G3520B Engines Caterpillar

The master Electronic Control Module (ECM) supplies 8.0 ± 0.8 VDC to these sensors:

• Sensor for engine coolant pressure (outlet)

• Sensor for inlet air pressure

• Sensor for atmospheric pressure

• The detonation sensors for the left side of the engine

The slave ECM supplies 8.0 ± 0.8 VDC to the detonation sensors for the right side of the engine.

Terminals J1-4, J2-56, and J2-57 are connected together inside the master ECM. A short circuit on one of these terminals will cause a short circuit on the other terminals.

A "+8 V sensor supply" diagnostic code is probably caused by a short circuit or an open circuit in a harness. The next likely cause is a sensor problem. The least likely cause is a problem with an ECM.

Logged diagnostic codes provide a historical record. Before you begin this procedure, use the Caterpillar Electronic Technician (ET) to print the logged codes to a file.

This troubleshooting procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.

Illustration 1	g00993024
Schematic for the 8 V sensors that are powered by the master ECM

Illustration 2	g00993027
Schematic for the 8 volt sensors that are powered by the slave ECM

Test Step 1. Inspect the Electrical Connectors and Wiring.

1. Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.

   Note: For the following steps, refer to Troubleshooting, "Inspecting Electrical Connectors".

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Illustration 3	g00888914
Terminal box for the master ECM (1) J2/P2 connectors for the master ECM (2) J1/P1 connectors for the master ECM (3) J12/P12 connectors for the 8 volt sensors (4) J11/P11 connectors for the detonation sensors on the left side of the engine (5) 16 amp circuit breaker

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Illustration 4	g00901701
Terminal box for the slave ECM (6) J4/P4 connectors for the slave ECM (7) J21/P21 connectors for the detonation sensors on the right side of the engine

2. Thoroughly inspect each of the following connectors:
   • J1/P1 and J2/P2 connectors for the master ECM

   • J12/P12 and J11/P11 connectors on the terminal box for the master ECM

   • J4/P4 connectors for the slave ECM

   • J21/P21 connectors on the terminal box for the slave ECM

   1. Check the torque of the Allen head screw for the ECM connectors. The proper torque is 6 ± 1 N·m (55 ± 9 lb in).
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   Illustration 5	g00980958
   Harness side of the master ECM P1 connector (P1-4) 8 volt supply for the pressure sensors (P1-5) Return for the pressure sensors

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   Illustration 6	g00980959
   Harness side of the master ECM P2 connector (P2-54) Return for the detonation sensors (P2-55) Return for the detonation sensors (P2-56) 8 volt supply for the detonation sensors (P2-57) 8 volt supply for the detonation sensors

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   Illustration 7	g00888905
   Harness side of the P11 connector (P11-A) Return for the detonation sensors (P11-E) Return for the detonation sensors (P11-F) 8 volt supply for the detonation sensors (P1-J) 8 volt supply for the detonation sensors

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   Illustration 8	g00888904
   Harness side of the P12 connector (P12-L) 8 volt supply for the sensors (P12-N) Return

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   Illustration 9	g00980959
   Harness side of the P4 connector for the slave ECM (P4-54) Return for the detonation sensors (P4-55) Return for the detonation sensors (P4-56) 8 volt supply for the detonation sensors (P4-57) 8 volt supply for the detonation sensors

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   Illustration 10	g00888905
   Harness side of the P21 connector (P21-A) Return for the detonation sensors (P21-E) Return for the detonation sensors (P21-F) 8 volt supply for the detonation sensors (P21-J) 8 volt supply for the detonation sensors

   2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit for the 8 volt sensors.
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   Illustration 11	g00901759
   (8) Sensor for engine coolant pressure (outlet) (9) Detonation sensor (10) Sensor for inlet air pressure

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   Illustration 12	g00901765
   (11) Sensor for atmospheric pressure

   3. Check the harness and wiring for abrasion and pinch points from the 8 volt sensors to the electronic control modules.

Expected Result:

All connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points.

Results:

• OK - All connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points. The components are in good condition with proper connections. Proceed to Test Step 2.

• Not OK - At least one of the connectors, pins, and sockets are not connected properly. At least one of the connectors and/or the wiring has corrosion, abrasion, and/or pinch points.

  Repair: Perform the necessary repairs and/or replace parts, if necessary.

