Transmission Control Systems: Testing and Inspection

Diagnosis of Automatic Transmission

Monitoring of the Electronic Transmission NAG1

Generally:
The electronic controlled automatic transmission is monitored for malfunctions via its control module (TCM). The information if malfunctions occurs is send to the engine control module ECM for a minimum time of 20 ms.

Implausible Gear or Transmission Clutch Slipping
The EGS identifies the shifted gear under steady state conditions by verifying the signals of two speed sensors inside the transmission. If the verification value is out of range or if the gear identification is implausible, the modulation pressure is set to its maximum pressure after the time 1 (400 ms). Malfunctioning is detected and the corresponding fault code is stored if one of the above described malfunctions is present after the time 2 (1 sec).

Internal Checks of the TCM

The following is checked in the TCM:
- inadmissible variant
- check of external/internal watchdog
- EEPROM
- RAM and ROM

The monitoring of this components is performed after initialization of the system, that means ignition key in "on" position. A malfunction is detected and the corresponding fault code is stored if one the above checks is implausible.

Voltage Supply of the Control Solenoid Valves
The solenoid valves are supplied with battery voltage. The difference between battery and solenoid voltage is monitored via the TCM. If the difference of the measured voltages exceeds the admissible threshold of 2 V for more than 100 ms a malfunction is detected and the corresponding fault code is stored.

Implausible Shift Lever Position
The shift lever is monitored for the plausibility of its position.

Transmission Speed Sensors
The transmission is equipped with two speed sensors, the first for the input speed n2 and the secOBD for the input speed n3.

The following parameters are monitored:
- sensor voltage supply

The voltage supply is adjusted via hardware to a constant 6 V. If the voltage is lower than 4.8 V or higher than 7.2 V for more than 500 ms a malfunction is detected and the corresponding fault code is stored.

- functional check of n2 and n3 speed sensors

The input speed sensor n2 is monitored above the engine speed threshold of 450 rpm and above vehicle wheel speed threshold of 250 rpm.

The input speed sensor n3 is monitored above the output speed threshold of 150 rpm and the transmission in 3rd or 4th gear under steady state conditions.

A malfunction is detected and the corresponding fault code stored if the signals are implausible or no signal is recorded via the TCM within 800 ms.

CAN-Communication with ESP System, Output Speed
The TCM is monitoring the left and right vehicle wheel speed sensor signals from the ESP-system via CAN for plausibility. If the CAN-communication and wheel speed signals are implausible for more than 300 ms a malfunction is detected and the corresponding fault code is stored.

Gear Comparison Repeatedly Negative
The identified gear is compared with the TCM-gear under steady state conditions. If the gears are repeatedly identified as different a malfunction is detected and the corresponding fault code is stored.

Converter Lockup Clutch
Under several driving conditions depending on engine speed, -load and gear the converter lockup clutch is engaged with a defined slipping rate to have a decoupling of the engine vibrations from the powertrain (for comfort reasons). During slipping operating conditions the TCM calculates every 20 ms with the parameters engine speed, turbine speed, engine torque (calculated) and converter characteristic the frictional power, which is generated in the converter lockup clutch. If the frictional power exceeds a specified threshold a counter is activated in 20 ms intervals, if the frictional power falls below the threshold, the counter counts backwards.

If the counter value reaches 7, a malfunctioning converter lockup clutch is detected and the corresponding fault code stored.

Solenoid Valve of the Converter Lockup Clutch
The solenoid valve of the converter lockup clutch is controlled within is minimum (5%) and maximum keying ratio (94%). A malfunction is detected and the corresponding fault code is stored if after a time of 160 ms one of the following occurs:
- short circuit of shift valve against ground
- short circuit of shift valve against battery voltage
- short circuit of power stage
- broken cable of shift valve
- broken cable of power stage

Control Solenoid Valves
The control solenoid valves are monitored against the following:
- short circuit of the valves against battery voltage
- internal short circuit of the valves
- short circuit of valves against ground
- broken cable of powerstages
- short circuit of powerstages
- broken cable of valves

The monitoring of the malfunctions is partely performed by measuring the gradient of the nominal voltage control. If the gradient is to high or if one of the above malfunctions occurs for more than 300 ms, malfunctioning is detected and the corresponding fault code is stored.

Transmission Control Module Inputs/Outputs: