COVER-FUEL RATIO 8N3799 - Caterpillar

System Operation Description:Use this procedure to troubleshoot the electrical system if a problem is suspected with the sensors or if any one of the diagnostic codes in Table 1 is active or easily repeated.
Table 1
Diagnostic Codes Table    
Code and Description    Conditions which Generate this Code    System Response    
94-3 Fuel Delivery Pressure Sensor voltage above normal     The Electronic Control Module (ECM) detects signal voltage that is above normal for eight seconds.     The code is logged.
The value of the parameter is set to a gauge pressure of
600 kPa (87 psi).    
94-4 Fuel Delivery Pressure Sensor voltage below normal     The ECM detects signal voltage that is below normal for eight seconds.    
100-3 Engine Oil Pressure Sensor voltage above normal     The ECM detects signal voltage that is above normal for eight seconds.     The code is logged.
The value of the parameter is set to a gauge pressure of
600 kPa (87 psi).    
100-4 Engine Oil Pressure Sensor voltage below normal     The ECM detects signal voltage that is below normal for eight second.    
1785-3 Intake Manifold Pressure Sensor voltage above normal     The ECM detects signal voltage that is above normal for two seconds.     The code is logged.
The value of the parameter is set to a gauge pressure of
100 kPa (15 psi).    
1785-4 Intake Manifold Pressure Sensor voltage below normal     The ECM detects signal voltage that is below normal for two seconds.    System OperationUse this procedure to troubleshoot any suspect problems with the following sensors:
Fuel pressure sensor
Engine oil pressure sensor
Intake manifold pressure sensorThe supply voltage is routed to terminal A of each sensor connector. The sensor return is routed to terminal B of each sensor connector. The sensor signal is routed to terminal C of each sensor connector. The ECM provides short circuit protection for the internal power supply. A short circuit to the battery will not damage the internal power supply.The ECM performs an automatic calibration of these sensors whenever the ECM is powered and the engine is off for at least five seconds. During an automatic calibration, the ECM calibrates pressure sensors to the value of the atmospheric pressure at sea level. This calibration value is then checked against an acceptable offset pressure range.The ECM continuously outputs a pull-up voltage on the input terminal from an analog sensor. The ECM uses this pull-up voltage in order to detect an open or a short in the signal circuit. When the ECM detects the presence of a voltage that is above the normal range of the sensor on the signal circuit, the ECM will generate an open circuit diagnostic code -3 for that sensor. When the ECM detects the absence of the pull-up voltage on the signal circuit, the ECM will generate a short circuit diagnostic code -4 for that sensor. The presence of pull-up voltage at the sensor connector indicates that the wires from the sensor connector to the ECM are not open or shorted to