Troubleshooting The Manual Modulation Pressure Switch Caterpillar

Troubleshooting The Manual Modulation Pressure Switch

Usage:

MOTOR GRADERS120H (2AN, 3GR, 4MK, 5FM, 6NM, 6TM, 9FN, 9YR),
135H (3YK, 7MM, 8WN),
12H (2GS, 2LR, 2WR, 4ER, 4XM, 5ZM, 8MN),
140H (2ZK, 3AS, 3FR, 5HM, 8JM, 8KM, 9TN, 9ZN),
143H (1AL),
160H (2HS, 2FM, 3GM, 3HR, 6WM, 9EJ, 9JM),
163H (5AK) MOTOR GRADERS

Problem:

Problems have been reported of difficulty in troubleshooting manual modulation problems on the above motor graders. The 111-7088 Pressure Switch is an important component to consider, but there is a lack of troubleshooting information on this switch. Also, the set points sometimes vary from the specification.

Solution:

The following brief explanation provides a procedure to troubleshoot the 111-7088 Pressure Switch, which is used to communicate to the ECM when the manual modulation pedal is being used. When the pedal is depressed, the pressure switch opens and the ECM logic determines the correct OFF/ON directional clutch solenoid positions. During a speed change, the ECM determines transmission oil temperature and will switch the directional clutch solenoid to the OFF position when the oil is cold (less than 0 deg C or 32 deg F). The solenoid is left ON with warmer oil. During a directional shift, the ECM will turn the directional clutch solenoid to OFF and leave the range and speed clutch solenoids ON. Once the operator starts raising the modulation pedal, the pressure switch will close at 75 Kpa (11 psi). Once closed, the ECM completes the shift sequence by switching the proper clutch solenoids ON or OFF. If the pressure switch fails, the ECM shift sequence may not begin at the proper time and clutch modulation will be affected.

The easiest method to troubleshoot the pressure switch is to disconnect the machine wiring harness from the switch. Jumper the two wires in the harness together using a 4E-2898 Plug Assembly or like jumper wire. Operate the machine to determine if the modulation problem remains. If there isn't a modulation problem, the 111-7088 Pressure Switch has failed and should be replaced. If the modulation problem remains, the problem is not in the pressure switch. Remove the jumper wire and connect the harness back to the pressure switch. The problem will be either cable adjustment or the modulation spool in the transmission hydraulic control valve.