Can-Bus Terminal Resistance, Checking

WARNING: This page is about a different car, the 2015 Audi A4 Quattro, 2014 Audi A4 Quattro, and 2013 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.

General Description

The Engine Control Module -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 -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 -J623-.

Special tools and workshop equipment required

Multimeter
Wiring Diagram

Test requirements

Fuses OK.
Battery voltage OK.
Switch OFF all electrical and electronic accessories.
Vehicles with Auto. Transmission, ensure Selector Lever position is in "P".
Vehicles with Man. Transmission, ensure Shifter Lever position is in "N" with Parking Brake applied.
Coolant Temperature: ≥ 80° C.
Observe all safety precautions: SAFETY PRECAUTIONS .
View clean working conditions: CLEAN WORKING CONDITIONS .
For Hybrid vehicles refer to: HIGH VOLTAGE SYSTEM GENERAL WARNINGS .

Test Procedure

Step	Procedure	Result / Action to Take
1	PERFORM: Preliminary Check to verify the customers complaint. Refer to PRELIMINARY CHECK . -- Was Complaint verified?	-- YES: GO TO: Step 2 -- NO: GATHER more information from customer about the complaint.
2	IGNITION: OFF. DISCONNECT: Data Bus On Board Diagnostic Interface -J533- harness connector. The Engine Control Module -J623- must remain connected for the following step. CHECK: Data Bus On Board Diagnostic Interface -J533- harness connector terminals 6 to 16 for resistance. Specified value: 60 to 72 Ω (at approx. 20° C). -- Was Value obtained?	-- YES: CONDITION: May be intermittent. PERFORM: Visual Inspection of wiring and component. CHECK: Wiring for open, high resistance, short or harness connector for damage, corrosion, loose or broken terminals. REPAIR: Faulty wiring or connector. GO TO: Step 4 -- NO: GO TO: Step 3
3	REMOVE: Engine Control Module - J623-. Refer to appropriate repair information. CHECK: Data Bus On Board Diagnostic Interface -J533- harness connector terminal 6 to the Engine Control Module - J623- harness connector T94 / 67 for resistance. CHECK: Data Bus On Board Diagnostic Interface -J533- harness connector terminal 16 to the Engine Control Module - J623- harness connector T94 / 68 for resistance. SPECIFIED VALUE: 0.5 Ω (± 0.3 Ω). -- Were Values obtained?	-- YES: REPLACE: Engine Control Module -J623-. Refer to appropriate repair information. GO TO: Step 4 -- NO: PERFORM: Visual Inspection of wiring and component. CHECK: Wiring for open, high resistance, short or harness connector for damage, corrosion, loose or broken terminals. REPAIR: Faulty wiring or connector. GO TO: Step 4
4	Final Procedure Perform a road test to verify repair. -- Does the original DTC return?	-- YES: CHECK: Engine Control Module -J623- harness connector for any damaged, pushed-out pins. REPAIR: As necessary. If all electrical connections are OK: REPLACE: Engine Control Module -J623-. Refer to appropriate repair information. Clear the DTC's. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY . Repair is complete. Generate Readiness Code. Refer to READINESS CODE . Return vehicle to Customer. -- NO: Perform the diagnostic procedure for any DTC's. If no DTC's return the repair is complete. Return vehicle to customer.