1990/11/19 Caterpillar

Reference: Service Magazine; December 10, 1984; Page 4; "Starters That Remain Engaged After Engine Is Running" for All Engines With Electric Starters.

Service Magazine; April 24, 1989; Page 1; "Causes And Effects Of Low Battery Voltage On Electric Starters". Service Magazine; May 28, 1990; Page 1; "Testing The Starter On The Engine".

Reference: Special Instruction; "Use of 6V2150 Starting/Charging Analyzer Group; Form SEHS776803.

Results have shown that overspeed is the most common reason for electric starter motor failure. One symptom is "milled" drive pinion teeth which sometimes accompany the failure. The cause of such failures is almost NEVER the starter itself. The true cause is often hidden in the machine wiring. An intermittent fault can further complicate problem identification. Field returns of related electrical components suggest most often that the cause of continuous starter engagement or attempted engagement after the engine is running, comes from:

1. A stuck or intermittent key start switch.

2. Electrical leakage within the machine wiring that keeps the start relay energized after a normal startup.

The "service tool" described in this article can be fabricated in the field and used to troubleshoot any machine equipped with a Diagnostic Connector. To construct the unit, install two indicator lamps in a small box or on the dashboard where they can be seen by the operator (or service technician). Connect the indicator lamps as shown in the illustration. Use automotive grade wiring and the parts listed in the chart. Secure the wiring in place on the machine. Plug the VE connector into the Diagnostic Connector. When the "start" contacts in the key switch are closed, the indicator lamp labeled "KEY SWITCH" will light. When the "start" relay contacts close to power the starter solenoid, the indicator lamp labeled "START RELAY" will light. Both lamps will light during a NORMAL crank cycle. If either one or both lamps STAY ON after the engine starts, or TURN BACK ON anytime during the work cycle, the service technician can find the true cause of incorrect starter engagement with greater ease.

To monitor the second starter on machines equipped with two starters, add an indicator lamp for the second starter relay. Because the key switch activates both starter relays, a second "KEY SWITCH" lamp is not required. To apply this same troubleshooting tool on 12 volt machines, use appropriate indicator lamps and connect them directly to the machine electrical system. Use the REFERENCE listed in this article as a guide.

NOTE: Use extreme care when connecting the "STARTER (or optional SECOND STARTER)" lamp, as this circuit may not be protected against short circuits.

Schematic diagram of starter monitor unit. Components connected with solid lines are for machines with a single starter. Components connected with dashed lines are optional, and must be added to the circuit for machines equipped with two starters.