spool valves in the valve body.
In the "Dynamic shift program" the control module reacts to the current driving conditions (e.g. driving or descending hills, trailer towing) also the driver's style of driving (e.g. sporty driving style) and selects the shift points accordingly.
The control module is equipped with a DTC memory so that in the event of an electronic/electrical component failure or on open circuit the fault can be determined quickly. Fault are recognized by electrical signals and stored in the
DTC memory.
Transmission control module fault recognition
The control module recognizes faults during vehicle operation and stores them in a DTC memory. This information will remain available even if the system voltage fails. Transmission Control Systems
The control module distinguishes between faults present (permanent) and temporary faults (sporadic).
If a fault is no longer present after a certain period or a lengthy drive, it will be converted to a sporadic DTC.
A fault will also be converted to sporadic when the DTC memory is not erased after repairs.
Faults which are stored in the memory as sporadically occurring faults, will be displayed as "sporadic DTCs" when checked by the scan tool VAG 1551. In such cases "SP" appears on the right of the display. If the printer is switched on, the print-out will show "sporadic DTC" after the identification of the fault.
If the sporadic DTC does not occur again after a certain period of time or a lengthy drive, the fault in DTC memory will be erased.
Safety functions of transmission control module
If faults occur while driving the control module can activate a back-up function or an emergency running program. It can though affect the operation and smoothness of the gearshifts.
In emergency running with the control module functioning all segments in the selector lever position display in the dash panel will light up.
In emergency running with a malfunctioning control module there will be no display in the selector lever position display.
The transmission will operate in emergency running; until the fault is no longer recognized by the control module over a predetermined period of time.
Scan tool VAG 1551 or tester VAS 5051
The On Board Diagnostic (OBD) must be initiated at the commencement of fault finding. Electrical faults which influence the braking characteristics will be stored. They can only be checked with the scan tool VAG 1551.
Functions which the scan tool VAG 1551 can register or perform. Selectable Functions When Using VAG 1551/1552 or VAS 5051
Vehicles with data BUS
Comprehensive information on the "data BUS" is given in self study program No. 186.
Advantages:
- Rapid data transfer between the control modules
- Less wiring in vehicle
Hydraulic regulation
A differentiation is made between two types of transmissions:
- Transmission with hydraulic regulation -E17-, on which the transmission input speed sensor (inductive sensor) is secured to the underside of the valve body.
- Transmission with hydraulic regulation -E18/2-, on which the transmission input speed sensor (camshaft position sensor) is secured behind valve body at transmission housing.