DISC (8 TEETH) 2H6936 - Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with one or more of the engine speed/timing sensors. Or, use this procedure if one of the following diagnostic codes is active.
Table 1
Diagnostic Codes Table
J1939 Code and Description Conditions which Generate the Code System Response
190-8
Engine Speed Sensor : Abnormal Frequency, Pulse Width, or Period The Electronic Control Module (ECM) detects an abnormal signal frequency. The engine speed from this sensor is ignored.
The code is active.
The code is logged if the pattern from the timing ring returns for five seconds.
723-8
Engine Speed Sensor #2 : Abnormal Frequency, Pulse Width, or Period The ECM detects an abnormal signal frequency. The code is latched in the active state until the power to the ECM is cycled.
The offset for the timing calibration is set to zero while the diagnostic code is active.
The sensor is ignored. The engine speed is calculated by using only the signal from the primary speed/timing sensor.
723-19
Engine Speed Sensor #2 : Data Error The Integrated Sensing Module (ISM) has lost the camshaft differential speed signal. The ECM has been notified by the ISM that the engine speed signal is no longer detected.
The engine is shutdown.
The code is logged. The ECM provides the engine speed/timing sensors with a regulated voltage of 8.0 0.5 VDC. The engine speed/timing sensors provide a pulse signal to the ECM. The signal is created as the timing reference gear rotates past the pickup of the engine speed/timing sensors. The timing reference gear is mounted on the rear of the left camshaft. A unique tooth pattern on the timing reference gear allows the ECM to determine the crankshaft position, rotation, and rpm.The engine speed/timing sensors generate a pulse signal to the ECM as each tooth passes the sensors. The ECM counts the pulses in order to determine the engine rpm. The ECM memorizes the pattern of the pulses. The ECM compares that pattern to a standard pattern in order to determine the crankshaft position. The ECM uses this information to determine the position of the No. 1 cylinder. The ECM then triggers each unit injector to fire in the correct firing order and at the correct time. The actual timing and duration of each injection is determined by the ECM. The ECM uses engine rpm and engine load to determine the timing and duration of injection. The loss of a signal from an engine speed/timing sensor generates a diagnostic on Caterpillar Electronic Technician (ET). If the signals from both the primary engine speed/timing sensor and the secondary engine speed/timing sensor are lost, the ECM will terminate fuel injection.Under normal operation, the ECM utilizes the signal from the primary speed/timing sensor to determine the crankshaft position for an accurate fuel delivery and timing. This feature eliminates the need for a separate procedure for timing calibration. A timing offset is determined during each engine start-up. The value of the timing offset is stored in the non-volatile memory of the ECM until the successful completion of