911 Carrera S Cabriolet (997) F6-3.8L (2007)
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:
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inadmissible variant
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check of external/internal watchdog
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EEPROM
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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:
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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.