0394892 JOHNSON CHECK VALVE ASSY.

Table 1
Diagnostic Codes Table
CDL 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. 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 the next engine start-up. If a failure mode for the primary engine speed/timing sensor is detected during engine start-up, timing calibration is aborted. The value of the timing offset stored in ECM memory will be used. This value will continue to be used for the engine timing calibration until the diagnostic is resolved. A timing calibration cannot be performed manually on this engine.
Illustration 1 g02968596
Schematic for the engine speed/timing sensors
Illustration 2 g02724104
P2 ECM connector
(P2-29) +8V supply (primary ECM)
(P2-35) Primary engine speed/timing signal (primary and secondary ECM)
(P2-46) Secondary engine speed/timing signal (primary and secondary ECM)
Illustration 3 g02724105
P1 ECM connector
(P1-5) Secondary digital return (primary ECM only)
(P1-18) Primary digital return (primary ECM only)
Table 2
Troubleshooting Test Steps Values Results
1. Check for Diagnostic 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 engine is at normal operating temperature.
Note: If the engine will not start, monitor the engine rpm on Cat ET while the engine is being cranked. If necessary, power Cat ET from another battery while the engine is being cranked.
E. Look for these codes on Cat ET:
- 190-08
- 723-08
Codes
Results: None of the diagnostic codes that are listed above are active or logged.
Repair: If the diagnostic codes that are listed above are not active or logged, and the engine is not running properly, refer to the appropriate engine symptom in this Troubleshooting manual.
Results: A 190-08 or a 723-08 code is active or logged.
Proceed to Test Step 2.
Results: No engine rpm. - Cat ET is not reporting engine rpm for at least one engine speed/timing sensor while the engine is cranked.
Proceed to Test Step 3.
2. Check the Installation of the Sensor Assembly
A. Turn the main disconnect switch to the OFF position.
B. Visually inspect the sensors without removing the sensor assembly