SWITCH-PRESSURE 4P8767 - Caterpillar

This procedure is for the parameter that has the alert indicator which is FLASHING constantly. This condition is caused by an undesired open circuit or a failed main display module.The main display module is unable to identify system errors in simple circuits. No service code is available in order to assist the operator with troubleshooting. A possible problem exists when the operation of an alert indicator does not correspond to a known condition of the machine. For example, the alert indicator always FLASHES regardless of the actual pressure of the engine oil. Before you start troubleshooting, ensure that a diagnostic code exists. For a description of normal conditions that cause these events, see the Operation and Maintenance Manual for the machine that is being serviced. Perform the following procedures only if a fault is suspected.Note: The indicator reflects the open or grounded condition of the switch inputs. When a switch input is open, the corresponding alert indicator FLASHES. When a switch input is grounded, the corresponding alert indicator is OFF. Therefore, in order to check a circuit, the service person opens the switch. Then, the service person grounds the switch. This is done while the service person is watching for the correct result on the alert indicator. Test Step 1. LOCATE THE SWITCH.
Locate the switch which corresponds to the parameter that always FLASHES the alert indicator. (If necessary, use the Electrical System Schematic in order to assist in locating the switch.) Expected Result:The appropriate switch is located.Results:
OK - The appropriate switch is located. Proceed to test step 2.Test Step 2. CHECK THE HARNESS.
Disconnect the signal wire from the switch.
Place a jumper wire from the signal wire to the ground wire. (If a ground wire is not present, connect the signal wire to frame ground.) Expected Result:The alert indicator continues FLASHING.Results:
YES - The alert indicator continues FLASHING. The machine harness is open or the main display module has failed. Proceed to test step 3.
NO - The alert indicator stops FLASHING. The circuit is operating correctly. The switch has failed.Repair: Check or replace the switch.STOPTest Step 3. CHECK THE HARNESS.
Turn the disconnect switch and the key start switch to the OFF position.
On the Electrical System Schematic, trace the signal wire from the switch to the main display module.
Determine the signal contact (connector contact) of the machine harness at the main display module.
Disconnect the machine harness from the main display module.
At the machine harness connector for the main display, check for continuity between the signal contact and contact 2 or frame ground if a ground wire is not present at contact 2. (The jumper is in place from the previous test.) Expected Result:The resistance is greater than 5.0 ohms.Results:
YES - The resistance is greater than 5 ohms.Repair: Repair the harness or replace the harness.STOP
NO - The resistance is less than 5 ohms. The harness is not causing the problem. The main display module has failed.Repair: It is unlikely that the main display module has failed. Exit this procedure and perform this