Section 19 (Electronic Control Modules (Service Information)): Communication: Operation: Operation
The primary communication network between electronic control modules on this vehicle is the Controller Area Network (CAN) data bus system. The Controller Area Network (CAN) data bus allows all electronic modules connected to the bus to share information with each other. Regardless of whether a message originates from a module on the higher speed CAN C (500K) Bus or on the lower speed CAN Interior High Speed (IHS) (125K) Bus the message structure and layout is similar, which allows the Body Control Module (BCM) to be a Central Gateway to process and transfer messages between the CAN C and CAN IHS buses. The BCM also stores Diagnostic Trouble Codes (DTCs) for certain bus network faults.
The CAN bus nodes are connected in parallel to the two-wire bus using a twisted pair, where the wires are wrapped around each other to provide shielding from unwanted electromagnetic induction, thus preventing interference with the relatively low voltage signals being carried through them. The twisted pairs have between 33 and 50 twists per meter (yard). While the CAN bus is operating (active), one of the bus wires will carry a higher voltage and is referred to as the CAN High or CAN bus (+) wire, while the other bus wire will carry a lower voltage and is referred to as the CAN Low or CAN bus (-) wire. Refer to the CAN Bus Voltages table.
| CAN Bus Voltages (Normal Operation) | ||||||||
|---|---|---|---|---|---|---|---|---|
| CAN-C Bus Circuits | Sleep | Recessive (Bus Idle) | Dominant (Bus Active) | CAN-L Short to Ground | CAN-H Short to Ground | CAN-L Short to Battery | CAN-H Short to Battery | CAN-H Short to CAN-L |
| CAN-L (-) | 0 V | 2.4 - 2.5 V | 1.3 - 2.3 V | 0 V | 0.3 - 0.5V | Battery Voltage | Battery Voltage Less 0.75 V | 2.45 V |
| CAN-H (+) | 0 V | 2.4 - 2.5 V | 2.6 - 3.5 V | 0.02 V | 0 V | Battery Voltage Less 0.75 V | Battery Voltage | 2.45 V |
| CAN-IHS Bus Circuits | Key-Off (Bus Asleep) | Key-On (Bus Active) | CAN-L Short to Ground | CAN-H Short to Ground | CAN-L Short to Battery | CAN-H Short to Battery | CAN-H Short to CAN-L | |
| CAN-L (-) | 0.0V | 1.3 - 2.3 V | 0 V | 0.3 - 0.5 V | Battery Voltage | Battery Voltage Less 0.75 V | 2.45 V | |
| CAN-H (+) | 0.0 V | 2.6 - 3.5 V | 0.02 V | 0 V | Battery Voltage Less 0.75 V | Battery Voltage | 2.45 V | |
| Notes | ||||||||
| All measurements taken between node ground and CAN terminal with a standard DVOM. | ||||||||
| DVOM will display average network voltage. | ||||||||
| Total resistance of CAN networks can be measured with the battery disconnected. The average resistance is approximately 60 Ohms. The termination resistors are integral to the Star Connectors. | ||||||||
The CAN-IHS bus network remains active until all nodes on that network are ready for sleep. This is determined by the network using tokens in a manner similar to polling. When the last node that is active on the network is ready for sleep, and it has already received a token indicating that all other nodes on the bus are ready for sleep, it broadcasts a bus sleep acknowledgment message that causes the network to sleep. Once the CAN-IHS bus network is asleep, any node on the bus can awaken it by transmitting a message on the network.
In the CAN system, available options are configured into the BCM at the assembly plant, but additional options can be added in the field using the diagnostic scan tool. The configuration settings are stored in non-volatile memory. The BCM also has two 64-bit registers, which track each of the as-built and currently responding nodes on the CAN-B and CAN-C buses. The BCM stores a Diagnostic Trouble Code (DTC) in one of two caches for any detected active or stored faults in the order in which they occur. One cache stores powertrain (P-Code), chassis (C-Code) and body (B-Code) DTCs, while the second cache is dedicated to storing network (U-Code) DTCs.