General Information
On Board Diagnostic (OBD), function
The automatic transmission is controlled electro-hydraulically.
The automatic Transmission Control Module (TMC) -J217- receives information from components that effect the selection of gears. It passes the information on to solenoid valves that control the solenoid valves in the valve body. The solenoid valves convey the fluid pressure generated by the ATF pump to the appropriate clutches and brakes to be engaged.
Transmission Control Module (TMC) -J217- malfunction recognition
The term "On Board Diagnostic (OBD)" applies specifically to the electronic/electric control.
The control module is equipped with a Diagnostic Trouble Code (DTC) memory so 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 together with an indication of the type of malfunction and malfunction location.
The control module recognizes malfunctions during vehicle operation and stores them in a DTC memory. This information will remain available even if the system voltage fails.
The control module distinguishes between permanent malfunctions that have occurred and sporadic malfunctions.
If a malfunction is no longer present after a certain time or a long drive, it will be converted to a sporadic (SP) DTC.
A malfunction will also be converted to sporadic when the DTC memory is not erased after repairs.
Malfunctions which are stored in the memory as sporadic malfunctions, will be displayed as "sporadic DTCs" when checked by the scan tool V.A.G 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 malfunction.
If the sporadic DTC does not occur again after 40 cold engine starts and subsequent transmission warm-up, the malfunction in DTC memory will be automatically erased.
The possibilities offered by On Board Diagnostic can only be used with the Vehicle Diagnostic, Testing and Information System VAS5051 or the V.A.G 1551 scan tool (mode 1, rapid data transfer).
Available functions of Vehicle Diagnostic, Testing and Information System VAS5051 or the V.A.G 1551 scan tool. Selectable Functions When Using VAG 1551/1552 or VAS 5051
Security functions of the Transmission Control Module (TCM)
When one or more components or sensors fail, the Transmission Control Module (TCM) -J217- activates the appropriate alternate functions or emergency programs. This ensures destruction-free operation of the automatic transmission with some effect on the function and quality of shifting.
When critical malfunctions occur with an active TCM, the current selected gear will be held. "Mechanical emergency running mode with the control module active" is activated by the TCM as soon as the driving situation regarding transmission security and engine security permits it.
Mechanical backup with active control module
- The transmission shifts out of all forward gears into hydraulic 4th gear. The torque converter clutch is unlocked (not applied). All solenoid valves are de-energized.
- Maximum shift pressure is applied to the power-transmitting elements.
- Reverse gear can be engaged. The shift lock solenoid is active (in "P" and "N").
- All segments of the transmission range selector lever display light up.
- The Multi-function Indicator Light (MIL) lights up after 2 driving cycles (Dcy); check DTC memory (compare with DTC table). Transmission Control Systems
If the TCM -J217- malfunctions (e.g. if the power supply is faulty or the connector becomes disconnected), the transmission will immediately switch to "mechanical back-up mode with inactive control module" and continue to operate.
Mechanical backup with non-active control module
- The transmission shifts out of all forward gears into hydraulic 4th gear. The torque converter clutch is unlocked (not applied). All solenoid valves are de-energized.
- Maximum shift pressure is applied to the power-transmitting elements.
- Reverse gear can be engaged. The shift lock solenoid is active (in "P" and "N").
- All of the segments transmission range selector lever display are dark.
- The MIL lights up when the Engine Control Module (ECM) has recognized a CAN-bus malfunction (missing data exchange between engine and transmission control modules) (after 2 Dcy); check DTC memory of the control module.
- Transmission Control Module (TCM) -J217- does not function at all, i.e. it cannot be checked via On Board Diagnostic (OBD).