PIN 0002669 - Caterpillar

Illustration 1 g01005269
Schematic of the pressure switch (low park brake)Test Step 1. CHECK THE NORMALLY CLOSED CIRCUIT FOR PROPER OPERATION.
Turn the key start switch to the ON position. Do NOT start the engine.
Disconnect the pressure switch from the machine harness.
At the machine harness connectors, measure the voltage from contact 1 (wire C491-PU) to contact 2 (wire J764-BR). Expected Result:Voltage should be between 4.0 VDC and 5.25 VDC.Results:
OK - The voltage is with an acceptable range. Proceed to test step 2.
NOT OK - The voltage is not with an acceptable range. Repair: The machine harness has failed. The return circuit (wire J764-BR) is open or the normally closed circuit (wire C491-PU) is open or shorted. Repair the machine harness or replace the machine harness.STOPTest Step 2. CHECK THE SWITCH FOR NORMAL OPERATION.
Remove the pressure switch and replace the switch with a gauge that is capable of at least 3000 kPa (435 psi).
Start the engine and run the engine at high idle.
Engage the parking brake. Measure the pressure.Expected Result:When the parking brake is engaged, the pressure should be greater than 400 kPa (58 psi).Results:
OK - The pressure is correct.Repair: The switch has failed. Replace the pressure switch for the hydraulic system pilot. Verify that the new switch corrects the problem.STOP
NOT OK - The pressure is not correct.Repair: There is a problem with the hydraulic system. Refer to Testing and Adjusting, "Initial Pressure Tests".STOPTest Step 3. CHECK IF THE PROBLEM REMAINS.
Clean the contacts of the harness connectors.
Reconnect all harness connections.Expected Result:The switch operates correctly.Results:
OK - The switch operates correctly. The problem does not exist at this time. The initial problem was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.STOP
NOT OK - The switch does not operate correctly.Repair: Replace the switch.STOP