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.

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

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

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-.

-- 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, 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 Selector Lever -E313-.

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 .