LUG 3745282 - Caterpillar

Illustration 1 g03531897
Schematic for the Brake Air Pressure SensorThe schematic that is shown above represents a typical installation of the component. Verify the connector contact and the wire numbers by using the Electrical System Schematic for the machine that is being serviced. This diagnostic code indicates the Monitor ECM has detected that the brake air pressure sensor signal is abnormal. The signal may have one of the following abnormal characteristics:
Frequency
Pulse width
Period - Important - On certain Small Off Highway Trucks the brake air pressure sensor must be matched to the flash file used in the Monitor ECM. If a 265-6874 Software Group or later flash file is used, the 185-0600 Pressure Sensor Gp must be installed. Refer to Service Magazine, SEPD0896, "New Software is Available for the CAT Monitoring System".The Pulse Width Modulation (PWM) pressure sensor has an operating duty cycle from 0% to 100%. The pressure and duty cycle relationship is linear.
Table 1
Specifications for Brake Air Pressure Sensors    
    153-3962 Pressure Sensor Gp     185-0600 Pressure Sensor Gp    
Sensor Pressure Range (Absolute)     0 to 3163 kPa (459 psi)     0 to
1135 kPa (165 psi)    
Output Duty Cycle at Atmospheric Press     7.5% 3%     9.8% 3%    
Frequency Range of Output Signal     5 1 kHz     5 1 kHz    The following can cause this code:
Sensor signal circuit shorted to ground
Sensor failure
ECM failureNote: This test procedure may create other diagnostic codes. Ignore and clear these created codes after the original diagnostic code has been corrected. Ensure diagnostic code 601-8 is active before performing this procedure.Note: Use a calibrated digital multimeter for this procedure.Test Step 1. CHECK THE SENSORReference Troubleshooting, "Pulse Width Modulated Sensor"
Turn on the disconnect switch and the keyswitch.
Disconnect the sensor from the harness while observing the diagnostic code status.Expected Result:601-8 remains active and the FMI does not change. Results:
OK - 601-8 remains active and the FMI does not change. The sensor is likely correct. Proceed to Test Step 2.
NOT OK - 601-8 is not active and the FMI changes. The sensor has failed.Repair: Replace the sensor.STOPTest Step 2. CHECK FOR A SHORT TO GROUND
Turn off the keyswitch and the disconnect switch.
Disconnect the harness from the sensor.
Disconnect the harness from the ECM.
At the harness connector for the ECM, measure the resistance from contact 37 (wire 408-WH) to all contacts of the harness connectors for the ECM.Expected Result:Each resistance is greater than 5000 ohms.Results:
OK - Each resistance is greater than 5000 ohms. Proceed to Test Step 3.
NOT OK - A resistance is less than 5000 ohms. There is a short between contact 37 (wire 408-WH) and the circuit with low resistance. Repair: Repair or replace the harness.STOPTest Step 3. CHECK THE DIAGNOSTIC CODEThe keyswitch and the disconnect switch remain off.
Inspect the harness.Reference Testing and Adjusting , "Electrical Connector - Inspect"
Testing and Adjusting , "Wiring Harness (Short Circuit) - Test"
Clean the harness connector contacts
Inspect the harness connector contacts for corrosion or damage
Inspect the wire insulation for damage caused