Q7 Quattro V8-4.2L (BAR) (2008)
Control Module: Testing and Inspection
CAN-Bus Terminal Resistance, TCM to ECM, Checking
CAN-Bus Terminal Resistance, TCM to ECM, Checking
The Engine Control Module (ECM) (J623) communicates with all databus capable control modules via a CAN databus.
These databus capable control modules are connected via two data bus wires which are twisted together (CAN_High and CAN_Low), and exchange
information (messages). Missing information on the databus is recognized as a malfunction and stored.
Trouble-free operation of the CAN-bus requires that it have a terminal resistance. The central terminal resistor is located in the Engine Control
Module (ECM) (J623).
Special tools, testers and auxiliary items required
‹› Multimeter.
‹› Wiring diagram.
Test requirement
‹› A CAN-Bus malfunction was recognized.
‹› The Engine Control Module (ECM) (J623) fuses OK.
‹› Battery voltage at least 12.5 V.
‹› Ignition switched off.
Test procedure
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Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] See: Powertrain Management/Computers and
Control Systems/Testing and Inspection/Scan Tool Testing and Procedures/Preliminary Check.
Start diagnosis
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Move the passenger seat to the rear upward position.
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Release retaining tabs - A, B, and C - and remove the right passenger seat trim.
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Move the passenger seat to the front upward position.
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Disconnect the Transmission Control Module (TCM) (J217) electrical harness connector - 3 -.