Can Bus Terminal Resistance, Checking

Function

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. Refer to: SAFETY PRECAUTIONS .
View clean working conditions. Refer to: CLEAN WORKING CONDITIONS .

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 CAN-BUS TERMINAL RESISTANCE, CHECKING . -- NO: GATHER more information from customer about the complaint.
2	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 T20e / 6 to T20e / 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 CAN-BUS TERMINAL RESISTANCE, CHECKING . -- NO: GO TO Step 3 CAN-BUS TERMINAL RESISTANCE, CHECKING .
3	REMOVE: Engine Control Module - J623-. Refer to appropriate repair service information. CHECK: Faulty Data Bus On Board Diagnostic Interface -J533- harness connector terminal T20e / 6 to the Engine Control Module - J623- harness connector T94 / 67 for resistance. CHECK: Faulty Data Bus On Board Diagnostic Interface -J533- harness connector terminal T20e / 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 service information. GO TO Step 4 CAN-BUS TERMINAL RESISTANCE, CHECKING . -- NO: CHECK: Wiring for open, high resistance, short or harness connector for damage, corrosion, loose or broken terminals. If no malfunction is found in the wiring: REPLACE: Data Bus On Board Diagnostic Interface -J533-. Refer to appropriate repair service information. GO TO Step 4 CAN-BUS TERMINAL RESISTANCE, CHECKING .
4	Final Procedure Perform a road test to verify repair. Do any DTC's return:	-- YES: Check the DTC memory. Refer to: DIAGNOSTIC MODE 03 - READ DTC MEMORY . Perform the diagnostic procedure for that DTC. -- NO: Repair is complete. Generate readiness code. Refer to: READINESS CODE . Return vehicle to Customer.