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With Manufacturer's Scan Tool



CAN-Bus, checking (through MY 1999)






1. Engine Control Module (ECM) -J248-
2. ABS Control Module
3. Transmission Control Module (TCM)
4. CAN-Bus

Function
The engine Engine Control Module (ECM) (item 1) communicates with the ABS Control Module (item 2) and the Transmission Control Module (TCM) (item 3) via a CAN-Bus (item 4).

At least two Control Modules capable of CAN-Bus are connected together via two CAN-Bus wires which are twisted together (CAN_High and CAN_Low) and they exchange information (messages). Missing information on the CAN-Bus will be recognized as a DTC by the Engine Control Module (ECM) as well as by other CAN-Bus Control Modules.

Two Control Modules have terminal resistors each of 120 ohms, these resistors ensure that the CAN-Bus can function without a malfunction. These terminal resistors are located in the engine and ABS Control Modules.

Special tools and equipment
- Test box VAG 1598/22
- Digital multimeter US 1119 (Fluke 83 or equivalent)
- Adapter kit VAG 1594
- Wiring diagram

Vehicles with manual transmission
- Test box VAG 1598/21

Vehicles with automatic transmission
- Test box VAG 1598/18

Test conditions
- DTC has been recognized by the CAN-Bus On Board Diagnostic.
- ABS Control Module coded to CAN-Bus operation

Test sequence

Vehicles with manual transmission
Vehicles with automatic transmission refer to the section below.

- Remove wiper arms and cowl panel.
- Release engine Engine Control Module (ECM) -J248- connector and remove.






- Connect test box VAG 1598/22 to Engine Control Module (ECM) -J248- wiring harness.
- Check CAN-Bus wiring with terminal resistor in ABS Control Module:
- Measure resistance between lest box sockets 68 + 75:

Specification: 115 to 135 ohms

If resistance value is within specified range refer to "If specification is obtained wires are not shorted" below.

If resistance is outside specified range:
- Remove air cleaner.






- Release ABS Control Module connector and remove.
- Check CAN-Bus wiring for short to one another:
- Measure resistance between test box sockets 68 + 75:

Specification: Infinite ohms

If specification is not obtained wires are shorted:
- Repair short in wiring using wiring diagram

- Check DTC memory, if necessary, repair any malfunctions.
- Erase DTC memory
- Display readiness code. If DTC memory has been erased or Engine Control Module (ECM) -J248- was disconnected readiness code must be reset. Testing and Inspection
If specification is obtained wires are not shorted:






- Connect test box VAG 1598/21 -1- to wiring harness for ABS Control Module -J104 -2-.
- Check CAN-Bus wiring between test box sockets 1598/22 and 1598/21 for open circuit using wiring diagram:
- 1598/22-1598/21
- Socket 68 and - socket 10
- Socket 75 and - socket 11
- Wire resistance: max. 1.5 ohms
- Also, check for shorts to battery positive (B+) or ground (GND).

If no wiring damage is found:
- Replace ABS Control Module.

If resistance is within specification:
- Remove air cleaner.






- Release ABS Control Module -J104- connector and remove.
- Check wiring between engine and ABS Control Module for short to ground and for short to positive (B+).

If no wiring damage is found:
- Reconnect Engine Control Module (ECM) -J248- connector.






- Connect test box VAG 1598/21 -1- to ABS Control Module wiring harness -2-.
- Check terminal resistor in Engine Control Module (ECM) -J248-:
- Measure resistance between test box sockets 10 + 11:

Specification: 115 to 135 ohms

If resistance is outside specification:
- Replace Engine Control Module (ECM) -J248-. Service and Repair

Vehicles with automatic transmission
- Remove wiper arms and cowl panel.






- Remove connector -arrow- from Transmission Control Module (TCM) -J217-.






