Use this procedure to troubleshoot the CAN data link if a problem with the wiring is suspected.
The CAN data link is used to communicate information from the Electronic Control Module (ECM) to other control modules and display modules that are connected to the data link. The ECM broadcasts engine information and diagnostics for the electronic system. This ECM supports the following parameters for the broadcast over the CAN data link:
| Parameters for Data Link Broadcast | ||
| Parameter Name | Parameter Group Number (PGN) | Suspect Parameter Number (SPN) |
| Percent Load | 61443 | 92 |
| Engine Oil Pressure | 65263 | 100 |
| Battery Voltage | 65271 | 168 |
| Boost Pressure | 65270 | 102 |
| Engine Coolant Temperature | 65262 | 110 |
| Fuel Pressure | 65263 | 94 |
| Fuel Rate | 65266 | (1) |
| Engine Speed | 61444 | 190 |
| Engine Hours | 65253 | (1) |
| Throttle Position | 61443 | 91 |
| Atmospheric Pressure | 65269 | 108 |
| Desired Engine Speed | 65247 | 515 |
| Oil Filter Differential Pressure | 65276 | 99 |
| Fuel Filter Differential Pressure | 65276 | 95 |
| Aftercooler Temperature | 65262 | 52 |
| Left Exhaust Temperature | 65176 | 1180 |
| Right Exhaust Temperature | 65176 | 1181 |
| Right Air Filter Restriction | 64976 | 2809 |
| Left Air Filter Restriction | 65270 | 107 |
| Crankcase Pressure | 65263 | 101 |
| Unfiltered Oil Pressure (absolute pressure) | 65170 | 1208 |
| Left Turbocharger Inlet Pressure | 65177 | 1177 |
| Right Turbocharger Inlet Pressure | 65177 | 1176 |
| Startup Mode | 61444 | 1675 |
| Overspeed Test Switch | 65252 | 2812 |
| Air Shutoff | 65252 | 2813 |
| General Alarm Output Status | 65252 | 2814 |
| Inlet Air Temperature | 65270 | 105 |
| Fuel Consumption | 65257 | 250 |
| (1) | No SPN is available at the present time. |
Two 120 Ohm terminating resistors must be installed in the wiring harness in order for the CAN data link to function properly.
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| Illustration 1 | g01227891 |
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Typical schematic for the CAN data link | |
Test Step 1. Inspect the Electrical Connectors and the Wiring
- Remove power from the ECM.
- Thoroughly inspect the ECM connectors J1/P1 and J2/P2. Inspect all of the connectors to other modules on the CAN data link. Refer to the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors" for details.
Show/hide table
Illustration 2 g01233666 P1 ECM connector
(P1-50) CAN data link +
(P1-34) CAN data link −
(P1-42) Shield for the CAN data linkShow/hide table
Illustration 3 g01233672 Customer connector
(Terminal 31) CAN data link +
(Terminal 32) CAN data link −
(Terminal 33) Shield for the CAN data link - Perform a
45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the circuit. - Check the allen head screw for each ECM connector for the proper torque. Refer to Troubleshooting, "Inspecting Electrical Connectors" for the correct torque value.
- Check the harness and the wiring for abrasion and for pinch points.
Expected Result:
All of the connectors, pins and sockets are completely coupled and/or inserted and the harness and wiring are free of corrosion, of abrasion and of pinch points.
Results:
- OK - The harness and connectors appear to be OK. Proceed to Test Step 2.
- Not OK - The connectors and/or wiring are not OK.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.
Verify that the repair eliminates the problem.
STOP
Test Step 2. Verify the Proper Installation of the Terminating Resistors
- Verify that the terminating resistors are installed on the ends of the data link.
- Disconnect J1/P1 ECM connector. Measure the resistance between terminals P1-50 (CAN data link +) and P1-34 (CAN data link -).
Expected Result:
The resistance is approximately 60 ± 3 Ohms.
Results:
- OK - The resistance is within the range. Proceed to Test Step 3.
- Not OK - The resistance is approximately 120 ± 6 Ohms. A terminating resistor is missing or damaged.
Repair: If a termination resistor is missing, install the missing resistor. If both resistors are present, measure the resistance between terminal A and terminal B of the termination resistor. The resistance should measure 120 ± 3 Ohms. Replace the termination resistor if the resistance is not 120 ± 3 Ohms.
STOP
Test Step 3. Check for Shorts in the Harness
- Disconnect ECM connector J1/P1 at the engine ECM.
- Disconnect any control modules from the CAN data link.
- Ensure that Caterpillar Electronic Technician (ET) is not connected to the service tool connector.
- Measure the resistance from terminal P1-50 to every terminal on ECM connectors P1 and P2.
- Measure the resistance from terminal P1-50 to the engine ground stud.
- Measure the resistance from terminal P1-34 to every terminal on ECM connectors P1 and P2.
- Measure the resistance from terminal P1-34 to the engine ground stud.
Expected Result:
The resistance measurements indicate an open circuit.
Results:
- OK - The resistance measurements indicate an open circuit. Proceed to Test Step 4.
- Not OK - The resistance measurements do not indicate an open circuit.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
STOP
Test Step 4. Check for an Open in the Harness
- Use a suitable piece of wire to create a short circuit between the data link wires at one of the control modules on the CAN data link.
- Measure the resistance between terminals P1-50 and P1-34 at the ECM connector.
- Measure the resistance at the connectors of any other control modules.
Expected Result:
The resistance measurement indicates a short circuit.
Results:
- OK - The resistance measurement indicates a short circuit. The CAN data link is OK.
Repair: If the problem is intermittent, perform the diagnostic functional test Troubleshooting, "Inspecting Electrical Connectors".
STOP
- Not OK - The resistance measurement does not indicate a short circuit. There is an open circuit in the harness or connectors.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
STOP