CAP 4T8058 - Caterpillar

If the 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 verifies 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 g02112358
Schematic for the Cat Data Link and the CAN data link
Illustration 2 g01672679
Terminal locations at the service tool connector
(A) +Battery
(B) −Battery
(C) CAN shield
(D) Cat Data Link +
(E) Cat Data Link −
(F) CAN data link −
(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 (if applicable)
(P1-50) CAN data link +
(P1-52) +Battery (if applicable)
(P1-53) +Battery (if applicable)
(P1-61) −Battery (if applicable)
(P1-63) −Battery (if applicable)
(P1-65) −Battery (if applicable)
(P1-70) Keyswitch
Illustration 4 g02078636
P2 ECM connector
(P2-11) CAN data link −
(P2-12) CAN data link + Test Step 1. Check for a Short Circuit
Turn the keyswitch to the OFF position.
Thoroughly inspect the connectors that are associated with the data link circuits. Refer to Troubleshooting, "Electrical Connectors - Inspect".
Disconnect the P1 and the P2 ECM connector.
Disconnect Cat ET from the service tool connector.
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.
Table 2
Resistance Measurements for the 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
P2-12 (CAN data link +) All of the other terminals on the P2 connector
Negative ground
P2-11 (CAN data link -) All of the other terminals on the P2 connector
Negative ground Results:
Each check of the resistance indicates an open circuit. - Proceed to Test Step 2.
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. -