ARM AS 2G8813 - Caterpillar

Note: This procedure checks for an open or for a short in the data link circuits.If Caterpillar Electronic Technician (ET) will not communicate with the ECM, refer to Troubleshooting, "Electronic Service Tool Does Not Communicate" before you begin this procedure. The procedure will verify that electrical power is being supplied to the ECM and to the service tool connector.The data links are used to communicate information between the engine ECM and other control modules that are a part of the application. Cat ET also communicates with the ECM via the data links.The service tool connector contains connections for electrical power and for the data links.When the keyswitch is in the OFF position, Cat ET may communicate with the ECM. However, the communications may be disrupted and the communications may require frequent reconnection. In order to avoid this problem, place the keyswitch in the ON position when Cat ET is being used.Cat ET may display the following error message:"The version of the ECM is not recognized and the integrity of the changed parameters and displayed data is not guaranteed."This message indicates that one of the following conditions exist:
The flash file in the ECM is newer than the version of Cat ET.
The latest version of Cat ET has not been installed.
Illustration 1 g02138795
Schematic for the Cat Data Link
Illustration 2 g01672679
Terminal locations at the service tool connector
(Terminal A) +Battery
(Terminal B) −Battery
(Terminal C) CAN shield
(Terminal D) Cat Data Link +
(Terminal E) Cat Data Link −
(Terminal F) CAN data link −
(Terminal G) CAN data link +
Illustration 3 g01672676
Terminal locations at the P1 ECM connector that are for the data link
(P1-8) Cat Data Link +
(P1-9) Cat Data Link −
(P1-34) CAN data link −
(P1-42) CAN shield
(P1-48) +Battery
(P1-50) CAN data link +
(P1-52) +Battery
(P1-53) +Battery
(P1-61) −Battery
(P1-63) −Battery
(P1-65) −Battery
(P1-70) Keyswitch
Table 2
Resistance Measurements for the Cat Data Link
Connector and Terminal Terminal
P1-8 (Cat Data Link +) All of the other terminals on the P1 connector
Negative ground
P1-9 (Cat Data Link -) All of the other terminals on the P1 connector
Negative ground
P1-50 (CAN data link +) All of the other terminals on the P1 connector
Negative ground
P1-34 (CAN data link -) All of the other terminals on the P1 connector
Negative ground
Table 3
Troubleshooting Test Steps Values Results
1. Check for a Short Circuit
A. Turn the keyswitch to the OFF position.
B. Thoroughly inspect the connectors that are associated with the data link circuits. Refer to Troubleshooting, "Electrical Connectors - Inspect".
C. Disconnect the J1/P1 ECM connectors.
D. Disconnect Cat ET from the service tool connector.
E. Measure the resistance between the points that are listed in Table 2. Be sure to wiggle the wires in the harnesses as you make each resistance measurement.
Open Circuit
Result: Each check of the resistance indicates an open circuit.
Proceed to Test Step 2.
Result: At least one check of the resistance does not indicate an open circuit. There is a short circuit in the harness or in a connector.
Repair: Repair the connectors and/or the wiring. Replace parts, if necessary.
If the problem is not resolved, proceed to Test Step 2.
2. Check for an Open Circuit
A. Fabricate a jumper wire that