General System Description
Transmission Controls:The automatic transmission is controlled electronically and hydraulically.
The Transmission Control Module (TCM) -J217- for the automatic transmission obtains information from components that have an effect on the shifting. Based on this information the TCM controls the respective solenoid valves in the valve body. The solenoid valves direct the oil pressure created by the ATF oil pump to the respective clutches or brakes.
Malfunction Recognition By The TCM:
The TCM is equipped with Diagnostic Trouble Code (DTC) memory. Malfunctions that occur in the monitored sensors, components, or wiring are stored in DTC memory, which can be checked using the VAG 1551 or VAG 1552 Scan Tool (ST). If the printer of the VAG 1551 scan tool is switched on, the DTCs will be printed. Refer to "Diagnostic Trouble Code Charts" at "On-Board Diagnostics (OBD) II With VAG 1551". Testing and Inspection
The On Board Diagnostic (OBD) system differentiates between "static" and "sporadic" malfunctions. Static malfunctions are stored until DTC memory is checked and then erased using the VAG 1551 scan tool. If a malfunction that has been stored as "static" no longer exists after the ignition is switched on, it will be converted to "sporadic."
Malfunctions that occur sporadically are identified by the "/SP" designation in the VAG 1551 scan tool display. A sporadic malfunction is automatically erased after 40 engine cold-starts (and subsequent transmission warm-up cycles). A warm-up cycle is recognized when the ATF temperature is below 71°C at start and rises to at least 21°C.
The OBD program can be initiated using the VAG 1551 scan tool in "Rapid data transfer" operating mode 1.
A list of OBD functions accessible using the VAG 1551 scan tool is provided at "On-Board Diagnostics (OBD) II Functions". Testing and Inspection
TCM Backup Functions:
If one or more components or sensors malfunction, the TCM -J217- activates corresponding substitute functions or backup programs. This ensures that the automatic transmission operates without damage or effect to the operation or quality of the shifting.
If certain malfunctions occur and the TCM is active, the transmission range engaged at that moment is maintained. As soon as the driving situation permits, the TCM activates the "mechanical backup with active control module" mode while ensuring transmission security.
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 of the segments of the transmission range selector lever display are lit up completely.
- The Malfunction Indicator Lamp (MIL) is switched on after 3 Dcy.
- Check DTC memory and consult DTC table.
If the TCM malfunctions (e.g. there is a power loss or a connector is disconnected) the transmission immediately operates in "mechanical backup with non-active control module" mode.
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 of the transmission range selector lever display are dark.
- The Transmission Control Module (TCM) -J217- is completely inoperative, i.e. it cannot conduct its OBD program.
- The Malfunction Indicator Lamp (MIL) is switched on when the Engine Control Module (ECM) recognizes the CAN-Bus malfunction (missing data exchange between the ECM and TCM) after 2 Dcy.
- If necessary, check DTC memory of ECM.