General System Description
TRANSMISSION CONTROLGear selection is made with the selector lever. It is linked directly to the valve body by cable. At the same time, a selector lever position signal is sent to the Transmission Control Module (TCM) via the Multi-function Switch mounted on the side of the transmission case.
The following positions can be mechanically selected:
Position - Function:
P = Park. Mechanically moves the parking pawl to engage the teeth of the parking lock gear and prevent the vehicle from rolling away.
R = Reverse. A reverse gear lock prevents shifting into reverse gear until the vehicle speed drops below approximately 2 mph.
N = Neutral. No gears engaged.
D = Drive. Automatic driving position for normal driving. Provides automatic shifting from 1st to 5th gear and 5th to 1st gear.
4 = Automatic shifting from 1st to 4th and 4th to 1st gear. The 5th gear is blocked.
3 = Automatic shifting from 1st to 3rd and 3rd to 1st. The 4th and 5th gears are blocked.
2 = Automatic shifting from 1st to 2nd and 2nd to 1st gear.The 3rd, 4th and 5th gears are blocked. Gear selection is made with the selector lever. It is linked directly to the valve body by cable. At the same time, a selector lever position signal is sent to the Transmission Control Module via the Multi-function Switch mounted on the side of the transmission case.
The following safety functions are also present:
- Automatic Shift Lock III.
- Protection from impermissible downshifts to prevent downshifting into driving ranges that are too low.
- Protection of the motor from over- revving institutes a substitute program or an emergency driving gear in the case of a fault.
O1V Transmission Control Modules are equipped with permanent fault memory. The input and output signals of the TCM are constantly monitored and checked for plausibility. If malfunctions occur, substitute programs are activated depending on the fault type, or the emergency running mode is switched on to permit further operation of the vehicle. Data Trouble Codes can be read out using the V.A.G 1551 or 1552.
Input/Output Components
In general, transmission operation and shift timing is determined by Transmission Control Module (TCM J217.) The TCM receives input signals from various sensors, makes evaluations for those signals and then sends output signals to actuator components.
Here is an overview of the inputs and output signals needed for transmission operation:
INPUT SIGNALS
1. Engine Control Module - The Engine Control Module supplies the Transmission Control Module (TCM) with three signals:
- Engine RPM from Engine Speed Sensor G28 - This signal is required for calculation of transmission shift points.
Substitute function: There is no substitute function for this signal. If an RPM signal is not received by the TCM, the transmission will go into mechanical Emergency Running Mode.
- Injector Opening Time Signal - The TCM uses this signal as a measurement of instantaneous engine torque to calculate shift points.
Substitute function: There is no substitute function for this signal.
- Throttle Position Sensor from TPS Sensor G69 - The TCM uses this signal to determine engine load when calculating shift points. The ECM also recognizes the speed at which the throttle valve is opened and closed.
Substitute function: If the signal from the TPS is not available, a fixed value is supplied by the ECM.
- Additional Signals - The ECM communicates with the TCM during shifting to retard ignition timing. This has a positive effect on gear shift smoothness and service life of the automatic transmission.
2. Torque Converter Speed Sensor G182
This sensor (located in the valve body) measures the speed of the torque converter turbine during shifting. If an indexed value is not met or is exceeded, pressure to the clutches is increased or decreased accordingly. In addition, the length of shift time is evaluated. If a deviation from the set point shift time occurs for several shifts, for example, due to changes in the friction value of the clutches, the clutch pressure level is raised or lowered. These measures help achieve shift comfort during the life of the transmission.
3. Transmission Vehicle Speed Sensor G38
This sensor informs the TCM of the output speed of the transmission. The signal is used for calculating upshifts as a function of road speed.
4. Kick Down Switch F8
The Kick Down Switch is integrated into the Bowden accelerator cable. It is used to detect situations when the accelerator pedal is pressed beyond the full-throttle point. It moves the shift points higher to permit rapid acceleration.
5. Brake Light Switch F
The Brake Light Switch signal is used to help calculate downshift points and release the selector lever lock. There is no substitute function.
6. Transmission Fluid Temperature Sensor G93
Located in the wiring harness for the shift solenoids in the transmission oil pan. This signal is used to increase or decrease the fluid pressure to the clutches during shifting. It will also initiate special shifting programs during warm-up to facilitate catalytic converter heating.
7. Multi-function Switch F125
The Multi-function Switch is located on the transmission case and is actuated directly by the selector lever by cable.
The Multi-function Switch has these functions:
- Transmits the position of the selector lever to the TCM.
- Switches the back-up lights on.
- Disables the starter with driving position engaged and blocks the selector lever via the shift lock solenoid.
- Supplies current to the Cruise Control Switch.
If the Multi-function Switch F125 is detected as faulty, or if there is a faulty signal, the segments in Transmission Range Indicator G96 will light and the Emergency Running Mode will be initiated. Driving is only possible in D and R with reduced shift quality.
OUTPUT SIGNALS
8. A/C Control Head E87
The TCM reacts to a downshift input signal from the Kick-down Switch by switching the A/C compressor off to provide more power on acceleration.
9. Data Link Connector
The TCM provides serial data to the Data Link Connector for fault detection, output checks and measuring value blocks.
10. Valve Body/Solenoid Valves
The transmission Control Module actuates solenoid valves in the valve body to direct and regulate oil pressure to the appropriate clutches and plate brakes.
Solenoid Valves N88 - N91 - These valves control the application of the appropriate clutches and plate brakes. These valves are in either on or off.
Solenoid Valves N91 - N94 - These valves regulate pressure and apply various switching elements. As electronic pressure valves, they convert an electric control current into a proportional hydraulic pressure.
Solenoid valves N91 - N94 are not acoustically testable in the Output Check Diagnosis mode using the VAG 1551. Faults with these valves are stored in the permanent fault memory.
Faults detected in the circuits of Solenoid Valves N88 - N94 lead to activation of Emergency Driving Mode. If Solenoid N94 is faulty, the converter lock-up function is inoperative but all driving ranges can be engaged.
11. Engine Control Module (ECM)
The TCM sends signals to the ECM to provide information about transmission speed and shift timing. This will allow for retarding ignition timing during shifts.
12. Shift Lock Solenoid N110
Shift Lock Solenoid N110 prevents the gear selector lever from being moved from the Park and Neutral position. The TCM now sends a signal directly to the Shift Lock Solenoid N110. The solenoid is released when the brake pedal is pressed.
13. Transmission Range Indicator G96
The TCM sends a signal to the Transmission Range Indicator G96 to inform the driver which selector position has been chosen.
In addition, if a mechanical malfunction is detected by the TCM, it will light all the segments of the Transmission Range Indicator.
Additional Controls
There is no longer a Cruise Control System relay in the TCM. Voltage to the Cruise Control System is now supplied via the Multi-function Switch F125. The TCM supplies battery voltage to the system under the following condition:
- The selector lever is in the D, 4 or 3 position.
The control module for the shift lock system (J221) and the back-up light relay (J226) have been deleted.