CAN Bus Terminal Resistance, Checking

CAN Bus Terminal Resistance, Checking

Observe all safety precautions: => [ Safety Precautions ] Generic Scan Tool

View clean working conditions: => [ Clean Working Conditions ] Clean Working Conditions

Use only gold-plated terminals when servicing any component with gold-plated electrical harness connector terminals.

For wiring diagrams, component locations, and connector views, Refer to the applicable wiring diagram.

Special tools, testers and auxiliary items required

• Multimeter

• Wiring diagram

Test requirement

• A CAN bus malfunction was recognized

• The module that does not communicate has all power and grounds present.

• Battery voltage at least 12.5 volts

• All electrical consumers switched off

• Vehicles with automatic transmission, shift selector lever in park or neutral

• A/C switched off

• Ground connections between engine/transmission/chassis OK

• Ignition switched off

Test procedure

• The engine control module must remain connected for the following step.

- Using a multimeter, measure the resistance between the CAN bus low and CAN bus high in the CAN bus disconnection plug electrical connector. Refer to Wiring Diagrams for location.

- Disconnect the transmission control module electrical connector.

- Using a multimeter, measure the resistance between the CAN bus low and CAN bus high from the transmission control module.

Specified value: 60 to 72 ohms (at approx. 20° C)

If the specified value was not obtained:

Checking wiring

- Remove the Motronic Engine Control Module (ECM) (J623).

- Using a multimeter, measure the resistance of the CAN bus low and CAN bus high circuits. Refer to Wiring Diagrams for location.

Specified value: 1.5 ohms Max.

If the specification was not obtained:

- Check the wires for a short circuit to each other, a short to battery voltage, and a short to ground.

- Check the electrical harness connector for damage, corrosion, loose or broken terminals.

- Repair as necessary.

If no malfunction is found in the wiring:

- Replace the Motronic Engine Control Module (ECM) (J623).

Final procedures

After 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 ] 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 ] Programming and Relearning.