General Information

On Board Diagnostic (OBD), Function
The automatic transmission is controlled electro-hydraulically.

The term "On Board Diagnostic" is specifically for the electronic/electric control.

The automatic control module -J217- receives information from components that effect selection of gears and passes the information on to solenoid valves that control the valves in the valve body.

The control module is equipped with a Diagnostic Trouble Code (DTC) memory so that in the event of an electronic/electrical component failure or on open circuit the malfunction can be determined quickly, malfunctions are recognized by electrical signals and stored in the DTC memory.

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

The automatic transmission control module sends signals into the data bus and uses signals from it. It exchanges signals (information) with other control modules.

Examples of signals from data bus (sent by engine control module)
- Accelerator pedal position (throttle valve position)
- Kickdown
- Engine speed
- Engine torque

Examples of signals into data bus (used by engine control module)
- Cruise control system
- Ignition timing influences

Not only the engine control module, but also other control modules exchange information via the databus - as in this example.

If the automatic transmission control module detects that signals are missing or faulty, the databus itself, another system or a component of another system may be defective.

Safety functions of transmission control module
The automatic control module -J217- receives information from components that effect selection of gears and passes the information on to solenoid valves that control the valves in the valve body.

Vehicles with diesel engines and stationary uncoupling
- 2.4 ltr. naturally aspirated diesel from 03.97
- 2-5 ltr. TDI from 09.98

To improve passenger comfort, the control module in these vehicles hydraulically selects neutral (stationery uncoupling of engine) when the selector lever is in the driving range "D" or "R", the vehicle is stationary (e.g. at a red light), the engine is idling and the brake is applied.

Transmission control module malfunction recognition
The control module is equipped with a DTC memory so that in the event of an electronic or electrical component failure or an open circuit, the malfunction can be determined quickly. Malfunction are recognized through electrical signals and stored in the DTC memory.

The control module recognizes malfunctions during vehicle operation and stores them in a DTC memory. VAG Codes

After analyzing the information the control module distinguishes between sporadic malfunctions and malfunctions present at this moment (static) and stores these.

If the malfunction is not present for a predetermined time or when driving over a longer distance, it is no longer recognized and becomes a sporadic malfunction.

Safety functions of transmission control module
If critical malfunctions occur when driving, the transmission will continue to operate in an emergency running mode. If the malfunction occurs in "D", "3" or "2", then 3rd gear emergency mode is activated.

If the malfunction occurs in "1", "P", "N" or "R" then the emergency running mode for that stage is activated.

If the engine is started again in the emergency running mode and the malfunction occurs when selector lever is in position "D", "3" or "2" then 3rd gear is activated hydraulically, until the malfunction is repaired.

For malfunctions which can lead to emergency running:
The transmission will remain in emergency running mode; until the malfunction is no longer recognized by the control module over a predetermined period.

Malfunctions which may lead to emergency running:
Open circuit in wiring, short-circuit, electrical or hydraulic components defective.

Wiring open circuit and/or data bus wiring short circuit.

Scan tool V.A.G 1551 and tester VAS 5051
Electrical malfunctions that affect vehicle performance can be determined with these devices.

Scan tool V.A.G 1551
- From July 1997 a further number on the right next to the Diagnostic Trouble Code (DTC) will be displayed/printed-out when checking the DTC memory (up-to-date program card version of V.A.G 1551). This number indicates the type of malfunction, which is also given again in words under the affected component.