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Total OBD & ECU Auto Diagnostics

Total OBD & ECU Auto Diagnostics

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(a) Two different CAN busses are used. The CAN busses are classified into two types based on typical communication speed.

The HS-CAN bus is a high-speed communication bus that is used for powertrain, chassis, and some body electrical communication. The HS-CAN bus is referred to as the "CAN bus" and it operates at speeds of approximately 500 kbps. Terminating resistors for the HS-CAN bus are located in the ECM and combination meter. The MS-CAN bus is a medium-speed communication bus that is used for body electrical communication. The MS-CAN bus is referred to as the "MS bus" and it operates at speeds of approximately 250 kbps. Terminating resistors for the MS-CAN bus are located in the main body ECU and the certification ECU. The resistance of the MS-CAN bus cannot be measured from the DLC3 connector.

Communication between these two networks is handled via the main body ECU, which acts as a gateway ECU.

(b) By pairing the CANH and CANL bus wires, the CAN performs communication based on differential voltage.

(c) Many ECUs (sensors) installed on the vehicle operate by sharing information and communicating with each other.

(d) The CAN has two resistors of 120 Q which are necessary to enable communication on the main bus wire.

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