The Electronic Control Module (ECM) supplies 8.0 ± 0.8 VDC to the following sensors:
- Engine coolant pressure (outlet)
- Inlet manifold air pressure
- Atmospheric pressure (if equipped)
The ECM supplies 5.0 ± 0.5 VDC to the humidity sensor (if equipped).
Note: Excessive pressure can generate false "noisy signal" diagnostic codes.
If the actual inlet manifold air pressure is greater than approximately
If the actual engine coolant pressure is greater than approximately
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 an 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 1 | g01075596 |
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Schematic of the circuit for the PWM sensors | |
Test Step 1. Inspect the Electrical Connectors and Wiring
- Set the engine control to the OFF/RESET mode. Switch 16 amp circuit breaker (3) to the OFF position.
Note: For the following steps, refer to Troubleshooting, "Inspecting Electrical Connectors".
- Thoroughly inspect the following connectors:
- J1/P1 connectors
- J2/P2 connectors
- J12/P12 connectors on the terminal box
- Check the torque of the allen head screw for the ECM connector. The proper torque is
6 ± 1 N·m (55 ± 9 lb in) .Show/hide table
Illustration 3 g01075551 Harness sides of the P1 connector
(P1-2) 5 volt supply
(P1-3) Return
(P1-4) 8 volt supply
(P1-5) Return
(P1-10) Signal for the inlet manifold air pressure
(P1-11) Signal for the humidity
(P1-12) Signal for the atmospheric pressureShow/hide table
Illustration 4 g01075555 Harness sides of the P2 connector
(P2-68) Signal for the engine coolant pressure (outlet)Show/hide table
Illustration 5 g00896248 Harness side of the P12 connector
(P12-A) 5 volt supply
(P12-C) Return
(P12-D) Signal for the atmospheric pressure
(P12-G) Signal for the humidity
(P12-L) 8 volt supply
(P12-M) Signal for the inlet manifold air pressure
(P12-N) Return
(P12-P) Signal for the engine coolant pressure (outlet) - Perform a
45 N (10 lb) pull test on each of the wires that are associated with the circuit for the PWM sensors.Show/hide table
Illustration 6 g01075559 Left side view
(1) Sensor for the engine coolant pressure (outlet)
(2) Sensor for the inlet manifold air pressureShow/hide table
Illustration 7 g01075564 Left side views
(3) Sensor for humidity
(4) Sensor for atmospheric pressure - Check the harness and wiring for abrasion and for pinch points from each PWM sensor to the ECM.
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| Illustration 2 | g01075546 |
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(1) ECM connectors J2/P2
(2) ECM connectors J1/P1 (3) 16 amp circuit breaker (4) J12/P12 connectors for the harness from the PWM sensors | |
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 "8 Volt DC Supply" Diagnostic Codes and "5 Volt Sensor DC Supply" Diagnostic Codes
- Connect the Caterpillar Electronic Technician (ET) to the service tool connector on the terminal box. Refer to Troubleshooting, "Electronic Service Tools".
- Switch the 16 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:
- 41-03 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
- Turn on the "Active Diagnostic" screen on Cat ET. Determine if any of these diagnostic codes are active:
- 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:
None of the above codes are active.
Results:
- OK - 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
- 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
- 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 8 g00896288 Harness connector for the PWM sensors
(A) 8 volt supply or 5 volt supply
(B) Return - 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 +8.0 ± 0.4 VDC. If you are troubleshooting the humidity sensor, the voltage is +5.0 ± 0.5 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 on the Signal Wire
- At the harness connector for the suspect sensor, measure the voltage between terminals B and C.
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| Illustration 9 | g00896299 |
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Harness connector for the PWM sensors (B) Return (C) Signal | |
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 approximately 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 mode. Switch the 16 amp circuit breaker OFF. 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: Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF. Repair the harness, when possible. Replace parts, if necessary.
STOP
Test Step 6. Check the Signal at the Sensor
- Set the engine control to the OFF/RESET mode.
- Install a 8T-8726 Adapter Cable As (Three-Pin Breakout) at the harness connector for the suspect sensor.
- Use a multimeter that is 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.
- Set the engine control to the STOP mode.
- 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, the inlet manifold pressure sensor, or the atmospheric pressure sensor. The duty cycle is between 10 and 90 percent for the signal from 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 signal from the engine coolant pressure sensor, the inlet manifold pressure sensor, or the atmospheric pressure sensor. The duty cycle is between 10 and 90 percent for the signal from the humidity sensor. 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:
- Thoroughly inspect the connector for the sensor according to Troubleshooting, "Inspecting Electrical Connectors".
- Check the duty cycle and the frequency of the sensor's signal again.
- If the duty cycle or the frequency of the sensor's signal is 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
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- 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 table
Table 1 Terminals for the Connection of the Probes Suspect Sensor Connector and Terminals 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 - Use a multimeter that is capable of measuring both the duty cycle and the frequency of a signal. Connect the multimeter to the probes.
- Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.
- 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 signal from the engine coolant pressure sensor, the inlet manifold pressure sensor, or the atmospheric pressure sensor. The duty cycle is between 10 and 90 percent for the signal from 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 signal from the engine coolant pressure sensor, the inlet manifold pressure sensor, or the atmospheric pressure sensor. The duty cycle is between 10 and 90 percent for the signal from 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:
- Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.
- Check "Status Screen Group 2" on Cat ET. Look for a value from the suspect sensor that is valid.
26.7 kPa (3.87 psi) ). This causes the 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 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