G3500 A3 Engines Caterpillar

The Electronic Control Module (ECM) supplies 8.0 ± 0.8 VDC to the following Pulse Width Modulated sensors (PWM):

• Engine coolant pressure (outlet)

• Air inlet pressure

Note: Excessive pressure can introduce electrical noise in the circuit. This electrical noise may cause a false diagnostic code to be generated.

If the actual inlet manifold air pressure is greater than approximately 338 kPa (49 psi), a 106-08 Air Inlet Pressure Sensor noisy signal may 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 may 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 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. Correct the cause of the original diagnostic code before you continue. Clear the diagnostic codes after the problem is resolved.

Illustration 1	g02225673
Schematic of the circuit for the PWM sensors

Test Step 1. Inspect the Electrical Connectors and the Wiring

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

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

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Illustration 2	g01391862
Locations of the ECM connectors (1) J2/P2 ECM connectors (2) J1/P1 ECM connectors

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Illustration 3	g01391863
Locations of components for the PWM sensors (3) Engine coolant pressure sensor (outlet) (4) Air inlet pressure sensor

2. Thoroughly inspect ECM connectors (1) and (2). Also, thoroughly inspect the connectors for sensors (3) and (4) .

   1. Check the allen head screw for each of the ECM connectors for the proper torque.
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   Illustration 4	g01391854
   Terminal locations at the P1 ECM connector for the PWM sensors (P1-4) +8 VDC (P1-5) Return (P1-10) Engine coolant pressure (outlet)

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   Illustration 5	g01391857
   Terminal locations at the P2 ECM connector for the PWM sensors (P2-65) +8 VDC (P2-66) Return (P2-68) Air inlet pressure

   2. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit for the PWM sensors.

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

Expected Result:

All of 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 Diagnostic Codes that are Related to the 8 VDC Power Supply

1. Establish communication between Caterpillar Electronic Technician (ET) and the ECM. Refer to Troubleshooting, "Electronic Service Tools", if necessary.

2. Observe the "Active Diagnostic" screen on Cat ET. Allow a minimum of 30 seconds for any codes to activate. Look for these codes:
   • 41-3 8 Volt DC Supply voltage above normal

   • 41-4 8 Volt DC Supply voltage below normal

Expected Result:

There are no active codes for the 8 V supply.

Results:

• OK - There are no active codes for the 8 V supply. Proceed to Test Step 3.

• Not OK - There is an active code for the 8 V supply.

  Repair: There is a problem with the 8 V power supply. Refer to Troubleshooting, "+8 V Sensor Voltage Supply" for information that is related to troubleshooting the power supply for these sensors.

  STOP

Test Step 3. Check for Active Diagnostic Codes that are Related to the PWM Sensors

1. Determine if any of these diagnostic codes are active:
   • 106-3 Air Inlet Pressure Sensor voltage above normal

   • 106-4 Air Inlet Pressure Sensor voltage below normal

   • 106-8 Air Inlet Pressure Sensor abnormal frequency, pulse width, or period

   • 109-03 Engine Coolant Outlet Pressure Sensor voltage above normal

   • 109-08 Engine Coolant Outlet Pressure Sensor abnormal frequency, pulse width, or period

Expected Result:

None of the above codes are active.

Results:

• OK - None of the above codes are active.

  Repair: There may be an intermittent electrical problem in the harness or in a connector.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 causing the codes to be logged. Refer to Troubleshooting, "Inspecting Electrical Connectors".

  STOP

• Not OK - At least one of the above diagnostic codes is active. Proceed to Test Step 4.

Test Step 4. Verify the Supply Voltage to the Sensor

1. Disconnect the suspect sensor.

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Illustration 6	g00896288
Harness connector for the PWM sensors (A) 8 V supply or 5 V supply (B) Return

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

Expected Result:

The voltage between terminals A and B is between 7.6 VDC and 8.4 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.

  Repair: There is a problem in the harness between the ECM and the sensor connector. 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. Check the Signal Wire for Battery Voltage

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Illustration 7	g00896299
Harness connector for the PWM sensors (B) Return (C) Signal

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

Expected Result:

The voltage is approximately 6.4 VDC.

Results:

• OK - The voltage is approximately 6.4 VDC. The +Battery voltage is not present on the signal wire. Proceed to Test Step 6.

• Not OK - The voltage is equal to the +Battery voltage. The signal wire is probably shorted to the +Battery between the sensor and the ECM.

  Repair: Set the engine control to the OFF/RESET position. Repair the harness, when possible. Replace the harness, if necessary.

  STOP

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

  Repair: Set the engine control to the OFF/RESET position. Repair the harness, when possible. Replace parts, if necessary.

  STOP

Test Step 6. Check the Signal at the Sensor

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

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

3. Use a multimeter capable of measuring both the duty cycle and the frequency of a signal. Connect the multimeter to terminals B and C of the breakout T.

4. Set the engine control to the COOLDOWN/STOP position.

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.

The frequency is between 400 and 600 Hz.

Results:

• OK - The duty cycle is between 5 percent and 95 percent. The frequency is between 400 and 600 Hz. The sensor is producing a valid signal. 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 or the frequency of the sensor signal is incorrect, set the engine control to the OFF/RESET position.

  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 COOLDOWN/STOP position. 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 ECM

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

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
   Engine coolant pressure (outlet)	J2-68 and J2-66
   Inlet manifold air pressure	J1-10 and J1-5

3. Connect the multimeter to the probes. Use a multimeter capable of measuring both the duty cycle and the frequency of a signal.

4. Set the engine control to the COOLDOWN/STOP position.

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. The frequency is between 400 and 600 Hz.

Results:

• OK - The duty cycle is between 5 percent and 95 percent. 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 COOLDOWN/STOP position.

  2. Check "Status Screen Group 2" on Cat ET. Look for a value from the suspect sensor that is valid.
  The actual air inlet pressure may be below the pressure that can be measured by the sensor at low idle (26.7 kPa (3.87 psi)). This low pressure causes the ECM to set the 106-3 diagnostic code although there is no short circuit to the +Battery side. In this case, adjust the governor in order to make the engine more stable at low idle. Refer to Troubleshooting, "System Configuration Parameters".Otherwise, verify that the ECM is receiving the correct voltage. Refer to Troubleshooting, "Electrical Power Supply".If the condition is not resolved, install a known good ECM according to Troubleshooting, "Replacing the ECM". Verify that the problem is resolved.

  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 ECM. There is a problem in the harness between the sensor and the ECM.

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

  STOP