SEAL-RING 8D3971 - Caterpillar

System Operation Description:This procedure covers the following diagnostic codes:
94-3 Fuel Pressure voltage high (37)
94-4 Fuel Pressure voltage low (37)
100-3 Oil Pressure voltage high (24)
100-4 Oil Pressure voltage low (24)
102-3 Boost Pressure voltage high (25)
102-4 Boost Pressure voltage low (25)
108-3 Barometric Pressure voltage high (26)
108-4 Barometric Pressure voltage low (26)
164-3 Injection Actuation Pressure voltage high (15)
164-4 Injection Actuation Pressure voltage low (15)Background InformationThe Engine Control Module (ECM) continuously creates a pull-up voltage on the signal wire for each sensor. The ECM uses this pull-up voltage in order to detect a problem in the signal circuit. When the ECM detects voltage that is above a threshold on the signal wire, the ECM activates a -3 diagnostic code. When the ECM detects voltage that is below a threshold on the signal wire, the ECM activates a -4 diagnostic code.Note: There may be a delay of 30 seconds in order for Caterpillar Electronic Technician (ET) to display an active diagnostic code. When you check for a diagnostic code, be sure to wait at least 30 seconds.The most likely cause of a code is a problem with an electrical connector or wiring. The least likely cause of a code is the ECM.108-3 Diagnostic Code and High Crankcase PressureSome atmospheric pressure sensors that are located in the engine block actually sense crankcase pressure rather than atmospheric pressure. With this type of installation, crankcase pressure of approximately 14 kPa (2 psi) can cause the 108-3 diagnostic code to be generated.Before you proceed with this test, determine whether the sensor is sensing crankcase pressure or atmospheric pressure.If the sensor is sensing crankcase pressure, connect Caterpillar Electronic Technician (ET) to the ECM and clear the diagnostic code. Do not start the engine. Maintain electrical power to the ECM. Wait at least 30 seconds for generation of the diagnostic code. Slowly wiggle the wiring for the sensor in an attempt to generate an intermittent code.If the 108-3 code is generated, continue with the functional test.If the 108-3 code is not generated, there is either a problem with high crankcase pressure or the code is intermittent, due to a loose connector or damaged wiring.A plugged crankcase breather will cause excessive crankcase pressure. Leakage of the crankshaft seal can occur. Sealing of the piston rings can be lost. This will enable crankcase blowby to further increase the crankcase pressure.If the piston rings do not seal, blowby will increase the crankcase pressure and the problem will become worse. Performance will deteriorate. The engine will have poor combustion. Deposits will build up on the pistons, on the valves, and in the cylinder heads. Downward pumping of the pistons against the increased crankcase pressure will further reduce the performance.Sticking of the pistons will also increase the crankcase pressure. If the problem is not resolved, piston seizure will result. If a problem with a piston is suspected, do not operate the engine. Inspect the cylinder liner for scoring and for scuffing. Replace the piston rings and the cylinder liner, if necessary.To eliminate crankcase pressure