C13, C15, and C18 Tier 4 Interim Engines Caterpillar

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

Note: Some of the following codes may not be applicable for certain applications.

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

1. Turn the keyswitch to the OFF position.

2. Thoroughly inspect the connectors that are associated with the data link circuits. Refer to Troubleshooting, "Electrical Connectors - Inspect".

3. Disconnect the P1 and the P2 ECM connector.

4. Disconnect Cat ET from the service tool connector.

5. 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.
   Show/hide table

   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. -

  Repair: Repair the connectors and/or the wiring. Replace parts, if necessary. Verify that the original problem is resolved.

  STOP

Test Step 2. Check for an Open Circuit

1. 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.

2. Measure the resistance between P1-50 (CAN data link +) and P1-34 (CAN data link +).

3. Fabricate a jumper wire that is long enough to create a test circuit across two terminals. Use the jumper wire in order to create a short circuit between terminals 23 (CAN data link +) and 24 (CAN data link −) on the Clean Emissions Module (CEM) connector.

4. Measure the resistance between P2-12 (CAN data link +) and P2-11 (CAN data link −).

Results:

• Each check of the resistance indicates a short circuit. - Remove the jumper wire from the service tool connector. Proceed to Test Step 3.

• 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. Verify that the problem is resolved.

  STOP

Test Step 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.

1. At the service tool connector, measure the resistance between the terminals for the CAN data link.

Results:

• The resistance is between 45 Ohms and 75 Ohms. The termination resistors are OK. - The data link appears to be OK. There is an intermittent problem in a connector or in the harness. Repair the problem.

• 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.

  STOP

• 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.

  STOP