CAP 8S4951 - Caterpillar

System Operation Description:The engine contains the following Pulse Width Modulated sensors (PWM):
Engine coolant pressure (outlet)
Air inlet pressureThis 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 PeriodNote: 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.
Illustration 1 g01065665
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 338 kPa (49 psi), a 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 109-8 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 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 g01325372
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