ROD AS 2478904 - Caterpillar

System Operation Description:
Illustration 1 g01324839
Engine speed signal
Use this procedure to troubleshoot suspect problems with the circuit for the engine speed sensor.This procedure covers the following diagnostic codes:
342-2 Secondary Engine Speed Sensor : Erratic, Intermittent, or Incorrect
342-5 Secondary Engine Speed Sensor : Current Below Normal
342-6 Secondary Engine Speed Sensor : Not Responding Properly
342-8 Secondary Engine Speed Sensor : Abnormal Frequency, Pulse Width, or PeriodRefer to Illustration 1. The engine speed sensor is powered by the sensor supply (12 VDC) from the Auxiliary Sensing Module (ASM). A magnetic pickup is located inside the sensor. As the teeth of the flywheel rotate past the magnetic pickup, the sensor generates a signal that indicates the rpm. The ASM monitors the signal from the engine speed sensor. The ASM uses the value of engine speed in order to perform calculations that relate to engine speed and load.The ASM sends a value that indicates engine speed to the Electronic Control Module (ECM) via the Cat Data Link. The ECM calculates a value that indicates engine rpm from the signal from the engine speed/timing sensor. The ECM compares the two values.The ECM activates a "342-2 Secondary Engine Speed Sensor : Erratic, Intermittent, or Incorrect" diagnostic code and the ECM shuts down the engine when all of the following conditions are true:
A "254-9 Electronic Control Module : Abnormal Update Rate" diagnostic code is not active. This indicates that the Cat Data Link is OK.
A "320-3" or "320-8" diagnostic code is not active. This indicates that the signal from the engine speed/timing sensor is OK.
The engine speed that is derived from the engine speed/timing sensor is greater than low idle.
The value of engine speed from the ASM and the engine speed that is derived from the engine speed/timing sensor are different by more than 50 rpm.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 sensor. The least likely cause is a problem with an ECM.Logged diagnostic codes provide a historical record. Before you begin this procedure, use 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 g01330000
Schematic for the circuit of the engine speed sensor
Test Step 1. Inspect the Electrical Connectors and Wiring
Remove the electrical power from the engine. Note: For the following steps, refer to Troubleshooting, "Electrical Connectors - Inspect".
Thoroughly inspect the following connections:
J3/P3 connectors
J9/P9 connectors
Check the torque of the allen head screw for the ECM connectors.
Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit for the engine speed sensor.
Illustration 3 g01304155
Rear view
(1) Engine speed sensor
Check the harness and wiring for abrasion and for pinch points from engine speed sensor (1) to the ECM. Expected Result:The connectors, pins, and sockets are connected properly. The connectors