System Operation Description:
Use this procedure to troubleshoot the electrical system if a problem is suspected with the following data links:
- Cat Data Link
- CAN data link (J1939)
- ATA data link
If the Caterpillar Electronic Technician (ET) will not communicate with the Electronic Control Module (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.
Background Information
Cat ET – Cat ET is the standard data link that communicates with the ECM and other modules.
CAN Data Link (J1939) – The CAN data link communicates engine information to other modules.
ATA Data Link – The ATA data link communicates ECM information to the electronic service tools.
Test Step 1. Inspect Electrical Connectors And Wiring
- Remove electrical power from the ECM.
Illustration 2 g01139425
ECM
(1) J1/P1 connectors
(2) J2/P2 connectors
- Thoroughly inspect connectors (1) and (2). Inspect the harness and all of the other connectors. Refer to Troubleshooting, “Electrical Connectors – Inspect” for details.
Illustration 3 g01432162
P1 ECM connector
(P1-1) ATA data link (-)
(P1-7) ATA data link (+)
(P1-3) Cat Data Link (-)
(P1-9) Cat Data Link (+)
(P1-39) CAN data link (-)
(P1-33) CAN data link (+)
- Perform a 45 N (10 lb) pull test on each of the wires that are associated with the ATA data link.
- Check the allen head screw on the ECM connectors and the customer connector. Refer to Troubleshooting, “Electrical Connectors – Inspect” for the correct torque value.
- Check the wiring harnesses for abrasion, for corrosion, and for pinch points.
Expected Result:
All connectors, pins, and sockets are completely inserted, and coupled. The harness and wiring are free of corrosion, of abrasion, and of pinch points.
Results:
- OK – The harness and the wiring appear to be OK. Proceed to Test Step 2.
- Not OK – There is a problem in the wiring harness.Repair: Complete the necessary repairs and/or replace parts, if necessary. Refer to Troubleshooting, “Electrical Connectors – Inspect”.
STOP
Test Step 2. Check the Wiring for the Data Links for a Short Circuit
- Remove electrical power from the ECM.
- Disconnect the ECM connector J1/P1 and J2/P2 at the ECM.
- Disconnect any control modules from the data links.
- Disconnect Cat ET from the service tool connector.
- Measure the resistance between the following terminals:
- P1-7 (ATA data link +) and every terminal on ECM connectors P1 and P2
- P1-7 (ATA data link +) and chassis ground
- P1-1 (ATA data link -) and every terminal on ECM connectors P1 and P2
- P1-1 (ATA data link -) and chassis ground
- P1-33 (CAN data link +) and every terminal on ECM connectors P1 and P2
- P1-33 (CAN data link +) and chassis ground
- P1-39 (CAN data link -) and every terminal on ECM connectors P1 and P2
- P1-39 (CAN data link -) and chassis ground
- P1-9 (Cat Data Link +) and every terminal on ECM connectors P1 and P2
- P1-9 (Cat Data Link +) and chassis ground
- P1-3 (Cat Data Link -) and every terminal on ECM connectors P1 and P2
- P1-3 (Cat Data Link -) and chassis ground
Expected Result:
Each measurement indicates an open circuit.
Results:
- OK – Each measurement indicates an open circuit. The wiring for the data links does not have a short circuit. Proceed to Test Step 3.
- Not OK – At least one measurement indicates a short circuit. The wiring for a data link has a short circuit.Repair: Determine the cause of the short circuit. Repair the problem, when possible. Replace parts, if necessary. Verify that the problem is resolved.
STOP
Test Step 3. Check the Wiring for the Data Links for an Open Circuit
- Connect a jumper wire between terminals P1-1 and P1-7.
- At the service tool connectors, measure the resistance between the terminals for the ATA data link.
- Connect a jumper wire between terminals P1-3 and P1-9.
- At the service tool connectors, measure the resistance between the terminals for the Cat Data Link.
- Connect a jumper wire between terminals P1-39 and P1-33.
- Measure the resistance at the connectors of every control module on the CAN data link.
Expected Result:
All of the resistance measurements indicate a short circuit.
Results:
- OK – All of the resistance measurements indicate a short circuit. The wiring for the data links does not have an open circuit. Proceed to Test Step 4.
- Not OK – One of the resistance measurements indicate a open circuit.Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
STOP
Test Step 4. Check the Termination Resistors for the Can Data Link
Note: Perform this test step only if you are troubleshooting a problem with the CAN data link. Otherwise, proceed to the next test step.
- Verify that the terminating resistors are installed on the ends of the data link.
- Disconnect the J1/P1 ECM connector and measure the resistance between P1-33 (CAN data link +) and P1-39 (CAN data link -).
Expected Result:
The resistance is between 57 and 63 Ohms.
Results:
- OK – The resistance is within the range. Proceed to Test Step 5.
- Not OK – The range of the resistance is 114 Ohms to 126 Ohms.Repair: If a termination resistor is missing, install the missing resistor. If both resistors are present, measure the resistance between pin A and pin B of the termination resistor. Replace the termination resistor if the range of resistance is not 114 Ohms to 126 Ohms.
STOP
Test Step 5. Disconnect the Modules and Check for Communication
- Disconnect all of the modules from the data links.
- Connect a module. Attempt to establish communication with the module. Perform this procedure for every module.
Expected Result:
Communication could be established with every module.
Results:
- OK – Communication could be established with every module.Repair: The problem may be intermittent. If the problem is intermittent, refer to Troubleshooting, “Electrical Connectors – Inspect”.
STOP
- Not OK – Communication could not be established with every module.Repair: Replace the module(s) or the device(s). Verify that the problem is resolved.
STOP