Beetle L4-1781cc 1.8L Turbo (APH) (1999)
Engine Control Module: Testing and Inspection
CAN-Bus, Checking
With Manufacturer's Scan Tool
CAN-Bus, Checking
Function
The Engine Control Module (ECM) communicates with the ABS/ESP control module, instrument cluster, steering angle sensor and Transmission
Control Module (TCM) via a CAN-bus.
At least two data-bus capable control modules are connected and exchange information (messages) via two data-bus wires (CAN_High and CAN_Low)
that are twisted to each other. Missing information on the data-bus is recognized as a malfunction by the Engine Control Module (ECM) as well as by
other CAN- bus control modules.
The CAN bus requires a matching resistor of 120.0 Ohms to function properly. This matching resistor is located in the engine control module.
Special tools, test equipment and auxiliary items
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Test box V.A.G 1598/31
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Multimeter (Fluke 83 or equivalent)
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Adapter set V.A.G 1594
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Wiring diagram
Check conditions
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A malfunction has been recognized by the CAN bus On Board Diagnostic (OBD)
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ABS control module coded to CAN-bus operation
Test sequence
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Remove inner plenum chamber cover, left:
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Unlock the engine control module connector and pull it off.
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Connect test box V.A.G 1598/31 to engine control module. The control module wiring harness is not connected by this action.
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Check centralized matching resistor in engine control module.
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For this, perform a resistance measurement between test box sockets:
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Sockets 58 + 60 and
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Sockets 77 + 79:
Specification: 115 - 135 Ohms
If the resistance value is outside the specified range:
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Replace Engine Control Module (ECM)
If the resistance value is within the specified range:
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Disconnect test box VAG 1598/31 from engine control module.
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Connect test box VAG 1598/31 to control module wiring harness. Engine control module is not connected by this action
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Check CAN bus wiring for short to one another
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Remove the air cleaner.