CAB GP 3574078 - Caterpillar

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(2) Engine speed sensor.The engine speed sensor is located on top of the flywheel housing on the rear engine module.
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Schematic Of The Engine Speed SensorThis diagnostic code is recorded when the brake/cooling ECM receives an incorrect engine speed sensor signal from the speed sensor. The signal is below the dropout signal level. The engine must be running. The incorrect signal that is being read by the brake/cooling ECM has the following characteristics: erratic, intermittent and incorrect. The brake/cooling ECM determines that this condition exists by comparing signal information. The brake/cooling ECM compares the engine speed sensor signal on the data link to the signal that is being read on contact J1-40 of the brake/cooling ECM. This failure will cause the ECM to lose the function of automatic retarding.One of the following conditions must be present before the diagnostic code will be active:
The signal from the engine speed sensor to the brake/cooling ECM is incorrect.
The brake/cooling ECM is NOT receiving the correct information about the engine speed sensor over the data link.Note: Check for other related diagnostic codes before performing the following diagnostic code procedure. Check for an active CID 0248 FMI 12. Correct the related CID 0248 FMI 12 first. Then view the status of the other diagnostic codes and correct the other active codes.
When it is necessary to work under the machine with the body (bed) raised, attach the body (bed) retaining cables to the rear tow points. Install the rear tow point pins through the ends of the retaining cables.Failure to properly secure the body (bed) may result in personal injury or death.
Test Step 1. CHECK THE SENSOR RESISTANCE.
Turn the key start switch and the disconnect switch to the OFF position.
Disconnect the machine harness from the speed sensor.
At the connector for the speed sensor, measure the resistance between the two