Can Bus Terminal Resistance, Checking

Observe all safety precautions: SAFETY PRECAUTIONS 

View clean working conditions: CLEAN WORKING CONDITIONS 

Prior to repair work, perform a preliminary check to verify the condition. Refer to PRELIMINARY CHECK .

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 and workshop equipment 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 

-- 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.

Data Bus On Board Diagnostic Interface -J533- electrical harness T20 D connector terminals	Direct Shift Gearbox (DSG) Mechatronic -J743- electrical harness connector T20 E terminals or test box sockets
6 Data -	15
16 Data +	10

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

If the specified value was not obtained:

Checking wiring 

-- Remove the Motronic Engine Control Module (ECM) -J623-. Refer to the service information for removal and installation procedures.

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

Data Bus On Board Diagnostic Interface -J533- electrical harness T20 D connector terminals	Motronic Engine Control Module (ECM) electrical harness connector T94 terminals or test box sockets
6	67
16	68

Specified value: 1.5 Ω 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-. Refer to the service information for removal and installation procedures.

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 .
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 .