MANIFOLD 3G3712 - Caterpillar

Machines With Electronic Controls Or Electronic Monitors Which Use Built In DiagnosticsReference: Electrical System Schematic for the particular machine. Service Manual module for the particular electronic control system. Description
Service codes contain three levels of information which describe one problem. The levels of the service code are MID, CID, FMI. These codes most often describe an electrical fault or failure in the ELECTRICAL system. These codes are not to be confused with an abnormal condition in the ENGINE or machine SYSTEM such as high engine coolant temperature.
The service codes that apply to a given machine are listed on the back of the electrical system schematic which is in the service manual for the machine being serviced.
MID - The MID (Module Identifier) tells which electronic control system has detected the problem. The MID is shown in the format of MIDnnnn. Where nnnn is a number describing the electronic control system. Such as: electronic engine control (36), electronic transmission control (81) or computerized monitoring system (26). The MID number can be any length from n to nnnn.
CID - The CID (Component Identifier) tells which component (or circuit) in the MID system has the problem. This code can point to items like an engine speed sensor (190), transmission oil temperature sensor (177) or 8 Volt sensor power supply (263).
FMI - The FMI (Failure Mode Identifier) tells what is believed to be wrong with the component that the CID is describing. Such as: grounded, open or shorted. The FMI is the code which is most often misunderstood. An expanded generic description of each FMI code is given in the paragraphs that follow.
FMI 00 - Data Valid But Above Normal Operating Range. Every electronic control system sets a high limit for the "expected" operating range of a signal. The limit includes over ranges like high converter temperatures. A sensor that is still working but sending a signal above the expected limit will cause the FMI 00 code to be stored. Example - A certain pulse-width modulated (PWM) sensor is not expected to generate a valid signal over 80 percent duty cycle. If a sensor generates an 81 percent duty cycle, it is still working but is now above the expected signal limits.
FMI 01 - Data Valid But Below Normal Operating Range. Every electronic control system sets a low limit for the "expected" operating range of a signal. The limit includes under ranges like low engine oil pressure. A sensor that is still working but sending a signal below the expected limit will cause the FMI 01 code to be stored. Example - Most pulse-width modulated (PWM) sensors are not expected to generate a valid signal less than 5 percent duty cycle. If a sensor generates a 3 percent duty cycle, it is still working but is now less than the expected signal limits.
FMI 02 - Data Erratic, Intermittent Or Incorrect. Signal data from a component is present. Then the signal is either gone, unstable or invalid as recognized by the electronic control doing