Volvo XC60 Medium Speed CAN Bus Failure

This 2017 Volvo XC60 with a 2-litre engine (B4204T11) had multiple electrical failures reported by the owner. These were all relating to the Body electrical system. The faults were intermittent in nature. When the issue was present the following sub-systems failed to operate:

• Remote Keyless Entry.
• Instrument Panel.
• Electronic Climate Control.
• Infotainment system.
• Central Locking.
• Electric Windows.
• Power Mirrors.
• Directional Indicators.
• Power Tailgate.

The vehicle would start and operate as expected even with the issue present. A Scan Tool was connected to the vehicle’s Data Link Connector (DLC) and numerous fault codes were stored. The following codes were found with a full system Code Scan:

Module	Fault Code ID	Fault Code Title
Central Electronic Module	U015500	Lost Communication with Driver Information Module
Central Electronic Module	U016400	Lost Communication with Climate Control Module
Central Electronic Module	U019900	Lost Communication with Driver Door Module
Central Electronic Module	U020000	Lost Communication with Passenger Door Module
Central Electronic Module	U001011	Medium Speed CAN Bus - Short to Ground
Central Electronic Module	U001088	Medium Speed CAN Bus – Bus Off
Central Electronic Module	U021400	Lost Communication with Keyless Vehicle Module
Central Electronic Module	U023000	Lost Communication with Power Tailgate Module
Supplementary Restraint Module	U015500	Lost Communication with Driver Information Module
Driver Information Module	U001088	Medium Speed CAN Bus – Bus off
Driver Information Module	U210000	Control Module Unconfigured
Driver Door Module	U001000	Medium Speed CAN Bus – General Fault
Driver Door Module	U014000	Lost Communication with Central Electronic Module
Driver Door Module	U016487	Lost Communication with Climate Control module
Passenger Door Module	U001000	Medium Speed CAN Bus – General Fault
Passenger Door Module	U014000	Lost Communication with Central Electronic Module
Passenger Door Module	U016487	Lost Communication with Climate Control module
Climate Control Module	U001088	Medium Speed CAN Bus – Bus off
Climate Control Module	U014000	Lost Communication with Central Electronic Module
Infotainment Control Module	U001000	Medium Speed CAN Bus – General Fault
Keyless Vehicle Module	U001000	Medium Speed CAN Bus – General Fault
Power Operated Tailgate	U001000	Medium Speed CAN Bus – General Fault
Power Operated Tailgate	U210000	Control Module Unconfigured

 

A wiring diagram was consulted to investigate the modules which communicate on the Medium Speed data bus. The diagram below is a simplified diagram showing the modules on the Mid speed network.

CEM – Central Electronic Module.

CCM – Climate Control module.

ICM – Infotainment Control Module.

DIM – Driver Information module.

DDM – Driver Door Module.

PDM – Passenger Door Module.

KVM – Keyless Vehicle Module.

POT – Power Operated Tailgate.

 

It can also be seen from the diagram that pin 3 and 11 at the Data Link Connector (DLC) are connected to the Medium Speed CAN Bus. This is a very convenient point to test the network. A 16 pin break-out box can be used to allow easy access to the DLC pins.

An oscilloscope was connected to the breakout box and the following waveform was observed when the faults were present.

• Yellow Channel – Pin 3.
• Green Channel – Pin 11.

It can be seen from this waveform that there is no activity on the network and the voltage is close to ground potential.

This issue can occur due to a module internally shorting the network to ground or a wiring fault creating the short circuit. One of the more common areas on a vehicle for wiring problems is the wiring loom where it enters the doors. As faults were present in both the Driver and Passenger Door Modules this was the first area to be investigated. The wiring to both the driver and passenger door was undamaged and disconnecting one door at a time did not resolve the issue.

Another common failure on modern vehicles is the instrument cluster. On this particular vehicle the cluster is relatively easy to remove and disconnect the electrical connector. No issue was found here and with the module disconnected the network did not become active.

The next part of the network to be investigated was the Climate Control Module. It was noticed that the CAN signal was intermittently present while the CCM was being removed from the dash. Applying hand pressure to the dashboard resolved the issue, removing the hand from the dash resulted in the fault re-appearing. This is indicative of a wiring fault and in particular a wire(s) shorting against a vehicle ground. The CCM, glovebox, radio and various trim panels were removed to inspect the wiring.

  

One of the Mid Speed CAN Bus network wires was found to be touching a metal bracket behind the radio.

                   

 

The wiring was repaired and a foam pad attached to the metal bracket for additional protection against future issues.

The CAN network now preformed as expected.

Mid Speed CAN Bus data signal

Data Transfer Speed calculated from End of Frame Bit (EOF) – 125 Kbits per Second.

Differential Voltage between CAN High and Low – Mid Speed CAN Bus Network.

The fault codes were erased and the vehicle reassembled. A Road test was carried out and the vehicle preformed as expected. This repair would have been very difficult without the correct wiring diagram for the vehicle, a scan tool to access the fault codes in each system and an oscilloscope to monitor the CAN bus signal.