A8 Quattro Sedan V8-4.2L (AUX) (2001)
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Control Module: Description and Operation
TCM Backup Functions
If one or more components or sensors malfunction, the Transmission Control Module (TCM) -J217- activates corresponding substitute functions
or backup programs. This ensures that the automatic transmission operates without damage or effect to the operation or quality of the shifting.
If certain malfunctions occur and the TCM is active, the transmission range engaged at that moment is maintained. As soon as the driving situation
permits, the TCM activates the "mechanical backup with active control module" mode while ensuring transmission security.
Mechanical Backup With Active Control Module
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The transmission shifts out of all forward gears into hydraulic 4th gear. The torque converter clutch is unlocked (not applied). All solenoid
valves are de-energized.
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Maximum shift pressure is applied to the power-transmitting elements.
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Reverse gear can be engaged. The shift lock solenoid is active (in "P" and "N").
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All of the segments of the transmission range selector lever display are lit up completely.
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The Malfunction Indicator Lamp (MIL) is switched on after 3 Dcy.
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Check Diagnostic Trouble Code (DTC) memory and consult DTC table.
If the TCM malfunctions (e.g. there is a power loss or a connector is disconnected) the transmission immediately operates in 11 mechanical
backup with non-active control module" mode.
Mechanical Backup With Non-active Control Module
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The transmission shifts out of all forward gears into hydraulic 4th gear. The torque converter clutch is unlocked (not applied). All solenoid
valves are de-energized.
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Maximum shift pressure is applied to the power-transmitting elements.
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Reverse gear can be engaged. The shift lock solenoid is active (in "P" and "N").
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All of the segments of the transmission range selector lever display are dark.
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The Transmission Control Module (TCM) -J217- is completely inoperative, i.e. it cannot conduct its On Board Diagnostic (OBD) program.
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The Malfunction Indicator Lamp (MIL) is switched on when the Engine Control Module (ECM) recognizes the CAN-Bus malfunction
(missing data exchange between the ECM and TCM) after 2 driving cycles (Dcy).
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If necessary, check DTC memory of ECM refer to Powertrain Management.
