FILTER 3717271 - Caterpillar

System Operation Description:
Illustration 1 g01089416
Speed/timing sensor and timing ringThe speed/timing sensor provides information about engine speed and the position of the crankshaft to the master Electronic Control Module (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 plastic sliphead 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.The timing ring has a special tooth pattern that indicates the position of the camshaft and the direction of rotation. The timing ring has 24 slots in the outer diameter. Twenty-one of the slots are narrow. Three of the slots are about 2.5 times wider than the rest of the slots. When the engine rotates in the normal direction, the slots pass the speed/timing sensor in the following order:
1 wide slot
3 narrow slots
2 wide slots
18 narrow slotsThe number one cylinder is at the top center position when the leading edge of the third narrow slot passes the center of the sliphead. All 24 teeth pass the sliphead during one revolution of the camshaft or two revolutions of the crankshaft.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. The corresponding diagnostic code is not activated.The most likely causes of the diagnostic code are 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.Logged diagnostic codes provide a historical record. Before you begin this procedure, use the Caterpillar Electronic Technician (ET) to print the logged codes to a file.The troubleshooting procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.
Illustration 2 g01091094
Schematic for the circuit of the speed/timing sensorTest Step 1. Inspect the Electrical Connectors and Wiring
Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine.Note: For the following steps, refer to Troubleshooting, "Inspecting Electrical Connectors".
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