GUARD 3186247 - Caterpillar

show a 5 2 kPa (0.7 0.3 psi) drop in pressure while the vacuum is being applied. An analog sensor is not producing the correct reading. Proceed to test step 12.
Not OK Digital - The ET does not show the correct temperature. A digital sensor is not producing the correct reading. Proceed to test step 13.
Vacuum Leak - A vacuum leak is suspected.Repair: Check for leaks. If no leaks are found, there is an internal leak in the suspect pressure sensor. Replace the sensor and calibrate the sensor. Reset the system and note any active diagnostic codes.STOPTest Step 12. Check the Analog Sensor's Signal Voltage at the Sensor Connector.
Turn the Battery switch for the ECM to the OFF position.
Install a Breakout T at the sensor connector.
Turn the Battery switch for the ECM to the ON position.
Measure the sensor signal voltage between pin C and pin B at the sensor connector.
Remove the Breakout T and reconnect the sensor.Expected Result:The signal voltage should be between 0.2 VDC and 4.8 VDC for analog sensors.Results:
OK - The signal voltage is between 0.2 VDC and 4.8 VDC for analog sensors. Proceed to test step 16.
Not OK - The signal voltage is not between 0.2 VDC and 4.8 VDC for analog sensors. Proceed to test step 14.Test Step 13. Check the Digital Sensor's Signal Frequency and the Duty Cycle at the Sensor Connector.
Turn the Battery switch for the ECM to the OFF position.
Install a Breakout T at the sensor connector.
Turn the Battery switch for the ECM to the ON position.
Measure the frequency and the duty cycle between pin C and pin B of the suspect digital sensor at the sensor connector.
Turn the Battery switch for the ECM to the OFF position.
Remove the Breakout T and reconnect the sensor.Expected Result:The frequency reading should be between 400 Hz and 800 Hz.When the temperature is below 49 °C (120 °F), the duty cycle should be between 16% to 21%.When the temperature is between 49 °C (120 °F), and 851 °C (1564 °F) the duty cycle should be between 22% to 88%.Results:
OK - The frequency and the duty cycle are correct. Proceed to test step 17.
Not OK - The frequency and the duty cycle are not correct. Proceed to test step 14.Test Step 14. Check for Shorts in the Wiring Harness.
Turn the Battery switch for the ECM to the OFF position.
Disconnect the ECM connectors J1/P1 and J2/P2. Disconnect the suspect sensor.
Measure the resistance between the suspect sensor signal wire at the ECM connector and the supply voltage at the ECM connector.
Measure the resistance between the suspect sensor signal wire at the ECM connector and the sensor return line at the ECM connector.
Measure the resistance between the suspect sensor signal wire at the ECM connector and engine ground.Expected Result:The resistance should be greater than 20,000 Ohms.Results:
OK - The resistance is greater than 20,000 Ohms. Proceed to test step 15.
Not OK - The resistance is less than 20,000 Ohms.Repair: Repair the connectors or wiring and/or replace the