C15 and C18 Engines for Caterpillar Built Machines Caterpillar

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

Table 1

Diagnostic Codes Table
CDL Code	Code Description	Comments
246-9	Proprietary CAN Data Link : Abnormal Update Rate	The Electronic Control Module (ECM) has lost communications over the CAN data link. The code is logged. The check engine lamp is illuminated.
247-9	SAE J1939 Data Link : Abnormal Update Rate	The ECM has lost all communications over the global CAN data link. The code is logged. The check engine lamp is illuminated.
248-9	Cat Data Link not communicating	The ECM has lost all communications with the transmission over the Cat Data Link. The code is logged. The check engine lamp is illuminated.
296-9	Transmission Control : Abnormal Update Rate	The ECM has lost all communications with the transmission. The code is logged. The check engine lamp is illuminated.
533-9	Brake Control : Abnormal Update Rate	The ECM has lost all communications with brake control. The code is logged. The check engine lamp is illuminated.
1273-9	Chassis Control Module : Abnormal Update Rate	The ECM has lost all communications with the chassis control module over the Cat Data Link. The code is logged. The check engine lamp is illuminated.
1639-2	Machine Security System Module : Erratic, Intermittent, or Incorrect	The ECM has lost communications with the Machine Security System Module (MSSM) over the Cat Data Link. The code is logged. The check engine lamp is illuminated.
1639-9	Machine Security System Module : Abnormal Update Rate	The ECM has lost all communications with the Cat Monitoring System over the Cat Data Link. The code is logged. The check engine lamp is illuminated.

Note: If a 1639-2 diagnostic code is active, verify that the following information is correct before proceeding with this procedure:

• The part number of the flash software for the Machine ECM

• The part number of the flash software for the Machine Security System ECM

• The part number of the Machine ECM

• The part number of the Machine Security System ECM

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	g03500363
Schematic for the Cat 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

Table 2

Troubleshooting Test Steps	Values	Results
1. Verify the Proper Installation of the Data Link Circuit A. Turn the keyswitch to the OFF position. B. Disconnect the P1 ECM connector. C. Measure the resistance between P1-50 and P1-34.	Resistance	Result: The resistance is between 57 ohms and 63 ohms and a -9 code is logged. Check the power supply and ground to the module and all ECMs on the Can Data Link and the Cat Data Link that pertain to the -9 code that is logged or active. Power loss to any control module will generate a -9 code. Refer to the electrical schematic for details. Result: The resistance is between 114 ohms and 126 ohms. A terminating resistor is missing. Verify that two terminating resistors exist on the data link. One resistor must be located on each end of the data link. The engine is shipped with one terminating resistor that is installed between the ECM and the customer connector. Refer to the electrical schematic to determine the missing resistor. Replace the missing resistor and verify that the repair eliminates the problem. Result: The resistance is less than 57 ohms. Proceed to Test Step 2. Result: The resistance is greater than 126 ohms. Proceed to Test Step 3.

Table 3

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 4

Troubleshooting Test Steps	Values	Results
2. 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 P1 ECM connector. D. Disconnect Cat ET from the service tool connector. E. Remove the terminating resistors from the CAN Data Link circuit. F. Disconnect the J1939 display if equipped. G. Measure the resistance between the points that are listed in Table 3. Be sure to wiggle the wires in the harnesses as you make each resistance measurement.	Resistance	Result: The resistance is greater than 20,000 ohms. Proceed to Test Step 3 Result: The resistance is less than 20,000 ohms. Repair the connectors and/or the wiring. Replace parts, if necessary. Verify that the original problem is resolved.
3. Check for an Open Circuit A. Fabricate a jumper wire that is long enough to create a test circuit across two terminals. Create a short circuit between terminals D (Cat Data Link +) and E (Cat Data Link −) on the service tool connector. B. Measure the resistance between P1-8 (Cat Data Link +) and P1-9 (Cat Data Link −). C. Fabricate a jumper wire that is long enough to create a test circuit across two terminals. Create a short circuit between terminals G (CAN data link +) and F (CAN data link −) on the service tool connector. D. Measure the resistance between P1-50 (Cat Data Link +) and P1-34 (Cat Data Link −).	Resistance	Result: At least one of the resistance measurements indicates an open circuit. Remove the jumper wire from the ECM connector. Determine the cause of the open circuit. Repair the problem, when possible. Replace parts, if necessary. Verify that the problem is resolved.

Complete the procedure in the order in which the steps are listed.

If the procedure corrected the issue, return the engine to service.

If the procedure did not correct the issue, Contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).