Information Bus: Testing and Inspection
CAN-Bus, checking
CAN-Bus, checking (through m.y. 1999)
1 - Engine Control Module (ECM)
2 - ABS control module
3 - Transmission control module
4 - CAN-Bus
Function
The Engine Control Module (ECM) (item -1-)communicates with the ABS control module (item -2-) and the transmission control module (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 a twisted pair (CAN_High and CAN_Low) and exchange information (messages). Missing information on the CAN-Bus will be recognized as a malfunction by the ECM as well as by other CAN-Bus control modules.
Two control modules have 120 terminal resistors which make sure that the CAN-Bus can function without malfunctioning. These terminal resistors are located in the engine and ABS control modules.
Special tools and equipment
- VAG 1598/22 test box
- Multimeter (Fluke 83 or equivalent)
- VW1594 adapter set
- Wiring diagram
Vehicles with manual transmission
- VAG 1598/21 test box
Vehicles with automatic transmission
- VAG 1598/21 test box
Test conditions
- Malfunction has been recognized by CAN-Bus On Board Diagnostic (OBD)
- ABS control module coded to CAN-Bus operation
Test sequence
Vehicles with manual transmission
- Remove wiper arms and plenum chamber cover.
- Release Engine Control Module (ECM) harness connector and disconnect.
- Connect VAG 1598/22 test box to Engine Control Module (ECM) wiring harness.
- Check CAN-Bus wiring with terminal resistor in ABS control module.
- To do this, perform resistance measurement between test box sockets 29 + 41.
Specified value: 115-135 ohms
If the resistance value is within the specified range skip down
If the resistance value is outside the specified range:
- Remove air cleaner
- Release ABS control module harness connector and disconnect.
- Check CAN-Bus wiring for short to one another.
- To do this, again perform resistance measurement between test box sockets 29 + 41:
Specified value: infinite ohms
If the specified value is not obtained (wires have short to one another).
- Repair malfunction in wiring according to wiring diagram
- Check DTC memory. If necessary, repair any malfunctions and erase DTC memory
Reading Diagnostic Trouble Codes
Clearing Diagnostic Trouble Codes
- Display readiness codeMonitors, Trips, Drive Cycles and Readiness Codes
If DTC memory has been erased or the Engine Control Module (ECM) was disconnected from permanent battery (B+) voltage, generate the readiness code again. Monitors, Trips, Drive Cycles and Readiness Codes
If the specified value is obtained (wires do not have a short to one another).
- Connect VAG 1598/21 test box -1- to wiring harness for ABS control module -2-.
- Check CAN-Bus wiring between test box sockets 1598/22 and 1598/21 for open circuit according to wiring diagram:
1598/22 1598/21
Socket 29 Socket 10
Socket 41 Socket 11
Wire resistance: 1.5 ohms
- Also, check wiring for short to battery positive (B+)/Ground (GND).
If no malfunction is found in the wiring:
- Replace ABS control module:
If the resistance value is within specified range:
- Remove air cleaner
- Release ABS control module harness connector and disconnect.
- Check wiring between engine and ABS control module for short to Ground (GND) and for short to positive.
If no malfunction is found in the wiring:
- Reconnect Engine Control Module (ECM) harness connector.
- Connect VAG 1598/21 test box -1- to ABS control module wiring harness -2-.
- Check terminal resistor in Engine Control Module (ECM).
- To do this, perform resistance measurement between test box sockets 10 + 11:
Specified value: 115-135 ohms
If the resistance value is outside the specified range:
- Replace Engine Control Module (ECM)
Vehicles with automatic transmission
- Remove wiper arms and plenum chamber cover.
- Disconnect harness connector (arrow) from transmission control module.
- Connect VAG 1598/18 test box to transmission control module wiring harness -1- and secure harness connector -2-.
- Check CAN-Bus wiring with terminal resistors in engine and ABS control modules.
- To do this, perform resistance measurement between test box sockets 3 + 25:
Specified value: 55-75 ohms
If resistance measurement is outside the specified range:
- Perform test as per following table:
If resistance value is within specified range:
- Also check wiring for short to battery positive (B+) or Ground (GND).
