3126B and 3126E On-highway Engines Caterpillar

Use this procedure under the following situation:

Use this procedure if Caterpillar Electronic Technician (ET) will not power up. Also, use this procedure if Cat ET will not communicate with the Engine Control Module (ECM) through the data link connector.

The following background information is related to this procedure:

The ATA data link (American Trucking Association) is the standard for data link communications that is used by the ECM to communicate with electronic service tools. The SAE specification J1587 defines the format of the messages and data that is being communicated. The SAE specification J1708 defines the hardware requirements and the protocol of the serial communications. Some electronic dashboards use this data link to receive information. Some automatic transmissions also receive information from this data link.

The ECM provides the following two terminals at the J1 ECM connector for the ATA data link:

• Terminal 8 (J1587 Data Link Positive)

• Terminal 9 (J1587 Data Link Negative)

The vehicle OEM provides twisted pair wiring from the ECM to the data link connector.

Remember that there are potentially several devices that are installed in the vehicle and remember that these devices are connected to the ATA data link at one time. These devices include dash displays, trip recorders and transmission controls. These devices may cause problems with the data link. These problems can disrupt communications to the ECM and from the ECM.

Communication

When the keyswitch is in the OFF position, the ECM may communicate with Cat ET. The communications may be disrupted and the communications may require frequent reconnection. In order to avoid this problem, place the engine control in the ON mode when Cat ET is being used.

Cat ET may indicate 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 will indicate that the latest version of Cat ET has not been installed or this message will indicate that the software in the ECM is newer than the software for Cat ET.

Illustration 1	g00650338
Schematic for ATA Data Link with 6-pin connector

Test Step 1. Inspect the Electrical Connectors And the Wiring

1. Turn the keyswitch to the OFF position.

Show/hide table



Illustration 2	g01146374

2. Thoroughly inspect connector (1).

   Also inspect the following electrical connectors:

   • Cab data link connector

   • Firewall bulkhead connector

   • Service tool connectors

   • ATA data link (terminal 8 and terminal 9) in the connectors

   Refer to Troubleshooting, "Electrical Connectors -Inspect" for details.

Show/hide table



Illustration 3	g01104200
P1 ECM connector (P1-8) J1587 Data Link + (P1-9) J1587 Data Link −

Show/hide table



Illustration 4	g00650354
Data link connectors

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector that are associated with the ATA data link.

4. Check the allen head screw on each ECM connector for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque value.

5. Check the harness and wiring for abrasion and for pinch points from the connector to the ECM.

Expected Result:

All connectors, pins and sockets are completely coupled and/or inserted and the harness and wiring are free of corrosion, of abrasion or of pinch points.

Results:

• OK - The harness and connectors appear to be OK. Proceed to Test Step 2.

• Not OK - There is a problem with the connectors and/or wiring.

  Repair: Perform the following 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. Determine the Nature of the Problem

1. Connect Cat ET to the data link connector.

2. Start the engine.

Expected Result:

The engine starts. Cat ET powers up and Cat ET communicates without error.

Note: Check the display screen or check the communication adapter display in order to determine if Cat ET has powered up. Cat ET will display information that shows if the tool is receiving power. If Cat ET or the communication adapter powers up, the data link connector is receiving power.

Results:

• OK - There is not a problem with the ATA data link at this time. If an intermittent condition exists, thoroughly inspect all wiring and connectors.

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Electrical Connectors - Inspect"

  STOP

• Not OK - Cat ET displays an error message. The ECM is receiving battery power. Proceed to Test Step 5.

• Not OK - The engine cranks but the engine will not start.

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Engine Cranks But Will Not Start"

  STOP

• Not OK - The engine will not crank.

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Engine Will Not Crank"

  STOP

• Not OK - Cat ET does not power up or the communications adapter does not power up. Ensure that the ECM is receiving the correct battery power. Proceed to Test Step 3.

Test Step 3. Check the Battery Supply Voltage to the Cab Data Link Connector

1. Turn the keyswitch to the ON position.

2. Use a multimeter in order to measure the voltage from the +Battery to the −Battery of the cab data link connector.

   Refer to Illustration 4.

Expected Result:

The voltage is between 11.0 and 13.5 VDC for a 12 Volt system or between 22.0 and 27.0 VDC for a 24 Volt system.

Results:

• OK - The cab data link connector is currently receiving the correct voltage. Proceed to Test Step 4.

• Not OK - The cab data link connector is not receiving the correct voltage.

  Repair: Inspect the wiring and fuses to the connector. Repair the wiring or batteries and/or replace the wiring or batteries, as required. Send the vehicle to the OEM dealer for repair, if necessary. Verify that the repair eliminates the problem.

  STOP

Test Step 4. Check Cat ET on Another Engine

1. If another engine is available with an ECM, connect ET to the other vehicle by using the same cables.

2. Turn the keyswitch to the ON position. Determine if Cat ET communicates correctly with the other engine.

3. If another engine is not available in the shop, find a different set of the electronic service tool cables. Ensure that the set of cables is a complete set.