  STOP

Test Step 2. Check for Diagnostic Codes

1. Connect Cat ET to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

2. Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.

3. Observe the "Active Diagnostic" screen on Cat ET. Wait at least 30 seconds so that any codes may become activated. Look for these codes:
   • 41-03 8 Volt DC Supply short to +batt

   • 41-04 8 Volt DC Supply short to ground

4. Observe the "Logged Diagnostic" screen on Cat ET. Look for the same codes.

Expected Result:

The 41-03 code or the 41-04 code is not active.

Results:

• No codes - The 41-03 code or the 41-04 code is not active. The 8 volt sensor supply is operating correctly at this time.STOP

• Active code - The 41-03 code or the 41-04 code is active. Proceed to Test Step 3.

• Logged code - The 41-03 code or the 41-04 code is not active. However, there is at least one logged code for the 8 volt sensor supply.

  Repair: There may be a problem with the wiring and/or a connector. Refer to Troubleshooting, "Inspecting Electrical Connectors".

  Verify that the wiring and/or connectors are OK. Check for diagnostic codes again. Proceed to Test Step 3, if necessary.

Test Step 3. Disconnect the 8 Volt Sensors and Look for Active Diagnostic Codes.

1. Turn on the "Active Diagnostic" screen on Cat ET. Verify that the "41-03" or "41-04" code is active.

2. Disconnect each 8 volt sensor one at a time. After you disconnect each sensor, wait for at least 30 seconds and then observe the "Active Diagnostic" screen on Cat ET.

   Note: An "Open Circuit" code will be generated for each sensor that is disconnected. This is normal. Clear the codes after you complete this procedure.

Expected Result:

The original "8 Volt DC Supply" diagnostic code is deactivated when a particular sensor is disconnected.

Results:

• Yes - The original "8 Volt DC Supply" diagnostic code is deactivated when a particular sensor is disconnected. The sensor and/or the wiring for the sensor has a short circuit.

  Repair: Perform the following procedure:

  1. Reconnect the suspect sensor. Verify that the diagnostic code recurs.

  2. Disconnect the suspect sensor. Verify that the diagnostic code is deactivated.

     If these conditions are true, repair the sensor or the sensor's harness. Replace parts, if necessary.

  3. Clear all of the diagnostic codes. Verify that the problem is resolved.

  STOP

• No - The original "8 Volt DC Supply" diagnostic code is still active when a particular sensor is disconnected. Do not reconnect the sensors. Proceed to Test Step 4.

Test Step 4. Isolate the Wiring Harnesses from the Electronic Control Modules

1. Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.

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Illustration 13	g00901907
Harness side of the master ECM P1 and P2 connectors (P1-4) 8 volt supply for the pressure sensors (P2-56) 8 volt supply for the detonation sensors (P2-57) 8 volt supply for the detonation sensors

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Illustration 14	g00901913
Harness side of the P4 connector for the slave ECM (P4-56) 8 volt supply for the detonation sensors (P4-57) 8 volt supply for the detonation sensors

2. If you are troubleshooting an 8 volt problem with the master ECM, use a 151-6320 Wire Removal Tool to remove the wires from the following terminals:
   • (P1-4)

   • (P2-56)

   • (P2-57)

   • (P4-56)

   • (P4-57)

3. If you are troubleshooting an 8 volt problem with the slave ECM, use a 151-6320 Wire Removal Tool to remove the wires from the following terminals:
   • (P4-56)

   • (P4-57)

4. Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.

5. Wait for at least 30 seconds and then observe the "Active Diagnostics" screen on Cat ET. Determine if a 41-03 code or a 41-04 code is active.

Expected Result:

No active codes

Results:

• No codes - The 41-03 code or the 41-04 code is not active. Disconnecting all of the 8 volt wiring from the ECM eliminated the active "8 Volt DC Supply" diagnostic code. There is a problem in a connector and/or the wiring in a harness. Proceed to Test Step 5.

• Active code - There is an active 41-03 or 41-04 code. Disconnecting all of the 8 volt wiring from the ECM did not eliminate the active "8 Volt DC Supply" diagnostic code. There may be a problem with an ECM.

