G3520B Industrial Engine Caterpillar

The G3520B Engine contains the following Pulse Width Modulated sensors (PWM):

• Engine coolant pressure (outlet)

• Boost pressure

• Inlet manifold air pressure

• Atmospheric pressure

• Humidity

A PWM sensor produces a digital signal. In a digital signal, the duty cycle varies as the input condition changes. The frequency remains constant. Refer to Illustration 1.

Illustration 1	g00852792
Sample duty cycles that are low, medium, and high.

The master ECM supplies 8.0 ± 0.8 VDC to these sensors: engine coolant pressure (outlet), inlet manifold air pressure and atmospheric pressure. The master ECM supplies 5.0 ± 0.5 VDC to the humidity sensor.

Note: Excessive pressure can generate false "noisy signal" diagnostic codes.

If the actual inlet manifold air pressure is greater than approximately 338 kPa (49 psi), a "106-08 Air Inlet Pressure Sensor noisy signal" diagnostic code will be generated. Although there is not a problem with the sensor, the code will be generated.

If the actual engine coolant pressure is greater than approximately 444 kPa (64 psi), a "109-08 Engine Coolant Outlet Pressure Sensor noisy signal" diagnostic code will be generated. Although there is not a problem with the sensor, the code will be generated.

If a "106-08" or "109-08" diagnostic code is generated, measure the absolute pressure with a pressure gauge before you troubleshoot the sensor. If the pressure is actually too high, reduce the pressure in order to avoid activation of false diagnostic codes.

Logged diagnostic codes provide a historical record. Before you begin this procedure, 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 2	g01090394
Schematic of the circuits for the PWM sensors

Test Step 1. Inspect the Electrical Connectors and Wiring

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

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

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Illustration 3	g01090415
Terminal box for the master ECM (1) J2/P2 connectors for the master ECM (2) J1/P1 connectors for the master ECM (3) J7/P7 connectors for the harness to the PWM sensors

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

   • J7/P7 connectors on the terminal box

   • The connectors for each PWM sensor

   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 4	g00995419
   Harness side of the master ECM P1 connector (P1-2) 5 volt supply (P1-3) Return (P1-4) 8 volt supply (P1-5) Return (P1-10) Signal for inlet manifold air pressure (P1-11) Signal for humidity (P1-12) Signal for atmospheric pressure

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   Illustration 5	g00995459
   Harness side of the master ECM P2 connector (P2-68) Signal for engine coolant pressure (outlet) (P2-70) Signal for boost pressure

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   Illustration 6	g01090422
   Harness side of the P7 connector (P7-I) Signal from the humidity sensor (P7-X) Signal from the boost pressure sensor (P7-Y) Signal from the atmospheric pressure sensor (P7-c) Signal from the engine coolant pressure sensor (P7-e) Signal from the inlet air pressure sensor

   2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the signals from the PWM sensors.
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   Illustration 7	g01090452
   Left side view (4) Boost pressure sensor (5) Humidity sensor (6) Sensor for atmospheric pressure (7) Sensor for engine coolant pressure (outlet) (8) Sensor for inlet air pressure

   3. Check the harness and wiring for abrasion and for pinch points from each PWM sensor to the master ECM.

Expected Result:

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

Results:

• OK - The components are in good condition with proper connections. Proceed to Test Step 2.

• Not OK - The components are not in good condition and/or at least one connection is improper.

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

  Stop.

Test Step 2. Check for Active "8 Volt DC Supply" Diagnostic Codes and "5 Volt Sensor DC Supply" Diagnostic Codes

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

2. Restore the electrical power to the engine. Set the engine control to the STOP mode.

3. Observe the "Active Diagnostic" screen on Cat ET. Allow a minimum of thirty seconds for any codes to activate. Look for these codes:
   • 41-03 8 Volt DC Supply short to +batt

   • 41-04 8 Volt DC Supply short to ground

   • 262-03 5 Volt Sensor DC Supply short to +batt

   • 262-04 5 volt Sensor DC Supply short to ground

Expected Result:

There are no active "8 Volt DC Supply" diagnostic codes or "5 Volt Sensor DC Supply" diagnostic codes.

