The engine contains the following Pulse Width Modulated sensors (PWM):
- Engine coolant pressure (outlet)
- Air inlet pressure
This procedure covers the following diagnostic codes:
- 106-3 Air Inlet Pressure Sensor : Voltage Above Normal
- 106-4 Air Inlet Pressure Sensor : Voltage Below Normal
- 109-3 Engine Coolant Outlet Pressure Sensor : Voltage Above Normal
- 109-8 Engine Coolant Outlet Pressure Sensor : Abnormal Frequency, Pulse Width, or Period
Note: The air inlet pressure sensor may be a PWM sensor or an analog sensor. Determine the type of sensor before you use this procedure. The air inlet pressure sensor is a PWM sensor if a wire is installed in P1-10. Use this procedure if the air inlet pressure sensor is a PWM sensor. The air inlet pressure sensor is an analog sensor if a wire is installed in terminal P1-15 or P5-15. Refer to Troubleshooting, "Sensor Signal (Analog, Active) - Test" if the air inlet pressure sensor is an analog sensor.
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.
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| Illustration 1 | g01065665 |
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Duty cycles that are low, medium, and high | |
The Electronic Control Module (ECM) supplies 8.0 ± 0.8 VDC to each PWM sensor.
Note: Excessive pressure can generate false "noisy signal" diagnostic codes.
If the actual air inlet pressure is greater than approximately
If the actual engine coolant pressure is greater than approximately
If a 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.
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| Illustration 2 | g01325372 |
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Schematic for the PWM sensors | |
Test Step 1. Inspect the Electrical Connectors and Wiring
- Remove the electrical power from the engine.
Note: For the following steps, refer to Troubleshooting, "Electrical Connectors - Inspect".
- Thoroughly inspect the following connectors:
- J1/P1 connectors
- J2/P2 connectors
- J7/P7 connectors
- The connectors for each PWM sensor
- Check the torque of the allen head screw for the ECM connectors.
- Perform a
45 N (10 lb) pull test on each of the wires that are associated with the circuit for the PWM sensors. - Check the harness and wiring for abrasion and for pinch points from each of the PWM sensors to the 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
- Connect Caterpillar Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".
- Switch the 35 amp circuit breaker ON. Set the engine control to the STOP mode.
- Observe the "Active Diagnostic" screen on Cat ET. Allow a minimum of thirty 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 diagnostic codes for the 8 volt supply.
Results:
- No codes - There are no active diagnostic codes for the 8 volt supply. Proceed to Test Step 3.
- Active code - There is an active diagnostic code for the 8 volt supply. This procedure will not work when this type of code is active.
Repair: Refer to Troubleshooting, "Sensor Supply - Test".
STOP
Test Step 3. Check for Active Diagnostic Codes for the PWM Sensors
- Turn on the "Active Diagnostic" screen on Cat ET. 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
- 109-3 Engine Coolant Outlet Pressure Sensor : Voltage Above Normal
- 109-8 Engine Coolant Outlet Pressure Sensor : Abnormal Frequency, Pulse Width, or Period
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, "Symptom Troubleshooting".
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, "Electrical Connectors - Inspect".
STOP
Test Step 4. Verify the Supply Voltage to the Sensor
- Set the engine control to the OFF/RESET mode.
- Disconnect the suspect sensor.
- Set the engine control to the STOP mode.
Show/hide table
Illustration 3 g00896288 Harness connector for the PWM sensors
(A) 8 volt supply
(B) Return - 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.
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.
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, "Electrical Connectors - Inspect".
STOP
Test Step 5. Verify that +Battery Voltage is Not Present in the Signal Wire
- At the harness connector for the suspect sensor, measure the voltage between terminal (B) and terminal (C).
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| Illustration 4 | g00896299 |
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Harness connector for the PWM sensors (B) Return (C) Signal | |
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 ECM.
Repair: 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 ECM.
Repair: Repair the harness, when possible. Replace the harness, if necessary.
STOP
Test Step 6. Check the Signal at the Sensor
- Set the engine control to the OFF/RESET mode.
- Remove the signal wire for the suspect sensor from terminal C of the sensor connector.
- Use a multimeter that is capable of measuring both the duty cycle and the frequency. Connect the multimeter to terminal (B) of the sensor connector and the signal wire that was removed from terminal (C) of the sensor connector.
- Set the engine control to the STOP mode.
- Measure the duty cycle and the frequency of the suspect sensor.
- Return all wiring to the original configuration.
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. 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:
- Thoroughly inspect the connector for the sensor according to Troubleshooting, "Electrical Connectors - Inspect".
- Check the duty cycle and the frequency of the sensor signal again.
- If the duty cycle and the frequency of the sensor signal are incorrect, set the engine control to the OFF/RESET mode.
- Disconnect the sensor. Connect a sensor that is known to be good. Do not install the new sensor into the engine yet.
- Set the engine control to the STOP mode. Allow a minimum of 30 seconds for any codes to activate.
- 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
- 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.
Show/hide tableTable 1 Terminals for the Connection of the Probes Suspect Sensor Connector and Terminals Engine coolant pressure (outlet) J2-68 and J1-5 Air inlet pressure J1-10 and J1-5 - Use a multimeter that is capable of measuring both the duty cycle and the frequency. Connect the multimeter to the probes.
- Measure the duty cycle and the frequency of 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 ECM is receiving a valid signal from the sensor.
Repair: Perform the following steps:
- Check "Status Screen Group 2" on Cat ET. Look for a valid signal.
26.7 kPa (3.9 psi) ). This causes the ECM to set a 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, "Configuration Parameters".Otherwise, verify that the ECM is receiving the correct voltage. Refer to Troubleshooting, "Electrical Power Supply - Test".
If the condition is not resolved, temporarily install a new ECM. Refer to Troubleshooting, "ECM - Replace".
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, "ECM - Replace".
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 the harness, if necessary.
STOP