- Connect test box VAG 1598/18 to Transmission Control Module (TCM) -J217- wiring harness -1- and lock connector -2-.
- Check CAN-Bus wiring with terminal resistors in Engine and ABS Control Modules.
- Measure resistance between test box sockets 3 + 25:

Specification: 55 to 75 ohms

If resistance is outside specification:
- Perform test per following table:






If resistance is within specification:
- Check wiring for short to battery positive (B+) or ground.
- Check DTC memory, if necessary, repair any malfunctions and erase DTC memory. Reading Diagnostic Trouble Codes
- Display readiness code. If DTC memory has been erased or Engine Control Module (ECM) -J248- was disconnected, reset readiness code. Testing and Inspection

If no wiring damage is found:
- Reconnect Transmission Control Module (TCM) -J248- connector.
- Switch on ignition.
- Erase DTC memory and road test.

Observe safety precautions when driving road test. See "Diesel Direct Injection System, Servicing". Service and Repair

- Recheck DTC memory for all Control Modules using the "automatic test sequence".

If a DTC on CAN-bus system in Engine Control Module (ECM) -J248- is still displayed after a test drive:
- Replace Transmission Control Module (TCM) -J217-.
- Check DTC memory, if necessary, repair malfunctions and erase DTC memory. Reading Diagnostic Trouble Codes
- Display readiness code. If DTC memory has been erased or Engine Control Module (ECM) -J248- was disconnected, reset readiness code. Testing and Inspection

Continuation for 115... 135 ohms
- Release Engine Control Module (ECM) connector and remove.
- Check CAN-Bus wiring with terminal resistor in ABS Engine Control Module (ECM) -J248-.
- Measure resistance between test box sockets 3 + 25:
Specification: 115...135 ohms

If resistance is outside specification:
- Check CAN-Bus wiring See below.

If wiring to ABS Control Module -J104- is OK:
- Replace ABS Control Module -J104-.
- Check DTC memory, if necessary, repair any malfunctions and erase DTC memory. Reading Diagnostic Trouble Codes
- Display readiness code. If DTC memory has been erased or Engine Control Module (ECM) -J248- was disconnected, reset readiness code. Testing and Inspection

If resistance is within specification:
- Reconnect Engine Control Module (ECM) connector.
- Remove air cleaner.






- Release ABS Control Module connector and remove.
- Check CAN-Bus wiring with terminal resistor in Engine Control Module (ECM) -J248-:
- Measure resistance between test box sockets 3 + 25:
Specification: 115...135 ohms

If resistance is not within specification:
- Check CAN-Bus wiring See below.

If no wiring damage is found:
- Replace Engine Control Module (ECM) -J248-. Service and Repair

CAN-Bus wiring, checking






- Release ABS Control Module connector and remove.
- Release Engine Control Module (ECM) -J248- connector and remove.
- Check CAN-Bus wiring for short to one another:
- Measure resistance between test box sockets 3 + 25, (test box 1598/18):
Specification: Infinite ohms

If specification is not obtained wiring is shorted:
- Repair wiring damage using wiring diagram:
- See Electrical Wiring Diagrams.
- Check DTC memory if necessary, repair any malfunctions and erase DTC memory. Reading Diagnostic Trouble Codes
- Display readiness code. If DTC memory has been erased or Engine Control Module (ECM) -J248- was disconnected, reset readiness code. Testing and Inspection

If specification is obtained wires are not shorted:






- Connect test box VAG 1598/22 to Engine Control Module (ECM) -J248- wiring harness.
- Check CAN-Bus wiring between test box sockets for open circuit using wiring diagram:
- 1598/22-1598/18
- Socket 68 and - socket 3
- Socket 75 and - socket 25
- Wire resistance: max. 1.5 ohms

- Also, check wiring for short to battery positive (B+) or ground.

If no wiring damage is found:






- Connect test box VAG 1598/21 -1- to ABS Control Module -2- wiring harness.
- Check CAN-Bus wiring between the test box sockets for open circuit using wiring diagram:
- 1598/22-1598/21
- Socket 68 and - socket 10
- Socket 75 and - socket 11
- Wire resistance: max. 1.5 ohms


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