PIN 7T4810 - Caterpillar

System Operation Description:Use this procedure to troubleshoot the electrical system if a problem is suspected with the circuit for the engine speed/timing sensor or if one of the diagnostic codes in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table    
Code    Conditions which Generate this Code    System Response    
190-2 Engine Speed Sensor : Erratic, Intermittent, or Incorrect     The crankshaft is rotating faster than the cranking speed and the signal from the engine speed/timing sensor is lost for at least one second.     The shutdown output is activated. The code is logged.
If the engine is not running, the engine will not start. If the engine is running, the engine is shut down.    
190-8 Engine Speed Sensor : Abnormal Frequency, Pulse Width, or Period     The crankshaft is rotating faster than the cranking speed. The signal from the engine speed/timing sensor is lost but the signal returns within one second.    The engine speed/timing sensor provides information about engine speed and about the position of the crankshaft to the Electronic Control Module (ECM). The sensor monitors the rotation of a speed-timing wheel. The passive sensor has a coil around a permanent magnet which generates voltage as the teeth of the speed-timing wheel pass through the magnetic field. The speed-timing wheel is installed on the rear of the right camshaft.The engine speed/timing sensor generates a signal that matches the pattern of the speed-timing wheel's teeth. The ECM monitors the speed of the signal pulses in order to determine the engine rpm.The speed-timing wheel has a special tooth pattern that indicates the position of the camshaft. The speed-timing wheel has 36 teeth that are evenly spaced and one extra tooth. The number one cylinder is at the top center position on the compression stroke when the centerline of the first tooth after the extra tooth aligns with the centerline of the sensor. All 37 teeth pass the sensor during one revolution of the camshaft or two revolutions of the crankshaft.With the information from the engine speed/timing sensor, the ECM is able to calculate the positions of the pistons in the cylinders. The ECM determines the desired ignition timing according to the engine speed and to the load. If detonation is detected in any of the cylinders, the ECM retards the timing of the affected cylinders. The ECM sends voltage pulses to the ignition transformers for firing the spark plugs according to the desired timing.If the ECM detects a problem with the engine speed/timing sensor's signal, the ECM will shut down the engine. If there is a problem with the engine speed/timing sensor's signal during start-up, the ECM will not initiate the ignition. The engine will not start. The corresponding diagnostic code is generated.If the engine speed/timing sensor is replaced, the sensor does not require calibration and the speed-timing wheel does not require adjustment.The most likely causes of the diagnostic code are a poor electrical connection or a problem in a wiring harness. The next likely