On-Board Diagnostic (OBD), Operation

On Board Diagnostic (OBD) system, operation
The automatic transmission controls are electronic/ hydraulic.
The Transmission Control Module (TCM) -J217- receives information from components which influence the shifts. Based on this information, the control module activates the applicable solenoid valves in the valve body. The solenoids route the fluid pressure generated by the ATF pump to the clutches or brakes to be closed.

Transmission Control Module (TCM) DTC recognition
The term On Board Diagnostic system refers to the electrical\electronic part of the controls.

The control module is equipped with a DTC memory so that in the event of the failure of an electrical/electronic component, or in the event of an open circuit, the cause of the fault can be determined quickly.

DTC's are recognized by means of electrical signals. If malfunctions occur in the sensors or components being monitored, they are stored in the DTC memory indicating the type and location of the DTC.

If a DTC is present, it is initially saved as a statistical DTC. If the DTC is no longer present, it first of all becomes a sporadic DTC (SP).

DTC's that are saved in the DTC memory as sporadically present are displayed as sporadically occurring DTC's during a DTC scan. SP appears on the right side of the display. With the printer switched on, sporadically occurring DTC's are printed out following the DTC scan.

DTC's that are saved in the DTC memory as sporadically occurring DTC's are automatically deleted after 40 engine cold starts (and subsequent transmission warm up).

The potential of the On Board Diagnostic system can only be fully realized by using the Vehicle Diagnosis, Measurement and Information System VAS 5051.

Functions which the VAS 5051 Vehicle Diagnosis, Measurement and Information system can detect, Table of Selectable Functions.

Safety functions of the Transmission Control Module (TCM)
In the event of a failure of individual or multiple components or sensors, the Transmission Control Module -J217- activates replacement functions or limp-home programs. This ensures non-destructive operation of the automatic transmission with the concomitant effect on the function and quality of the shifts.

If critical DTC's occur and with the Transmission Control Module (TCM) J217 activated, the gear currently engaged is initially held. As soon as the situation with respect to the transmission and vehicle safety permits, the Transmission Control Module -J217- activates Mechanical Limp Home with Active Control Module.

Mechanical Limp Home with Active Control Module
^ Transmission shifts out of all forward gears into the hydraulic 4th gear. Converter clutch is open. All solenoids have no power.
^ Maximum shift pressure on the powertrain elements.
^ Reverse gear can be engaged. Shift lock (in P and N) is active.





^ All segments of the gear selector display are fully illuminated.

In the event of a Transmission Control Module (TCM) -J217- failure (e.g. power supply failure or harness connector disconnected) the transmission immediately continues to operate in Mechanical Limp Home with NonActive Control Module.

Mechanical Limp Home with Non-Active Control Module
^ Transmission shifts out of all forward gears into the hydraulic 4th gear. Converter clutch is open. All solenoids have no power.
^ Maximum shift pressure on the powertrain elements.
^ Reverse gear can be engaged. Shift lock (in P and N) is active.





^ All segments of the gear selector display are dark.
^ The Transmission Control Module (TCM) -J217- is completely inoperative, which means that On Board Diagnostic (OBD) is not possible.