Engine control unit
Checking data bus matching resistor
Function
The engine control unit communicates with other data bus-compatible control units.
The control units are connected via a twisted pair of data bus wires ("high" and "low") and exchange information (messages). Information missing from the data bus will be recognised as a fault by both the engine control unit and other data bus control units.
The data bus requires a matching resistor to function fault free. This central matching resistor is located in the engine control unit.
Note:
You can read out which control units are actively connected via data bus to the engine control unit in measured value blocks 125 and 126 .
Test conditions
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● A data bus fault has been recognised by the self-diagnosis.
Special tools, workshop equipment, testers, measuring instruments and auxiliary items required
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◆ Test box V.A.G 1598/31
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◆ Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
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◆ Adapter set V.A.G 1594
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◆ Current flow diagram
Test sequence
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‒ Switch off ignition.
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‒ Remove battery.
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‒ Unlock the engine control unit connector and pull it off.
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‒ Connect test box V.A.G 1598/31 to engine control unit. The control unit wiring harness is not connected by this action.
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‒ Check centralized matching resistor in engine control unit.
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‒ To do this, measure resistance between test box
Sockets 58 + 60 Specification: 60 ...72 ω
If the resistance measurement is outside the specified range:
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‒ Renew engine control unit .
If the resistance value is within the specified range:
=> Current flow diagrams, Electrical fault finding and Fitting locations binder
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