Scan Tool Will Not Communicate With Can Bus

WARNING: This page is about a different car, the 2021 Jeep Grand Cherokee L. However, it is still accessible from the selected car via links, so may be relevant.

NOTE:

This procedure diagnoses CAN Bus circuits after the Security Gateway (SGW) Module.

NOTE:

If the vehicle operates, but the scan tool topology screen indicates all ECUs on a CAN Bus do not communicate, proceed to SCAN TOOL DOES NOT COMMUNICATE WITH VEHICLE. Refer to SCAN TOOL WILL NOT COMMUNICATE WITH VEHICLE .

NOTE:

Due to the loss of communication on the CAN Bus, multiple ECUs may not communicate on the network and certain U-code DTCs, such as CAN BUS OFF, CAN BUS MISSING MESSAGE or CAN BUS NO SIGNAL, may not be displayed as Active on the scan tool until the cause of the fault is repaired.

CAN BUS FAULTS

CAN BUS FAULT TYPES
LOSS OF COMMUNICATION	Set by an active receiving/reporting ECU that does not detect communication from another ECU that is connected to the same CAN Bus network. Insufficient power, ground, bus voltage, or inaccurate vehicle configuration will cause a loss of communication.
IMPLAUSIBLE MESSAGE	Set by an active receiving/reporting ECU that determines the CAN Bus network data from the transmitting/offending ECU is missing part of the message, or the message is an irrational value.
MISSING MESSAGE	Set by an active receiving/reporting ECU that determines the CAN Bus network data message is missing partial information when sent from the active transmitting/offending ECU.
BUS OFF	Set by an ECU that has experienced approximately 32 transmit errors. This may be due to ECU internal faults as well as external bus faults, such as a shorted circuit or when connecting and disconnecting testing tools to the diagnostic connector.
PHYSICAL	Only detected by ECUs equipped with a transceiver that is able to detect shorted bus circuits. ECUs not equipped with this detection may instead set bus off faults, due to shorted bus circuit(s).

If the vehicle does not operate properly and the scan tool topology screen indicates all ECUs on a CAN Bus do not communicate, perform the appropriate Body Control Module (BCM) CAN BUS OFF, CAN BUS MISSING MESSAGE or CAN BUS NO SIGNAL U-code diagnostic procedure for the CAN Bus being diagnosed. Refer to DIAGNOSTIC CODE INDEX .