- Check DTC memory. If necessary, repair any malfunctions and erase DTC memory
Reading Diagnostic Trouble Codes
Clearing Diagnostic Trouble Codes
- Display readiness code Monitors, Trips, Drive Cycles and Readiness Codes
If DTC memory has been erased or the Engine Control Module (ECM) was disconnected from permanent battery (B+) voltage, generate the
readiness code again Monitors, Trips, Drive Cycles and Readiness Codes
If no malfunction is found in the wiring:
- Reconnect transmission control module harness connector.
- Turn on ignition.
- Erase DTC memory and carry out road test.
Observe the safety precautions when performing a road test
- Again check DTC memory of all control modules using "Automatic test sequence."
If a malfunction on CAN-Bus system in Engine Control Module (ECM) is still displayed after test drive:
- Replace transmission control module.
- Check DTC memory. If necessary, repair any malfunctions and erase DTC memory.
Reading Diagnostic Trouble Codes
Clearing Diagnostic Trouble Codes
- Display readiness code Monitors, Trips, Drive Cycles and Readiness Codes
If DTC memory has been erased or the Engine Control Module (ECM) was disconnected from battery (B+) voltage, generate the readiness code again Monitors, Trips, Drive Cycles and Readiness Codes
Continuation for 115-135 Ohms
- Release Engine Control Module (ECM) harness connector and disconnect.
- Check CAN-Bus wiring with terminal resistor in ABS control module.
- To do this, again perform resistance measurement between test box sockets 3 + 25
Specified value: 115-135 ohms
If the resistance value is outside the specified range:
- Check CAN-Bus wiring
If the wiring to ABS control module is OK:
- Replace ABS control module.
- Check DTC memory. If necessary, repair any malfunctions and erase DTC memory
Reading Diagnostic Trouble Codes
Clearing Diagnostic Trouble Codes
- Display readiness code Monitors, Trips, Drive Cycles and Readiness Codes
If DTC memory has been erased or the Engine Control Module (ECM) was disconnected from permanent battery (B+) voltage, generate the readiness code again Monitors, Trips, Drive Cycles and Readiness Codes
If the resistance value is within the specified range:
- Reconnect Engine Control Module (ECM) harness connector.
- Remove air cleaner
- Release ABS control module harness connector and disconnect.
- Check CAN-Bus wiring with terminal resistor in Engine Control Module (ECM).
- To do this, again perform resistance measurement between test box sockets 3 + 25:
Specified value: 115-135 ohms
If the resistance value is not within the specified range:
- Check CAN-Bus wiring
If no malfunction is found in wiring:
- Replace Engine Control Module (ECM)
Checking CAN-Bus wiring
- Release ABS control module harness connector and disconnect.
- Release Engine Control Module (ECM) harness connector and disconnect.
- Check CAN-Bus wiring for short to one another.
- Again perform resistance measurement between test box sockets 3 + 25.
Specified value: infinite ohms
If the specified value is not obtained (wires are shorted together):
- Repair wiring malfunction according to wiring diagram.
- Check DTC memory. If necessary, repair any malfunctions and erase DTC memory.
Reading Diagnostic Trouble Codes
Clearing Diagnostic Trouble Codes
- Display readiness code Monitors, Trips, Drive Cycles and Readiness Codes
If DTC memory has been erased or the Engine Control Module (ECM) was disconnected from permanent battery (B+) voltage, generate the readiness code again Monitors, Trips, Drive Cycles and Readiness Codes
If the specified value is obtained (wires not shorted together):
- Connect VAG 1598/22 test box to Engine Control Module (ECM) wiring harness.
- Check CAN-Bus wiring between test box sockets for open circuit according to wiring diagram:
1598/22 1598/18
Socket 29 Socket 3
Socket 41 Socket 25
Wire resistance: max. 1.5 ohms
- Check wiring for short to battery positive or Ground (GND).
If no malfunction is found in the wiring:
- Connect test box VAG 1598/21 -1- to ABS control module wiring harness connector -2-.
- Check CAN-Bus wiring between test box sockets 1598/22 and 1598/21 for open circuit according to wiring diagram:
1598/22 1598/21
Socket 29 Socket 10
Socket 41 Socket 11
Wire resistance: max. 1.5 ohms