4. Use the other cables or use new cables in order to connect Cat ET to the data link connector.

5. Turn the keyswitch to the ON position.

6. If changing cables allows Cat ET to communicate properly, use the following procedure:

   1. Turn the keyswitch to the OFF position.

   2. Replace the pieces from the old set of cables into the new set of cables that is able to communicate with the ECM. Replace one cable at a time.

   3. Power Cat ET after each of the pieces is replaced. Use this method to find the faulty piece.

7. If changing cables does not allow Cat ET to communicate properly, connect another electronic service tool to the engine.

8. Turn the keyswitch to the ON position.

Expected Result:

Cat ET is communicating correctly with a different engine. Cat ET will not communicate with the original ECM.

Results:

• OK - Cat ET seems to be communicating correctly. Proceed to Test Step 5.

• Not OK - Installing a different service tool allows Cat ET to communicate correctly. The original electronic service tool is faulty.

  Repair: Send the faulty electronic service tool for repairs.

  STOP

Test Step 5. Check the Battery Voltage at the ECM

Illustration 5	g01152362
ECM breakout T-connector and terminal locations for ECM P1 (52) Unswitched +Battery (53) Unswitched +Battery (65) -Battery (67) -Battery (70) Keyswitch

1. Turn the ignition key switch to the OFF position.

2. Ensure that Cat ET is connected to the data link connector.

3. Disconnect the J1/P1 ECM connector and insert a breakout T.

4. Turn the keyswitch to the ON position.

5. Measure the voltage between P1-52 (unswitched +Battery) and P1-65 (− Battery).

6. Measure the voltage between P1-53 (unswitched +Battery) and P1-67 (− Battery).

7. Measure the voltage between P1-70 (keyswitch) and terminal P1-65 (− Battery). Measure the voltage between P1-70 (switched +Battery) and P1-67 (− Battery).

Expected Result:

The voltage is between 11.0 and 13.5 VDC for a 12 volt system or between 22.0 and 27.0 VDC for a 24 volt system.

Results:

• OK - The ECM is currently receiving the correct voltage. Proceed to Test Step 6.

• Not OK - The ECM is not receiving the correct voltage. Ensure that there is not an aftermarket engine protection switch that is overriding battery power to the ECM.

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Ignition Key Switch Circuit and Battery Supply Circuit - Test"

  STOP

Test Step 6. Connect Cat ET Directly to the ECM

Illustration 6	g00741090

Show/hide table

Batteries give off flammable fumes which can explode. To avoid injury or death, do not strike a match, cause a spark, or smoke in the vicinity of a battery.

Show/hide table

NOTICE
Do not connect the bypass harness to the battery until the 20 Amp in-line fuse has been removed from the +Battery line. If the fuse is not removed before connection to the battery a spark may result.

1. Turn the keyswitch to the ON position.

2. Disconnect the J1/P1 (ECM connectors).

3. Install an electronic service tool power bypass cable. Connect a bypass harness to ECM connector J1.

   Refer to Illustration 6 for the bypass harness.

   Note: This bypass directly connects the circuit for the keyswitch to the ECM. The ECM will remain powered until the connection to the unswitched +Battery is disconnected. Remove the 20 Amp fuse from the in-line fuse holder to power down the ECM. Do not connect the bypass to the battery posts without first removing the 20 Amp in-line fuse or do not remove the bypass from the battery posts without first removing the 20 Amp in-line fuse.

Expected Result:

Cat ET is operating correctly.

Results:

• OK - Cat ET is operating correctly.

  Repair: Perform the following repair:There is a problem in the vehicle wiring, or another device in the vehicle is causing problems on the data link. Either determine the device that is causing the problem or send the vehicle to the OEM dealer for repair.Verify that the repair eliminates the problem.

  STOP

• Not OK - Verify that the 20 Amp fuse in the bypass harness of Cat ET is not open. A fuse that is open is a blown fuse. Proceed to Test Step 7.

Test Step 7. Connect Cat ET and the ECM to Another Battery

Show/hide table

Batteries give off flammable fumes which can explode. To avoid injury or death, do not strike a match, cause a spark, or smoke in the vicinity of a battery.

Show/hide table

NOTICE
Do not connect the bypass harness to the battery until all of the in-line fuses have been removed from the +Battery line. If the fuses are not removed before connection to the battery a spark may result.

1. Connect the battery wires from the bypass harness of Cat ET to a different battery that is not on the vehicle.

Expected Result:

Cat ET is operating correctly.

Results:

• OK - The vehicle battery is causing the problem.

  Repair: Perform the following diagnostic procedure:Troubleshooting, "Ignition Key Switch Circuit and Battery Supply Circuit - Test"

  STOP

• Not OK -

  Repair: Perform the following repair:

  1. Temporarily connect a test ECM.

  2. Remove all jumpers and replace all connectors.

  3. Recheck the system for active diagnostic codes.

  4. Repeat the test step.

  5. If the problem is resolved with the test ECM, reconnect the suspect ECM.

  6. If the problem returns with the suspect ECM, replace the ECM.

  7. Verify that the repair eliminates the problem.

  STOP