3126B Marine Engines Caterpillar

Use this procedure to troubleshoot any suspect problems with the +8 V digital supply.

This procedure covers the following diagnostic codes:

• 41-03 8 Volt DC Supply short to +batt

• 41-04 8 Volt DC Supply short to ground

The Electronic Control Module (ECM) creates a regulated voltage of 8.0 ± 0.4 VDC that is supplied to terminal A of the harness connector for the coolant level sensor.

A +8 V diagnostic code is probably caused by a short circuit to ground or a short circuit to another voltage source in the harness. The next likely cause is a problem with the sensor. The least likely cause is a problem with the ECM.

Illustration 1	g01094777
Schematic for digital supply

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Turn the keyswitch to the OFF position.
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   Illustration 2	g01147202
   Typical engine view (1) J2/P2 connectors

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   Illustration 3	g01150138
   Typical location of the coolant level sensor (2) Coolant level sensor

2. Thoroughly inspect connectors (1) and (2). Also inspect the wiring from the ECM to the coolant level sensor. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
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   Illustration 4	g01093451
   P2 ECM connector (P2-4) +8 V digital supply (P2-5) Digital sensor return (P2-6) Coolant level sensor

3. Perform a 45 N (10 lb) pull test on each of the wires in the circuit that is associated with the digital sensor supply.

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

5. Check the harness and wiring for abrasions and for pinch points from the sensor to the ECM.

Expected Result:

The harness and the wiring are OK.

Results:

• OK - Proceed to Test Step 2.

• Not OK -

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Verify that all of the seals are properly in place and verify that the connectors are completely coupled.

  Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check for Active Diagnostic Codes

1. Connect Caterpillar Electronic Technician (ET) to the service tool connector.

2. Turn the keyswitch to the ON position.

3. Monitor Cat ET for active diagnostic codes. Check and record any active codes.

   Note: Wait at least 15 seconds in order for the diagnostic codes to become active.

   Check for the following diagnostic codes for the digital supply:

   • 41-03

   • 41-04

Expected Result:

No diagnostic codes that relate to the digital supply are active.

Results:

• OK - No diagnostic code for the digital supply is active. Proceed to Test Step 3 in order to verify that the sensor is receiving the correct supply voltage.

• Not OK - Active 41-03 - A 41-03 diagnostic code is active. Proceed to Test Step 3.

• Not OK - Active 41-04 - A 41-04 diagnostic code is active. Proceed to Test Step 4.

Test Step 3. Check for Supply Voltage at the Sensor's Connector

1. Turn the keyswitch to the OFF position.

2. Disconnect the harness connector for the coolant level sensor.

3. Turn the keyswitch to the ON position.

4. Measure the voltage between terminals A and B at the harness connector.

Expected Result:

The voltage is 8.0 ± 0.4 VDC.

Results:

• OK - The voltage is 8.0 ± 0.4 VDC. The voltage is correct. The problem appears to be resolved.

  Repair: Connect the sensor's connectors. Clear all diagnostic codes. Check for active diagnostic codes. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The voltage is not 8.0 ± 0.4 VDC. The voltage is incorrect. Proceed to Test Step 5.

Test Step 4. Disconnect the +8 V Sensor and Monitor Active Diagnostic Codes

1. Use Cat ET to check for active diagnostic codes. Check and record any active codes.

2. Disconnect the harness connector for the coolant level sensor.

3. Wait for 15 seconds after the sensor is disconnected. Check for an active diagnostic code on Cat ET.

Expected Result:

The 41-04 diagnostic code deactivates when the sensor is disconnected.

Results:

• OK - The 41-04 diagnostic code deactivates when the sensor is disconnected. There may be a problem with the sensor.

  Repair: Connect the sensor and verify that the code recurs. If the code recurs, replace the sensor.

  Return all wiring to the original configuration. Clear all diagnostic codes. Verify that the repair eliminates the problem.

  STOP

• Not OK - The 41-04 diagnostic code stays active when the sensor is disconnected. Leave the sensor disconnected. Proceed to Test Step 5.

Test Step 5. Check the +8 V Supply Wire for a Short Circuit

1. Turn the keyswitch to the OFF position.

2. Disconnect the J1/P1 and J2/P2 ECM connectors.

3. Verify that the coolant level sensor is disconnected.

4. Measure the resistance between the points that are listed in Table 1. Be sure to wiggle the wires in the harnesses as you make each resistance measurement.
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   Table 1

   Resistance Measurements for the Wiring Harness
   Connector and Terminal	Terminal
   P2-4 (+ 8 VDC)	All of the other terminals on the P2 connector
   	All of the terminals on the P1 connector
   	Engine ground

Expected Result:

All of the resistance measurements indicate an open circuit.

Results:

• OK - All of the resistance measurements indicate an open circuit. Proceed to Test Step 6.

• Not OK - At least one resistance measurement does not indicate an open circuit. There is a short circuit in a wiring harness. There may be a problem with a connector.

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

  STOP

Test Step 6. Check the +8 V Supply and the Sensor Common for an Open Circuit

1. Use a jumper wire to create a short circuit between terminals P2-4 (+8 VDC) and P2-5 (return).

   Note: Wiggle the harness during the following measurements in order to reveal any intermittent short condition.

2. Measure the resistance between terminals A and B at the harness connector for the coolant level sensor.

3. Remove the jumper wire.

Expected Result:

The resistance is less than ten Ohms.

Results:

• OK - The resistance is less than ten Ohms. The circuit is not open. Proceed to Test Step 7.

• Not OK - The resistance is greater than ten Ohms. The +8 V supply wire or the sensor common has excessive resistance. There may be a problem in a connector.

  Repair: Repair the wire and/or the connector, when possible. Replace parts, if necessary. Verify that the problem is resolved.

  STOP

Test Step 7. Check the +8 V Supply at the ECM

1. Remove the terminal from location P2-4. Install a jumper wire into the connector at location P2-4.

2. Remove the terminal from location P2-5. Install a jumper wire into the connector at location P2-5.

3. Turn the keyswitch to the ON position.

4. Measure the voltage between the jumper wires.

5. Turn the keyswitch to the OFF position.

6. Return the wiring to the original configuration.

Expected Result:

The voltage is 8.0 ± 0.4 VDC.

Results:

• OK - The voltage is 8.0 ± 0.4 VDC. The problem appears to be resolved.

  Repair: Clear all diagnostic codes. Check for active diagnostic codes. If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The voltage is not 8.0 ± 0.4 VDC. The voltage is incorrect.

  Repair: Replace the ECM. Refer to Troubleshooting, "Replacing the ECM".

  STOP