C13, C15, and C18 Engines Troubleshooting – Electrical Connectors – Inspect

Most electrical faults are caused by poor connections. The following procedure will assist in detecting faults with connectors and with wiring. If a fault is found, correct the condition and verify that the fault is resolved.

Intermittent electrical faults are sometimes resolved by disconnecting and reconnecting connectors. Check for diagnostic codes immediately before you disconnect a connector. Also check for diagnostic codes after you reconnect the connector. If the status of a diagnostic code is changed due to disconnecting and reconnecting a connector, there are several possible reasons. The likely reasons are loose terminals, improperly crimped terminals, moisture, corrosion, and inadequate mating of a connection.

Follow these guidelines:


  • Always use a 1U-5804 Crimp Tool to service Deutsch HD and DT connectors. Never solder the terminals onto the wires. Refer to “SEHS9615, Servicing Deutsch HD, and DT Style Connectors”.
  • Always use a 147-6456 Wedge Removal Tool in order to remove wedges from DT connectors. Never use a screwdriver to pry a wedge from a connector.
  • Always use a breakout harness for a voltmeter probe or a test light. Never break the insulation of a wire in order to access to a circuit for measurements.
  • If a wire is cut, always install a new terminal for the repair.
  • Determine if the problem is intermittent. If the problem is intermittent, attempt to test the circuit before you disconnect any electrical connectors. The test will help identify the root cause of intermittent problems. The “Wiggle Test” on Caterpillar Electronic Technician (ET) may be able to test the circuit. Refer to the documentation that accompanies Cat ET. Perform the wiggle test on the circuit, when possible. Otherwise, continue with this procedure.

Check Connectors for Moisture and Corrosion

Illustration 1 g01131211
Detail A illustrates the incorrect angle of wire entry into the connector. The wire should enter the connector at a perpendicular angle. (typical example)

Inspect all the harnesses. Ensure that the routing of the wiring harness allows the wires to enter the face of each connector at a perpendicular angle. Otherwise, the wire will deform the seal bore. The damaged seal will create a path for the entrance of moisture. Verify that the seals for the wires are sealing correctly.

Illustration 2 g01131276
Diagram for the installation of a connector plug (typical example)

(1) Electronic Control Module (ECM) connector

(2) Correctly inserted plug

(3) Incorrectly inserted plug

Ensure that the sealing plugs are in place. If any of the plugs are missing, replace the plug. Ensure that the plugs are inserted correctly into the connector.

Illustration 3 g01131019
Seal for a three-pin connector (typical example)

Illustration 4 g01131165
Seal for the ECM connector (typical example)

Disconnect the suspect connector and inspect the connector seal. Ensure that the seal is in good condition. If necessary, replace the connector.

Thoroughly inspect the connectors for evidence of moisture entry.

Note: Some minor seal abrasion on connector seals is normal. Minor seal abrasion will not allow the entry of moisture.

If moisture or corrosion is evident in the connector, the source of the moisture entry must be found. The source of the moisture entry must be repaired. If the source of the moisture entry is not repaired, the fault will recur. Simply drying the connector will not fix the fault. Check the following items for the possible moisture entry path:


  • Missing seals 
  • Incorrectly installed seals 
  • Nicks in exposed insulation 
  • Improperly mated connectors 

Moisture can also travel to a connector through the inside of a wire. If moisture is found in a connector, thoroughly check the connector harness for damage. Also check other connectors that share the harness for moisture.

Check the Wires for Damage to the Insulation

Carefully inspect each wire for signs of abrasion, nicks, and cuts.

Inspect the wires for the following conditions:


  • Exposed insulation 
  • Rubbing of a wire against the engine 
  • Rubbing of a wire against a sharp point 

Check all of the fasteners for the harness and the ECM in order to verify that the harness is correctly secured. Also check all of the fasteners in order to verify that the harness is not compressed. Pull back the harness sleeves in order to check for a flattened portion of wire. A fastener that has been overtightened flattens the harness. This damages the wires that are inside the harness.

Inspect the Connector Terminals

Visually inspect each terminal in the connector. Verify that the terminals are not damaged. Verify that the terminals are correctly aligned in the connector and verify that the terminals are correctly located in the connector.

Perform a Pull Test on Each Wire Terminal Connection

Illustration 5 g01131435
Receptacle lock wedge (typical example)

Ensure that the locking wedge for the connector is installed correctly. Terminals cannot be retained inside the connector if the locking wedge is not installed correctly.

Perform the 45 N (10 lb) pull test on each wire. Each terminal and each connector should easily withstand 45 N (10 lb) of tension and each wire should remain in the connector body. This test checks whether the wire was correctly crimped in the terminal and whether the terminal was correctly inserted into the connector.

Check Individual Pin Retention into the Socket

Illustration 6 g01131604
Diagram for testing pin retention (typical example)

Verify that the sockets provide good retention for the pins. Insert a new pin into each socket one at a time in order to check for a good grip on the pin by the socket.

Check the Locking Mechanism of the Connectors
Ensure that the connectors lock correctly. After you lock the connectors, ensure that the two halves cannot be pulled apart.

Verify that the latch tab of the connector is correctly latched. Also verify that the latch tab of the connector returns to the locked position.

Check the Allen Head Screws on the Connectors
Visually inspect the allen head screws for the ECM connectors. Ensure that the threads on each allen head screw are not damaged.

Illustration 7 g01132827
Allen head screw for the 120 pin ECM connector (typical example)

Torque the allen head bolt for the 120 pin ECM connector to 7.0 ± 0.5 N·m (60 ± 4 lb in).

Illustration 8 g01132849
Allen head screw for the 70 pin ECM connector (typical example)

Torque the allen head screw for the 70 pin ECM connector to 6.0 + 1.5 – 1.0 N·m (55 + 13 – 9 lb in).

Illustration 9 g01133047
Allen head screw for the 40 pin customer connector and the 70 pin customer connector (typical example)

Torque the allen head screw for the 40 pin customer connector and the 70 pin customer connector to 2.25 ± 0.25 N·m (20 ± 2 lb in).

Perform the Wiggle Test on the Caterpillar Electronic Technician (ET)
Select the “Wiggle Test” from the diagnostic tests on Cat ET.

Choose the appropriate group of parameters to monitor.

Press the “Start” button. Wiggle the wiring harness in order to reproduce intermittent faults.

If an intermittent fault exists, the status will be highlighted and an audible beep will be heard.

Posted in C18

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