SWITCH AS-ROTARY 7T9303 - Caterpillar

System Operation Description:Use this procedure to troubleshoot the electrical system if a problem is suspected with the primary engine speed/timing sensor or with the secondary engine speed/timing sensor. Use this procedure to troubleshoot the electrical system if a diagnostic code in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table    
Code and Description     Conditions which Generate this Code     System Response    
190-2 Engine Speed Sensor erratic, intermittent, or incorrect     The signal from the primary engine speed/timing sensor has been lost.
The code is logged only if the engine has been running for three seconds.     The code is logged.
If a valid signal is not received from the primary engine speed/timing sensor, the Electronic Control Module (ECM) will default to the secondary engine speed/timing sensor. The engine will shut down only if the signals from the primary engine speed/timing sensor and the secondary engine speed/timing sensor are abnormal.
The injector solenoids may fire erratically.    
190-3 Engine Speed Sensor voltage above normal     The supply voltage for the primary engine speed/timing sensor is above normal.    
190-8 Engine Speed Sensor abnormal frequency, pulse width, or period     The signal from the primary engine speed/timing sensor has been incorrect for at least five seconds.    
342-2 Secondary Engine Speed Sensor erratic, intermittent, or incorrect     The signal from the secondary engine speed/timing sensor has been lost.
The code is logged only if the engine has been running for three seconds.     The code is logged.
The engine will shut down only if the signals from the primary engine speed/timing sensor and the secondary engine speed/timing sensor are abnormal.
The injector solenoids may fire erratically.    
342-3 Secondary Engine Speed Sensor voltage above normal     The supply voltage for the secondary engine speed/timing sensor is above normal.    
342-8 Secondary Engine Speed Sensor abnormal frequency, pulse width, or period     The signal from the secondary engine speed/timing sensor has been incorrect for at least five seconds.    The engine uses two engine speed/timing sensors. Both sensors detect the reference for engine speed and timing from a timing reference ring with a unique pattern that is on the rear face of the fuel injection pump gear. The ECM uses the pattern of the pulses in order to determine the position of the crankshaft. The ECM measures the time between the pulses that are created by the sensors as the gears rotate in order to determine rpm.Under normal operation, the primary speed/timing sensor determines when the piston in the number 1cylinder is at the top of the compression stroke. When the timing has been established, the sensor signal is used to determine engine speed.When the timing has been established, the ECM triggers each injector in the correct firing order at the correct time. The actual timing and duration of each injection is based on engine rpm and on load. The secondary speed/timing sensor provides continuous operation of the engine if the primary engine speed/timing sensor fails. If the engine is running and the