BODY A-PISTON 9S4091 - Caterpillar

The following background information is related to this procedure:The CAN data links are also known as J1939 data links. A data link is an industry standard for sending data between different devices in the same application.High-speed data is transferred via the data links. The data links cannot be accurately tested without complicated equipment. The data links require a resistance of 60 Ohms between the two wires to transmit the data correctly. This resistance is made up of two 120 Ohm resistors. The two resistors are known as "Terminating Resistors". The terminating resistors should be at opposite ends of a data link circuit. If this resistance is not present, then the data will be intermittent or unreadable.Note: The wiring for a J1939 data link is a shielded twisted-pair cable. If the wiring is damaged, the replacement type must be shielded twisted-pair cable.-9 Detected Problems:ECM 1 is unable to communicate on the data link.
ECM 1 cannot communicate with other ECM's on the data link, but can communicate with the service tool. This situation indicates a problem with the data link wiring.ECM 1 is unable to communicate with ECM 2 on the data link.
ECM 1 cannot communicate with ECM 2, indicating a problem with the data link wiring, power or ground circuit, or ECM 2.
Illustration 1 g06151330
Typical example of the schematic for the CAN A data link
Illustration 2 g06151360
Typical example of the schematic for the CAN B data link
Illustration 3 g06151382
Typical example of the schematic for the CAN C data link
Illustration 4 g02453576
Typical view of the pin locations on the P1 connector
(34) CAN A-
(37) CAN C+
(38) CAN C-
(50) CAN A+
Illustration 5 g01980934
Typical view of the pin locations on the P2 connector
(21) CAN B-
(29) CAN B+
(30) CAN A+
(31) CAN A-Complete the procedure in the order in which the steps are listed.
Table 2
Troubleshooting Test Steps Values Results
1. Check for Associated Diagnostic Trouble Codes
A. Establish communication between the electronic service tool and the ECM. Refer to Troubleshooting, "Electronic Service Tools", if necessary.
B. Download the "Warranty Report" from the engine ECM before performing any troubleshooting or clearing diagnostic trouble codes.
Troubleshoot any associated diagnostic codes that are present before continuing with this procedure.
Associated Codes
Result: Another diagnostic trouble code is not active or logged.
Proceed to Test Step 2.
Result: Another code is active or logged.
Repair: Troubleshoot the other codes before continuing with this procedure.
Refer to Troubleshooting, "Diagnostic Trouble Codes" to troubleshoot the other diagnostic code.
2. Use the "System Communication Status" to Determine the Communication Issue
A. In the electronic service tool, click the "Diagnostics" tab on the tool bar.
B. Select the "System Communication Status" option from the drop-down list.
Component Identified
Result: A -9 or -2 code is active.
Repair: Refer to the above -9 detected problems for more information.
Proceed to Test Step 3.
3. Check the Power and Ground to the ECM
A. Turn the keyswitch to the ON position.
B. Measure the voltage between the battery (+) and battery (-) terminals on the wiring harness connector of the ECM. Refer to the appropriate wiring diagram.
Battery Voltage Result: The voltage is not equal to battery voltage.
There is an open