CAN Bus Terminal Resistance, Checking

CAN Bus Terminal Resistance, Checking

Special tools, testers and auxiliary items required

• Multimeter

• Wiring diagram.

Test requirements

• 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 connections between engine/transmission/chassis OK.

• Ignition switched Off.

Test procedure

- Observe safety precautions. Refer to => [ Safety Precautions ] Safety Precautions

- Observe Clean Working Conditions. Refer to => [ Clean Working Conditions ] Clean Working Conditions

- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check.

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).

Procedure

- Disconnect the Data Bus On Board Diagnostic Interface (T32b) electrical harness connector.

• 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 T20 connector, terminals 6 to 16 for resistance.

Specified value: 58 to 70 ohms (at approx. 20° C)

If the specified value was Not obtained:

- Remove the Engine Control Module (ECM) (J623). Refer to the Repair Information.

- Using a multimeter, check the Data Bus On Board Diagnostic Interface (J533) electrical harness connector T20 to the Engine Control Module (ECM) (J623) electrical harness connector T94 for resistance.






Specified value: 1.5 ohms Max.

If the specified value was not obtained:

- Check the wiring connection for an open circuit, high resistance or short circuit to voltage or ground.

- Check the wiring connection for damage, corrosion, loose 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 no malfunction is detected in the wiring and the resistance check was OK:

- Replace the Data Bus On Board Diagnostic Interface (J533). Refer to the Repair Information.

- Assembly is performed in the reverse of the removal.

Final procedures

After repair work, the following work steps must be performed in the mentioned sequence:

1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Modes 01 - 09.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Monitors, Trips, Drive Cycles and Readiness Codes.