WIRE A 7H2608 - Caterpillar

Pump Pressure Sensors Secondary Steer Attachment
When the secondary steering attachment is installed, two pressure sensors are used to monitor "resolved" pump pressure. The sensors will monitor the main steering pump pressure or the secondary steering pump pressure, whichever is highest. The two sensors provide redundancy. Both sensors provide an input signal to the primary steering ECM, however, each sensor provides a different type of input signal to the ECM.The Steering Pump Oil Pressure Sensor 2 provides a PWM input signal to the primary steering ECM. The primary steering ECM 8 VDC power supply is used to power this pump pressure sensor. The ECM will give the PWM signal from sensor 2 priority when determining the pump pressure. If problem is detected in this sensor circuit, the ECM will use the signal from the Steering Pump Oil Pressure Sensor 1 signal as the backup.The Steering Pump Oil Pressure Sensor 1 provides analog voltage input signal to the Primary Steering ECM. The Primary Steering ECM 5 VDC power supply is used to power the sensor 1. This sensor provides a 0.5 VDC to 4.5 VDC voltage signal to the ECM that will correspond to the monitored pump pressure.The approximate signal voltages for the listed pump pressures are in the following table.
Table 1
Steering Pump Oil Pressure Sensor 1 Signal Voltage versus Pressure    
Pressure     Signal Voltage     Pressure     Signal Voltage    
6895 kpa (1000 psi)     0.9 VDC     24.1 mpa (3500 psi)     2.9 VDC    
13.8 mpa (2000 psi)     1.7 VDC     25.6 mpa (4000 psi)     3.3 VDC    
17.2 mpa (2500 psi)     2.1 VDC     31.0 mpa (4500 psi)     3.7 VDC    
20.7 mpa (3000 psi)     2.5 VDC     34.5 mpa (5000 psi)     4.0 VDC    The Steering Pump Oil Pressure Sensor 2 provides a PWM output signal in the range of 5 percent to 95 percent to the Primary Steering ECM. The duty cycle of the PWM signal corresponds to the monitored pump pressure.Secondary Steering System Activation and Control
When the Primary Steering ECM detects certain failure mode conditions in the primary steering system, the ECM will notify the Transmission ECM to activate the secondary steering system. The abnormal condition that is detected will determine which of the following operational modes will be activated:
The redundant steering solenoid valves can be activated only.The diagnostics that the Primary Steering ECM will use to request activation of the redundant steering solenoid valves are listed in prior text under the "Secondary Steering Redundant Solenoid Valve System"title.The Primary Steering ECM will use Pulse Width Modulated (PWM) signals on the secondary steering request circuit (U738-PU) to notify the Transmission ECM to activate and control the secondary operation. The duty cycle on this circuit will indicate the mode or operation that the Transmission ECM will activate.The PWM duty cycles and the requested corresponding secondary steer modes of operation are:
20 percent - indicates normal operation of the primary steering system.
40 percent - request to activate secondary steering pump