Can-Bus To Engine Control Module Checking

Special tools and workshop equipment required 

• Multimeter.
• Test lamp
• 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 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 ECM or other control modules connected to the CAN Bus.

Test procedure 

-- Perform a preliminary check to verify the customers complaint. Refer to PRELIMINARY CHECK 

Start diagnosis 

-- Disconnect the Engine Control Module (ECM) -J623- electrical harness connector. Refer to the Repair Information.

Turn the ignition switch ON.

-- Using a multimeter, check the Engine Control Module (ECM) -J623- electrical harness T94 connector terminal 68 (CAN Hi) to terminal 67 (CAN Lo) wires for voltage.

Specified value: 0.41 to 0.45 V (at approx. 20° C)

Turn the ignition switch OFF.

If the specified value was Not obtained:

-- Disconnect the Instrument Cluster Module - J285- electrical harness connector. Refer to the Repair Information.

-- Using a multimeter, check the Instrument Cluster Module - J285- electrical harness T32 connector terminals to the Engine Control Module (ECM) -J623- electrical harness T94 connector terminals for open circuit or short to ground.

Instrument Cluster Module - J285- electrical connector T32 terminals	Engine Control Module (ECM) -J623- electrical connector T94 terminals
20 (Can Bus Low)	67
19 (Can Bus High)	68

Specified value: Circuit resistance less than 1.5 Ω (at approx. 20° C) and no continuity to ground.

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 the specified value was obtained:

-- Using a multimeter or test lamp, check the power and ground inputs to the Engine Control Module (ECM) -J623-. Refer to the Wiring Diagram for pin locations of power and grounds.

If any of the power or grounds were Not present:

-- Repair the faulty power or ground circuit.

If the power or grounds were OK:

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

Final procedures 

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

1. Check the DTC memory. Refer to DIAGNOSTIC MODE 03 - READ DTC MEMORY .
2. If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
3. If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .