CAN-Bus System, Checking
CAN-bus System, Checking
NOTE:
- If the connector is removed from one control module connected to the CAN-bus-Comfort and the ignition is switched on, a malfunction entry can occur in another control module connected to the CAN-Bus. The same applies, if e.g. by pulling a fuse the voltage supply is interrupted.
- The Control module with indicator unit in instrument cluster -J285- is the decisive control module in the CAN-bus system, via the adaptation control modules connected to the CAN-bus system are entered into this control module (-J285-) (depending on equipment level).
- Based on the wiring diagram on can determine how many control modules are connected to the CAN-bus system.
Isolating possible malfunction causes
NOTE:
The following malfunction locations and malfunction types apply for the CAN-bus system:
- Powertrain CAN-bus
- Faulty: No data can be transferred via the Bus- system. No data can be transferred on either one or both lines (CAN-Hi or CAN-Lo).
- Check DTC memory: Control module with indicator unit in instrument cluster -J285- cannot send information, due to a malfunction on a control module connected to the CAN-bus system (Check DTC memory of instrument cluster control module).
- Missing messages (time out for various control modules): No data was received by one or more control modules within a specified time period.
- Control module with indicator unit in instrument cluster -J285-
- No communication. No data received from Control module with indicator unit in instrument cluster -J285-.
- Check DTC memory: Control module with indicator unit in instrument cluster -J285- cannot send information due to malfunction on an component connected in series.
Determine malfunction in CAN-bus system
- With ignition switched off, connect VAS 5051 Vehicle Diagnostic, Testing and Information System with diagnostic cable VAS 5051/1 to 16-pin diagnostic connector on vehicle. Refer to "Scan Tool Testing/Scan Tool Connecting and Initial Checks" under "Heating and Air Conditioning", Testing and Inspection
- Switch ignition on.
- Press button -0- twice for function "Automatic test procedure".
Indicated on display of VAS 5051:
All address words stored in VAS 5051 are sent to the vehicle one after another via the diagnostic cable.
Indicated on display of VAS 5051:
- Display field 1 shows which address word is currently transferred to VAS 5051.
- Display field -2- shows which control modules answered. In addition the amount and type of malfunction stored in that control module is displayed.
- Wait until "Function ended" is shown in display field -1-.
NOTE:
- Before checking the CAN-bus wiring system, check whether a malfunction is stored in a control module which cannot exchange data with other control modules and eliminate malfunction as necessary.
- The data exchange with other control modules can be interrupted, if a control module stores a malfunction, although this malfunction may not apply to the CAN-bus-system.
- Check part number with index of control module that does not communicate.
Malfunction is indicated only by A/C Control Head -E87-
- Check coding of A/C Control Head -E87-. Refer to "A/C Control Head -E87-, Coding - I" under "Heating and Air Conditioning", Testing and Inspection
- Check data lines (wires) to A/C Control Head - E87- for open circuit or wiring resistance.
Wire resistance: max: 1.5 Ohm
NOTE: Watch for possible loose contact in the wiring and connectors.
If no coding or wiring problem can be determined, malfunction is in A/C Control Head -E87-.
Malfunction indicated in another control module:
- Check data wires and respective shield between the different control modules connected to the CAN-bus system for open circuit and wiring resistance.
Wire resistance: max: 1.5 Ohm
- Check data wires and respective shield between the different control modules connected to the CAN-bus system for short circuit against each other, short to B+ and Ground (GND).
NOTE:
- Watch for possible loose contact in the wiring and connectors.
- If this malfunction is not displayed on all connected control modules, it is possible that there is an open circuit at one connecting point in wiring.
If no malfunction is determined and all control modules connected to the CAN-bus system show malfunction, there is a malfunction in one of the other connected control modules.
- Check version, coding and the entered adaptation of Control module with indicator unit in instrument cluster -J285-.
- Check version and coding of other control modules connected to the CAN-bus system.
- Disconnect all control modules from CAN-bus system except the instrument cluster and/or A/C Control Head -E87-.
- Erase DTC memory of instrument cluster and A/C Control Head -E87-.
- Check DTC memory of instrument cluster and A/C Control Head -E87-.
If this malfunction no longer appears, malfunction lies in one of the connected control modules.
- Connect in sequence the different control modules again.
- Check DTC memory after connecting each control module.
- Replace control module if malfunction appears again after it has been connected again.
If this malfunction appears again, there is a malfunction in the instrument cluster or A/C Control Head -E87-.
- Disconnect A/C Control Head -E87- and connect another (e.g. engine control module).
- Erase DTC memory of Instrument Cluster and Engine Control Module (ECM).
- Check DTC memory of Instrument Cluster again.
NOTE: By disconnecting the A/C Control Heed -E87- and connecting another control module, a faulty module can be detected.
- Replace faulty control module