CASE (LEFT HAND) 4S6258 - Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the speed/timing sensor. Also use this procedure if the diagnostic code in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table    
Description    Conditions which Generate this Code    System Response    
190-8 Engine Speed: Abnormal Frequency, Pulse Width or Period     The Electronic Control Module (ECM) detects an intermittent loss or complete loss of the signal from the speed/timing sensor.
The engine control switch has been in the RUN position for at least 3 seconds.     The code is logged.
The red stop lamp is illuminated.
The engine is shut down.    
678-3 ECU 8 Volts DC Supply : Voltage Above Normal     The 8 v sensor supply voltage has risen above 8.8 v for 1.5 seconds.
The engine control switch has been in the RUN position for at least 3 seconds.     The 190-8 diagnostic code is suppressed while this code is active.
The code is logged.
The amber warning lamp is illuminated.
The service tool displays "Error Indicator" on the status screen for this parameter.    
678-4 ECU 8 Volts DC Supply : Voltage Below Normal     The 8 v sensor supply voltage has dropped below 7.2 v for 1.5 seconds.
The engine control switch has been in the RUN position for at least 3 seconds.     The 190-8 diagnostic code is suppressed while this code is active.
The code is logged.
The amber warning lamp is illuminated.
The service tool displays "Error Indicator" on the status screen for this parameter.    The speed/timing sensor provides information about engine speed and the position of the camshaft to the engine ECM. A timing ring is mounted to the front of the camshaft gear. The sensor is mounted above the timing ring. As the teeth of the timing ring rotate past the pickup head, a signal is generated. The signal matches the pattern of the teeth that are on the timing ring. This signal is detected by the ECM.With the information from the speed/timing sensor, the ECM is able to calculate the position of the pistons in the cylinders. The ECM determines the desired ignition timing according to the engine speed and load. The ECM sends voltage pulses to the ignition transformers for firing the spark plugs according to the desired timing.Note: The speed/timing sensor is an active sensor that utilizes an 8 v supply voltage and integrated circuitry. Do not attempt to troubleshoot the sensor by measuring resistance across the terminals of the sensor.If a problem is detected with the signal from the speed/timing sensor during engine operation, the ECM will shut down the engine. The ECM activates the above diagnostic code.The least likely cause of this diagnostic code is a problem with the ECM.
Illustration 1 g01918293
Schematic for the engine speed/timing sensor
Illustration 2 g01918294
Location of the speed/timing sensor (right front side engine view) (1) P2 ECM connector (2) Speed/timing sensor
Illustration 3 g01918833
Terminal locations at the P2 ECM connector (10)