S5 Quattro Coupe V8-4.2L (CAUA) (2009)
Engine Control Module: Testing and Inspection
CAN Bus Terminal Resistance, Checking
CAN-Bus Terminal Resistance, Checking
Special tools, testers and auxiliary items required
‹› Multimeter.
‹› Wiring diagram.
Test requirement
‹› A CAN-Bus malfunction was recognized.
‹› Motronic Engine Control Module (ECM) (J623) fuses OK.
‹› Battery voltage at least 12.5 volts.
‹› All electrical consumers such as, lights and rear window defroster, switched off.
‹› Vehicles with automatic transmission, shift selector lever into position " P" or "N".
‹› A/C switched off.
‹› Ground (GND) connections between engine/transmission/chassis OK.
‹› Ignition switched off.
Function
The Motronic Engine Control Module (ECM) (J623) communicates with other CAN-Bus capable control modules.
The control modules are connected by two data bus wires which are twisted together (CAN_High and CAN_Low), and exchange information
(messages). Missing information on the CAN-bus is recognized as a malfunction by the Motronic Engine Control Module (ECM) (J623) and the other
control modules connected to the CAN-bus.
Trouble-free operation of the CAN-Bus requires that it have a terminal resistance. This central terminal resistance is located in the Motronic Engine
Control Module (ECM) (J623).
Test procedure
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Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] See: Testing and Inspection/Scan Tool Testing
and Procedures/Preliminary Check.
Start diagnosis
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Disconnect the Data Bus On Board Diagnostic Interface (J533) electrical harness connector.
Checking internal resistance
‹› The Motronic Engine Control Module (ECM) (J623) must remain connected for the following step.
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Using a Multimeter, check the Data Bus On Board Diagnostic Interface (J533) electrical harness connector terminals 6 to 16 for resistance.
Specified value: 60 to 72 ohms (at approx. 20° C)
If the specified value was not obtained:
Checking wiring
If the manufacturers test box is being used, perform the following step.
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Install the test box.