Can-Bus Terminal Resistance, Checking
Special tools and workshop equipment required
- Multimeter.
- Wiring diagram.
Test requirement
- A CAN-Bus malfunction was recognized.
- The Motronic Engine Control Module (ECM) - J220- 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 (GND) connections between engine/transmission/chassis OK.
- Ignition switched off.
Function
The Motronic Engine Control Module (ECM) -J220- 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 Motronic Engine Control Module (ECM) -J220- 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) -J220-.
Procedure
-- Disconnect the Data Bus On Board Diagnostic Interface -J533- electrical harness connector.
The Motronic Engine Control Module (ECM) -J220- must remain connected for the following step.
-- Using a Multimeter, check the Data Bus On Board Diagnostic Interface -J533- electrical harness connector terminals 6 to 16 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 (GND).
-- Check the wiring connection for damage, corrosion, lose 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) -J220-. Refer to MOTRONIC ENGINE CONTROL MODULE, REPLACING .
If the specified value was obtained:
Checking wiring
If the manufacturers test box is being used. Perform the following step.
-- Install the test box. Refer to Repair information.
If the manufacturers test box is not being used. Perform the following step.
-- Remove the Motronic Engine Control Module (ECM) -J220-. Refer to MOTRONIC ENGINE CONTROL MODULE, REPLACING .
-- Using a Multimeter, check the Data Bus On Board Diagnostic Interface -J533- electrical harness connector to the Motronic Engine Control Module (ECM) -J220- electrical harness connector T94 for resistance.
| Data Bus On Board Diagnostic Interface -J533- electrical harness connector terminals | Motronic Engine Control Module (ECM) -J220- electrical connector T94 terminals or test box sockets |
|---|---|
| 6 (Can_Bus Low) | 67 |
| 16 (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 (GND).
-- Check the wiring connection for damage, corrosion, lose or broken terminals.
-- If necessary, repair the faulty wiring connection.
If no malfunction is found in the wiring:
-- Replace the Data Bus On Board Diagnostic Interface -J533-.
Final procedures
After repair work, the following work steps must be performed in the following sequence:
- Check the DTC memory. Refer to DIAGNOSTIC MODE 03 - READ DTC MEMORY .
- If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
- If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .
-- End of diagnosis.