CONTROL GP-EMS ELECTRONIC 9X7801 - Caterpillar

Illustration 1 g01285461Specification
This test measures the voltage drop of the coil (R) for the starter solenoid "PULL-IN". The voltage drop is measured between test point (2) and test point (4). Test point (2) is the positive contact and test point (4) is the negative contact.A voltage drop will cause the indicator lamp for the starter solenoid power circuit to turn ON. The voltage drop must be larger than 1.00 0.15 volts. The lamp turned ON in order to indicate a defect. A defect may be indicated only during "Test Step B, Crank".The possible causes of this condition are listed:
Alternator circuit breaker with excessive voltage drop
Start relay with excessive voltage dropNote: The alternator circuit breaker or the start relay may have an excessive voltage drop that is within specified range.Information for Other Circuits
The starter solenoid has two coils. The "PULL-IN" coil is coil (R). The "HOLD-IN" coil is coil (S). Both of the coils will receive power when the start relay closes. Battery voltage is applied to the high end of both coils at test point (4). The "LOW" end of the coil (S) is permanently grounded to the ground post of the starter.The grounding for the low end of coil (R) is momentary. The grounding takes place through the direct current resistance of the starter. The contacts of the solenoid close after the magnetic force is built in both coils. The temporary ground is removed from the coil (R) and battery voltage is applied to both ends.The solenoid closes. The solenoid is closed by the coil (R) and coil (S).Coil (W) is out of the circuit since a battery voltage is present on both ends of the coil. The voltage across the "PULL-IN" coil is nearly zero. It is possible that test point (4) is more negative than test point (2). If test point (4) is more negative than test point (2) by one or more volts, the current flows backward. The current flows backward through the "PULL-IN" coil and the solenoid releases.Test point (2) grounds the "PULL-IN" coil when the solenoid releases. The solenoid releases several times in a second. The contacts are burned to an open condition. The contacts become burned unless the problem is found. Replacing the solenoid returns the machine to work. Replacing the solenoid does not fix the problem.Resolving the Problem
During the cranking of the engine, the voltage drop is incorrect. The voltage drop that is across test point (1) and test point (4) is greater than the voltage drop that is across test point (1) and test point (2). The analyzer shows that the alternator circuit breaker and the start relay are within the specifications. Replacing one or both of the components can reduce the voltage drop to an acceptable range between test point (1) and test point (2). The harness connectors can have an effect on the test of the circuit. For more information on the circuit, see the complete System Schematic for the machine that is being serviced. The lamp