Results:

• No codes - There are no active diagnostic codes for the power supplies. Proceed to Test Step 3.

• Active code - There is an active diagnostic code for a power supply. This procedure will not work when this type of code is active.

  Repair: Refer to Troubleshooting, "+8 V Sensor Voltage Supply", or Troubleshooting, "+5 V Sensor Voltage Supply".

  Stop.

Test Step 3. Check for Active Diagnostic Codes for the PWM Sensors

1. Turn on the "Active Diagnostic" screen on Cat ET. Determine if any of these diagnostic codes are active:
   • 102-03 Boost Pressure Sensor short to +batt

   • 102-08 Boost Pressure Sensor noisy signal

   • 106-03 Air Inlet Pressure Sensor open/short to +batt

   • 106-08 Air Inlet Pressure Sensor noisy signal

   • 109-03 Engine Coolant Outlet Pressure open/short to +batt

   • 109-08 Engine Coolant Outlet Pressure noisy signal

   • 1758-03 Specific Humidity Sensor open/short to +batt

   • 1758-08 Specific Humidity Sensor noisy signal

   • 1759-03 Exhaust Back Pressure Sensor open/short to +batt

   • 1759-08 Exhaust Back Pressure Sensor noisy signal

Expected Result:

One of the above codes is active.

Results:

• Yes - At least one of the above diagnostic codes is active. Proceed to Test Step 4.

• No - None of the above codes are active.

  Repair: If any of the above codes are logged and the engine is not running properly, refer to Troubleshooting, "Troubleshooting Without a Diagnostic Code".If the engine is running properly at this time, there may be an intermittent problem in the harness that is causing the codes to be logged. Refer to Troubleshooting, "Inspecting Electrical Connectors".

  Stop.

Test Step 4. Verify the Supply Voltage to the Sensor

1. Set the engine control to the OFF/RESET mode.

2. Disconnect the suspect sensor.

3. Set the engine control to the STOP mode.

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Illustration 8	g00896288
Harness connector for the PWM sensors (A) 8 volt supply or 5 volt supply (B) Return

4. At the harness connector for the suspect sensor, measure the voltage between terminals A and B.

Expected Result:

The voltage is between 7.6 VDC and 8.4 VDC. If you are troubleshooting the humidity sensor, the voltage is between 4.5 VDC and 5.5 VDC.

Results:

• OK - The voltage is within the specification. The correct voltage is present at the sensor connector. Proceed to Test Step 5.

• Not OK - The voltage is not within the specification. The correct voltage is not present at the sensor connector. The correct voltage must be present at the sensor connector in order to continue this procedure. The wiring problem may be inside the terminal box, or in the engine harness.

  Repair: Verify that the wiring and/or connectors are OK. Repair any faulty wiring and/or connectors, when possible. Replace any faulty wiring and/or connectors, if necessary. Refer to Troubleshooting, "Inspecting Electrical Connectors".

  Stop.

Test Step 5. Verify that +Battery Voltage is Not Present in the Signal Wire

1. At the harness connector for the suspect sensor, measure the voltage between terminals B and C.

Expected Result:

The voltage is between 7.0 VDC and 8.0 VDC.

Results:

• OK - The voltage is between 7.0 VDC and 8.0 VDC. The battery voltage is not present in the signal wire. Proceed to Test Step 6.

• Not OK - The voltage is approximately equal to the battery voltage. The signal wire is probably shorted to the battery between the sensor and the master ECM.

  Repair: Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine. Repair the harness, when possible. Replace the harness, if necessary.

  Stop.

• Not OK - The voltage is approximately 0 volts. The signal wire is probably shorted to ground between the sensor and the master ECM.

  Repair: Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine. Repair the harness, when possible. Replace the harness, if necessary.

  Stop.