  Repair: Set the engine control to the OFF mode. Switch the 16 amp circuit breaker OFF.Insert all of the terminals that were removed. Pull on the wires in order to verify that the terminals are fully inserted into the connector.It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If the problem is not resolved, perform the following steps:Temporarily install a new ECM. Refer to Troubleshooting, "Replacing the ECM".If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the original ECM. Refer to Troubleshooting, "Replacing the ECM".

  STOP

Test Step 5. Check the Wiring Harnesses on the Left Side of the Engine

1. Set the engine control to the OFF mode. Switch the 16 amp circuit breaker OFF.

2. Insert all of the terminals that were removed. Pull on the wires in order to verify that the terminals are fully inserted into the connector.

3. Disconnect all of the 8 volt sensors.

4. Disconnect the P1 connector and the P2 connector for the master ECM.

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Illustration 15	g00980962
ECM side of the master ECM connectors

Note: For the functions of the terminals, refer to Table 1.

5. Measure the resistance between the terminals that are listed in Table 1.

   During each measurement, wiggle the harnesses in order to check for an intermittent problem. Be sure to wiggle the wires near each of the connectors.

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   Table 1

   Points for the Measurement of Resistance for the Left Side of the Engine
   Connector and Terminal	Connector and Terminal
   P1-4 (8 volt supply)	P1-5 (Digital return)
   	P1-10 (Digital sensor signal)
   	P1-12 (Digital sensor signal)
   	P2-68 (Digital sensor signal)
   P2-56 (8 volt supply)	P2-36 (Detonation sensor signal)
   	P2-37 (Detonation sensor signal)
   	P2-38 (Detonation sensor signal)
   	P2-54 (Digital return)
   P2-57 (8 volt supply)	P2-39 (Detonation sensor signal)
   	P2-44 (Detonation sensor signal)
   	P2-55 (Digital return)
   P1-4 (8 volt supply)	Engine ground
   P2-56
   P2-57
   P1-4	P1-69 (−Battery terminal)
   P2-56
   P2-57
   P1-4	P1-57 (Unswitched +Battery)
   P2-56
   P2-57
   P1-4	P1-70 (Switched +Battery)
   P2-56
   P2-57

Expected Result:

Each check of the resistance is greater than 20,000 ohms.

Results:

• OK - Each check of the resistance is greater than 20,000 ohms. The 8 volt wires and connectors on the left side of the engine do not have a short circuit. Proceed to Test Step 6.

• Not OK - At least one check of the resistance is less than 20,000 ohms. There is a problem with a harness. The problem could be inside the terminal box for the master ECM.

  Repair: Repair the harness, when possible. Replace the harness, if necessary.

  STOP

Test Step 6. Check the Wiring Harnesses on the Right Side of the Engine

1. Disconnect the P3 and P4 connectors.

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Illustration 16	g00980964
ECM side of the connectors for the slave ECM

Note: For the functions of the terminals, refer to Table 1.

2. Measure the resistance between the terminals that are listed in Table 1.

   During each measurement, wiggle the harnesses in order to check for an intermittent problem. Be sure to wiggle the wires near each of the connectors.

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   Table 2

   Points for the Measurement of Resistance for the Right Side of the Engine
   Connector and Terminal	Connector and Terminal
   P4-56 (8 volt supply)	P4-36 (Detonation sensor signal)
   	P4-37 (Detonation sensor signal)
   	P4-38 (Detonation sensor signal)
   	P4-54 (Digital return)
   P4-57 (8 volt supply)	P4-39 (Detonation sensor signal)
   	P4-44 (Detonation sensor signal)
   	P4-55 (Digital return)
   P4-56	Engine ground
   P4-57
   P4-56	P3-69 (−Battery terminal)
   P4-57
   P4-56	P3-57 (Unswitched +battery)
   P4-57
   P4-56	P3-70 (Switched +battery)
   P4-57

Expected Result:

Each check of the resistance is greater than 20,000 ohms.

Results:

• OK - Each check of the resistance is greater than 20,000 ohms. The 8 volt wires and connectors on the right side of the engine do not have a short circuit. The problem seems to be resolved. The initial diagnostic code was probably caused by a poor electrical connection.

  Repair: Reconnect all of the connectors and resume normal operation.

  STOP

• Not OK - At least one check of the resistance is less than 20,000 ohms. There is a problem with a harness on the right side of the engine. The problem could be inside the terminal box for the slave ECM.

  Repair: Repair the harness, when possible. Replace the harness, if necessary.

  STOP