NUT 8C8722 - Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with one or more of the engine speed/timing sensors. Also, use this procedure if the following diagnostic code is active or easily repeated.
Table 1
Diagnostic Codes Table    
J1939 Code and Description    Conditions which Generate this 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 is set to zero rpm.
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.    The ECM provides the engine speed/timing sensor with a regulated voltage of 8.0 0.5 VDC. The engine speed/timing sensor provides a pulse signal to the ECM. The signal is created as the timing reference gear rotates past the pickup of the engine speed/timing sensor. 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 sensor generates a pulse signal to the ECM as each tooth passes the sensor. 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 signal from the engine speed/timing sensor is lost, the ECM will terminate fuel injection. A manual timing calibration is required on this engine.
Illustration 1 g03656801
Schematic for the engine speed/timing sensors
Illustration 2 g03381708
(1) Secondary engine speed/timing sensor (2) Primary engine speed/timing sensor
Illustration 3 g03381711
(3) Timing calibration sensor
Illustration 4 g03381773
P2 ECM connector (P2-26) Secondary engine speed/timing signal (P2-46) Primary engine speed/timing signal
Illustration 5 g03381777
P1 ECM connector (P1-4) +8V digital supply (P1-5) Digital return
Illustration 6 g03393169
Table 2
Troubleshooting Test Steps    Values    Results    
1. Check for Active Codes and Logged Codes
A. Connect Cat ET to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools", if necessary.
B. Restore electrical power to the ECM.
C. Start the engine and run the engine until the