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Engine Control Module: Testing and Inspection
CAN-Bus Terminal Resistance, Checking
CAN-Bus Terminal Resistance, Checking
Special tools, testers and auxiliary items required
- Multimeter.
- Wiring diagram.
Test requirement
- A CAN-Bus malfunction was recognized.
- The Engine Control Module (ECM) J623 fuses 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 Engine Control Module (ECM) J623 communicates with 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 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 Engine Control
Module (ECM) J623.
Test procedure
- Perform a preliminary check to verify the customers complaint. See: Powertrain Management/Computers and Control Systems/Testing and
Inspection/Initial Inspection and Diagnostic Overview/Preliminary Check
Start diagnosis
- Disconnect the Data Bus On Board Diagnostic Interface J533 electrical harness connector.
NOTE: The Engine Control Module (ECM) J623 must remain connected for the following step.
- Using a Multimeter, check the Data Bus On Board Diagnostic Interface J533 electrical harness connector terminals 6 to 19 for resistance.
Specified value: 60 to 72 ohms (at approx. 20 degrees C)
If the specified value was not obtained:
- Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).
- Check the wiring connection for damage, corrosion, lose or broken terminals.
- If necessary, repair the faulty wiring connection.
If no malfunction is found in the wiring:
- Replace the Engine Control Module (ECM) J623.
If the specified value was obtained:
Checking wiring
If the manufacturers test box is being used. Perform the following step.
- Install the Test Box 105 Pin VAG1598/42.
If the manufacturers test box is not being used. Perform the following step.
- Remove the Engine Control Module (ECM) J623.
- Using a Multimeter, check the Data Bus On Board Diagnostic Interface J533 electrical harness connector to the Engine Control Module
(ECM) J623 electrical harness connector T94 for resistance.
Data Bus On Board Diagnostic Engine Control Module
Interface J533 electrical harness (ECM) J623 Electrical
connector terminals harness connector T94 terminals or test box sockets
6 (Can_Bus Low) 67
19 (Can_Bus High) 68
2007 Audi Q7 Quattro V6-3.6L (BHK) Copyright © 2009, ALLDATA 9.90 Page 2
Specified value: 1.5 ohms Max.
If the specified value was not obtained:
- Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).
- Check the wiring connection for damage, corrosion, lose or broken terminals.
- If necessary, repair the faulty wiring connection.
If no malfunction is found in the wiring:
- Replace the Data Bus On Board Diagnostic Interface J533.
Final procedures
After repair work, the following work steps must be performed in the following sequence:
1. Check the DTC memory. See: Powertrain Management/Computers and Control Systems/Testing and Inspection/Scan Tool Testing and
Procedures/Mode 03: Interrogating Fault Memory
2. If necessary, erase the DTC memory. See: Powertrain Management/Computers and Control Systems/Testing and Inspection/Scan Tool
Testing and Procedures/Diagnostic Mode 04: Reset/Delete Diagnostic Data
3. If the DTC memory was erased, generate readiness code.
- End diagnosis.