CENTRAL AND LOWER STRUCTURE 5P8953 - Caterpillar

System Operation Description:Use this procedure to troubleshoot a suspected problem with the circuit that is for the engine speed/timing sensor or use this procedure if one of the diagnostic codes in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table    
Description    Conditions which Generate this Code    System Response    
145-3 12 Volt DC Power Supply : Voltage Above Normal     The 12 volt power supply is above normal for two seconds.     The code is logged.
The alarm output is activated.
The shutdown output is activated.
The engine is shut down.    
145-4 12 Volt DC Power Supply : Voltage Below Normal     The 12 volt power supply is below normal for two seconds.    
320-3 Speed/Timing Sensor short to +batt     While the engine speed is greater than 280 rpm, the Electronic Control Module (ECM) has lost the signal for the timing gear pattern for 1.3 seconds.    
320-8 Engine Speed/Timing signal abnormal     While the engine speed is greater than 280 rpm, the ECM has detected an invalid signal for the timing gear pattern and a valid timing signal returns within one second.    The speed/timing sensor provides information about engine speed and the position of the crankshaft to the master ECM and to the slave ECM. The sensor is powered by the sensor supply (12 VDC) from the master ECM. A magnetic pickup is located in the pickup head of the sensor. The timing ring is mounted on the rear of the left camshaft. As the teeth of the ring rotate past the sliphead of the sensor, the sensor generates a signal that matches the pattern of the teeth.With the information from the engine speed/timing sensor, each ECM is able to calculate the positions of the pistons in the cylinders. Each ECM determines the desired ignition timing according to the engine speed and load. If detonation is detected in any of the cylinders, the appropriate ECM retards the timing of the affected cylinders. Each ECM sends voltage pulses to the ignition transformers for firing the spark plugs according to the desired timing.During engine operation, the master ECM will shut down the engine if either ECM detects a problem with the signal from the speed/timing sensor. The ECM that detected the problem with the signal will activate the corresponding diagnostic code.If there is a problem with the engine speed/timing sensor's signal during start-up but no corresponding diagnostic code is active, the master ECM will not initiate the ignition. The engine will not start. Unless the engine speed exceeds 280 rpm, the corresponding diagnostic code will not be activated.The most likely causes of diagnostic codes is a poor electrical connection or a problem in a wiring harness. The next likely cause is a problem with the engine speed/timing sensor. The least likely cause is a problem with an ECM.
Illustration 1 g01413730
Schematic of the circuit for the engine speed/timing sensorTest Step 1. Inspect the Electrical Connectors and the Wiring
Set the engine control switch to the OFF/RESET position. Remove