Can-Bus Terminal Resistance, Selector Lever To MOTRONIC Engine Control Module, Checking

Special Tools And Workshop Equipment Required 

• Multimeter.
• Wiring diagram.

Test requirement 

• A CAN-Bus malfunction was recognized.
• The Motronic Engine Control Module (ECM) - J623- fuses OK.
• The Selector Lever -E313- 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 Motronic Engine Control Module (ECM) -J623- communicates with the Selector Lever -E313-.

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

Test Procedure 

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

Start diagnosis 

-- Remove the selector mechanism, far enough to gain access to the Selector Lever -E313- electrical harness connector -A-. Refer to the appropriate Service Information.

-- Disconnect the Selector Lever -E313- electrical harness connector -A-.

-- Using a multimeter, check the Selector Lever -E313- electrical harness connector terminals 7 to 8 for resistance.

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

If the specified value was not obtained: 

-- Check the wiring connection for an open circuit, short circuit to Battery (+) 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 Motronic Engine Control Module (ECM) -J623-. Refer to the appropriate Service Information.

If the specified value was obtained: 

Checking wiring

If the manufacturers test box is being used, perform the following step.

-- Install the test box.

If the manufacturers test box is not being used, perform the following step.

-- Remove the Motronic Engine Control Module (ECM) -J623-. Refer to the appropriate Service Information.

-- Using a multimeter, check the Selector Lever -E313- electrical harness connector to the Motronic Engine Control Module (ECM) -J623- electrical harness connector T94 for resistance.

Selector Lever -E313- electrical harness connector terminals	Motronic Engine Control Module (ECM) -J623- electrical connector T94 terminals or test box sockets
8 (Can-Bus Low)	67
7 (Can-Bus High)	68

Specified value: 1.5 Ω Max. 

If the specified value was not obtained: 

-- Check the wiring connection for an open circuit, short circuit to Battery (+) 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 Selector Lever -E313-. Refer to the appropriate Service 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 .