On Board Diagnostic (OBD)
On Board Diagnostic (OBD), function
The automatic transmission is controlled electro-hydraulically. On Board Diagnostic (OBD) refers specifically to the electronic/electric controls of the automatic transmission.
Transmission Control Module (TCM) -J217- with adaptive gear shift points (fuzzy logic)
The transmission control module determines the driving dependent gear shift points automatically.
Advantages:
- Gear shifts will be directed toward optimum fuel consumption
- Maximum engine output is always available
- Individual adaptation of gear shift points in all driving situations
- Gear shifts points are infinitely variable
Shift point variations for hills
An additional gear shift map automatically selects shifts for hills dependent upon accelerator pedal position and driving speed.
- Gear shift map for extreme uphill stretches is matched to engine output
- Gear shift map for extreme downhill stretches is matched to the braking effect of the engine
Safety functions of the Transmission Control Module (TCM) -J217-
The TCM -J217- receives information from components that effect the selection of gears and passes the information on to solenoid 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 malfunction or an open circuit the location can be determined quickly. Malfunctions are recognized by electrical signals and stored in the DTC memory.
If malfunctions occur in the monitored sensors or components, these are stored in the DTC memory together with an indication of the type of malfunction.
Malfunctions which only occur once are known as sporadic (temporary) malfunctions and are identified as such.
If malfunctions do not reoccur within a minimum of 5 km (3 miles) or 6 minutes or a maximum of 20 km (12 miles) or 24 minutes, they are stored as sporadic malfunctions.
Electrical malfunctions that affect vehicle performance can be determined with the VAG 1551 Scan Tool.
The diagnostic possibilities can only be fully exploited with operating mode 1, "Rapid data transfer of the VAG 1551 Scan Tool.
Emergency running mode
If critical malfunctions occur when driving, the transmission will continue to operate, but in an emergency running mode. If the malfunction occurs in "D","3" or "2" then 3rd gear emergency running mode is activated.
If the malfunction "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 the selector lever is in position "D", "3" or "2" then 3rd gear is activated hydraulically until the malfunction is corrected.
For all malfunctions which can lead to the emergency running mode, the transmission will remain in this 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 in wiring
- Wiring open circuit and/or CAN-Bus wiring short circuit.
- Electrical or hydraulic components faulty
TCM -J217- malfunction recognition
If a malfunction exists it is stored as a static malfunction. If the malfunction no longer exists after a predetermined period or distance travelled, it is considered a sporadic malfunction.
Sporadic malfunctions are stored in the memory and displayed as "sporadic" when retrieved by the VAG 1551 Scan Tool. "SP" appears on the right of the display in such cases. If the printer is switched ON, "sporadic malfunctions" are printed out after the DTC memory is addressed.
Malfunctions which are stored in the memory as sporadically occurring malfunctions are automatically erased after 1,000 km (625 miles) or 20 hours.
The information exchange between vehicle control modules is conducted by "CAN-Bus" The advantages of the "CAN-Bus" are a very rapid data transfer and less wiring in the vehicle.
Faulty CAN-Bus wiring, e.g. open circuits, can be directly detected as such by the control module. The exact location of the malfunction cannot be determined, however, until all control module DTC memories have been checked.
VAG 1551 Scan Tool
From July 1997 a further number on the right next to the DTC code will be displayed/printed-out when checking the DTC memory (with upto-date program card version of VAG 1551). This number indicates the type of malfunction, which is also given again in text under the affected component on the VAG 1551 display.
Memory
- Permanent memory yes
Data output
- Rapid data transfer yes
Data transfer between the control
modules via:
- CAN-Bus yes
Output Diagnostic Test Mode (DTM) no
Basic setting yes
Coding control module no
Reading measured value block yes