Can-Bus Terminal Resistance, Checking Audi TT 8N

Special tools, testers and auxiliary items required

1. Multimeter.
2. Wiring diagram.

Test requirement

1. A CAN-Bus malfunction was recognized.
2. The Motronic Engine Control Module (ECM) J220 fuses OK.
3. Battery voltage at least 12.5 volts.
4. All electrical consumers such as, lights and rear window defroster, switched off.

1. Vehicles with automatic transmission, shift selector lever into position "P" or "N".
2. A/C switched off.
3. Ground (GND) connections between engine/transmission/chassis OK.
4. 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

1. Disconnect the Data Bus On Board Diagnostic Interface J533 electrical harness connector.

Note. The Motronic Engine Control Module (ECM) J220 must remain connected for the following step.

1. Using a Multimeter , check the Data Bus On Board Diagnostic Interface J533 electrical harness connector terminals 18 to 19 for resistance.

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

If the specified value was not obtained

1. Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).
2. Check the wiring connection for damage, corrosion, loose or broken terminals.
3. If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring

1. Replace the Motronic Engine Control Module (ECM) J220. Refer to --> «Motronic Engine Control Module (ECM) J220, Replacing»(ref-276276-S39982482672008010300000) .

If the specified value was obtained

Checking wiring

If the manufacturers test box is being used. Perform the following step.

1. Install the Test Box 105 Pin VAG1598/31. Refer to --> «24 MULTIPORT FUEL INJECTION (MFI)»(ref-276275-S13244009452008010300000)

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

1. Remove the Motronic Engine Control Module (ECM) J220. Refer to --> «Motronic Engine Control Module (ECM) J220, Replacing»(ref-276276-S39982482672008010300000) .
2. 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 for resistance.

Specified value: 1.5 ohms Max.

If the specified value was not obtained

1. Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).
2. Check the wiring connection for damage, corrosion, loose or broken terminals.
3. If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring

1. 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

1. Check the DTC memory.
2. If necessary, erase the DTC memory. Refer to «Diagnostic Mode 04: Reset/Delete Diagnostic Data»(ref-276276-S31279847122008010300000) .
3. If the DTC memory was erased, generate readiness code. Refer to «Readiness Code»(ref-276276-S05799074302008010300000) .

End of diagnosis.