Test Step 6. Check the Signal at the Sensor

1. Set the engine control to the OFF/RESET mode.

2. Install a 8T-8726 Adapter Cable As (Three-Pin Breakout) at the harness connector for the suspect sensor.

3. Connect a multimeter to terminals B and C of the breakout t.

4. Set the engine control to the STOP mode.

5. Measure the duty cycle and the frequency of the suspect sensor.

Expected Result:

The duty cycle is between 5 percent and 95 percent for the boost pressure sensor, for the engine coolant pressure sensor, for the inlet manifold pressure sensor, or for the atmospheric pressure sensor. The duty cycle is between 10 and 90 percent for the humidity sensor.

The frequency is between 400 and 600 Hz.

Results:

• OK - The duty cycle is between 5 percent and 95 percent for the boost pressure sensor, for the engine coolant pressure sensor, for the inlet manifold pressure sensor, or for the atmospheric pressure sensor. The duty cycle is between 10 and 90 percent for the humidity sensor. The frequency is between 400 and 600 Hz. A valid signal is produced by the sensor. Proceed to Test Step 7.

• Not OK - The duty cycle or the frequency is incorrect. The sensor is receiving the correct supply voltage but the sensor is not producing a valid signal.

  Repair: Perform the following steps:

  1. Thoroughly inspect the connector for the sensor according to Troubleshooting, "Inspecting Electrical Connectors".

  2. Check the duty cycle and the frequency of the sensor signal again.

  3. If the duty cycle and the frequency of the sensor signal are incorrect, set the engine control to the OFF/RESET mode.

  4. Disconnect the sensor. Connect a sensor that is known to be good. Do not install the new sensor into the engine yet.

  5. Set the engine control to the STOP mode. Allow a minimum of 30 seconds for any codes to activate.

  6. Check for an active diagnostic code. If the code is not active for the new sensor, install the sensor into the engine. Clear any logged diagnostic codes.

  Stop.

Test Step 7. Check the Signal at the Master ECM

1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

2. Insert two 7X-1710 Multimeter Probes into the terminals that are appropriate for the suspect sensor.

   The terminals for the connection of the probes are identified in Table 1.

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   Table 1

   Terminals for the Connection of the Probes
   Suspect Sensor	Connector and Terminals
   Boost pressure	J2-70 and J1-5
   Engine coolant pressure (outlet)	J2-68 and J1-5
   Inlet manifold air pressure	J1-10 and J1-5
   Atmospheric pressure	J1-12 and J1-5
   Humidity	J1-11 and J1-3

3. Connect the multimeter to the probes.

4. Restore the electrical power to the engine. Set the engine control to the STOP mode.

5. Measure the duty cycle and the frequency of the signal from the suspect sensor.

Expected Result:

The duty cycle is between 5 percent and 95 percent for the engine coolant pressure sensor, for the inlet manifold pressure sensor, or for the atmospheric pressure sensor. The duty cycle is between 10 and 90 percent for the humidity sensor.

The frequency is between 400 and 600 Hz.

Results:

• OK - The duty cycle is between 5 percent and 95 percent for the engine coolant pressure sensor, for the inlet manifold pressure sensor, or for the atmospheric pressure sensor. The duty cycle is between 10 and 90 percent for the humidity sensor. The frequency is between 400 and 600 Hz. The ECM is receiving a valid signal from the sensor.

  Repair: Perform the following steps:

  1. Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.

  2. Disconnect the probes from the ECM connector.

  3. Restore the electrical power to the engine. Set the engine control to the STOP mode.

  4. Check "Status Screen Group 2" on Cat ET. Look for a valid signal.
  It is possible that the actual air inlet pressure is less than the pressure that can be measured by the sensor during low idle operation (26.7 kPa (3.87 psi)). This causes the master ECM to set the 106-03 diagnostic code although there is no short circuit to the +battery side. In this case, adjust the derivative gain and the fuel quality in order to make the engine more stable at low idle. Refer to Troubleshooting, "System Configuration Parameters".Otherwise, verify that the master ECM is receiving the correct voltage. Refer to Troubleshooting, "Electrical Power Supply".If the condition is not resolved, temporarily install a new master 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.

• Not OK - The duty cycle or the frequency is incorrect. The sensor is producing a valid signal but the signal does not reach the master ECM. There is a problem in the harness between the sensor and the master ECM.

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

  Stop.