RS 4 Quattro Sedan V8-4.2L (BNS) (2007)
Information Bus: Testing and Inspection
CAN-Bus Terminal Resistance, Checking
Can-Bus Terminal Resistance, Checking
This procedure is used to diagnose the CAN-Bus terminal resistance of the Motronic Engine Control Module (ECM) ( J623) and the Engine Control
Module (ECM) 2 (J624).
Special tools, testers and auxiliary items required
‹› Multimeter.
‹› Wiring diagram.
Test requirement
‹› A CAN-Bus malfunction was recognized.
‹› Fuse (S102) 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 the Engine Control Module (ECM) 2 ( J624) and 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).
Checking internal resistance,Motronic Engine Control Module (ECM) (J623)
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Disconnect the Instrument Cluster Control Module ( J285) electrical harness connector.
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Disconnect the Engine Control Module (ECM) 2 ( J624) electrical harness connector.
‹› The Motronic Engine Control Module (ECM) (J623) must remain connected for the following step.
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Using a Multimeter, check the Instrument Cluster Control Module (J285) electrical harness connector terminals 12 to 13 for resistance.
Specified value: 60 to 72 ohms (at approx. 20° C)
If the specified value was not obtained:
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Check the wiring.
Checking internal resistance,Engine Control Module (ECM) 2 (J624)
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Disconnect the Instrument Cluster Control Module ( J285) electrical harness connector.
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Disconnect the Motronic Engine Control Module (ECM) (J623) electrical harness connector.