C27 and C32 Engines for Caterpillar Built Machines Caterpillar

Data Link - Test

Usage:

990K A9P

Use this procedure to troubleshoot the electrical system if a problem is suspected with the CAN data link or the Cat Data Link, or if a diagnostic code in Table 1 is active or easily repeated.

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Table 1
CDL Code	Code Description	Comments
296-9	Transmission Control : Abnormal Update Rate	The Electronic Control Module (ECM) has lost all communications with the transmission ECM over the Cat Data Link. The code is logged. The check engine lamp is illuminated.
596-9	Implement Control : Abnormal Update Rate	The ECM has lost all communications with the implement ECM over the Cat Data Link. The code is logged. The check engine lamp is illuminated.

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.

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Illustration 1	g02138795
Schematic for the Cat Data Link

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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 +

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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

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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
P1-8 (Cat Data Link +)	Negative ground
P1-9 (Cat Data Link -)	All of the other terminals on the P1 connector
P1-9 (Cat Data Link -)	Negative ground
P1-50 (CAN data link +)	All of the other terminals on the P1 connector
P1-50 (CAN data link +)	Negative ground
P1-34 (CAN data link -)	All of the other terminals on the P1 connector
P1-34 (CAN data link -)	Negative ground

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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 is long enough to create a test circuit across two terminals at the harness connector. Crimp connector sockets to each end of the jumper wire. B. Use the jumper wire in order to create a short circuit between terminals D (Cat Data Link +) and E (Cat Data Link −) on the service tool connector. C. Measure the resistance between P1-8 (Cat Data Link +) and P1-9 (Cat Data Link −). D. Use the jumper wire in order to create a short circuit between terminals G (CAN data link +) and F (CAN data link −) on the service tool connector. E. Measure the resistance between P1-50 (Cat Data Link +) and P1-34 (Cat Data Link −).	Short Circuit	Result: Each of the resistance measurements indicate a short circuit. Remove the jumper wire from the service tool connector. Proceed to Test Step 3. Result: At least one of the resistance measurements indicates an open circuit. Repair: Remove the jumper wire from the ECM connector. Determine the cause of the open circuit. Repair the problem, when possible. Replace parts, if necessary. If the problem is not resolved, proceed to Test Step 3.
Troubleshooting Test Steps	Values	Results
3. Check the Termination Resistors for the CAN Data Link Note: Perform this test only if you are troubleshooting a problem with the CAN data link. A. At the service tool connector, measure the resistance between the terminals for the CAN data link.	Resistance between 45 Ohms and 75 Ohms	Result: The resistance is between 45 Ohms and 75 Ohms. Repair: The termination resistors are OK. The data link appears to be OK. The problem is probably an intermittent problem in a connector or in the harness. If the problem persists, perform this test procedure again. If an intermittent problem is suspected, refer to Troubleshooting, "Electrical Connectors - Inspect" for information that is related to troubleshooting intermittent electrical problems. Verify that the repair has eliminated the problem. Result: The resistance is approximately 120 Ohms. There is a problem with a termination resistor. At least one measurement is less than five Ohms. The wiring for a data link has a short circuit. Repair: Determine the cause of the missing termination resistor. Repair the problem, when possible. Replace parts, if necessary. Verify that the problem is resolved. Verify that the repair has eliminated the problem. Result: The resistance is greater than 140 ohms. There is a problem with both termination resistors. Repair: Determine the cause of the problem. Repair the problem, when possible. Replace parts, if necessary. Verify that the problem is resolved. Verify that the repair has eliminated the problem.