1999/03/15 Caterpillar

All Caterpillar Machines And Engines Equipped With Prelub

Introduction

Prelub uses the starter motor to run an oil pump which primes the engine oil system before starting. This information applies to machines using the Caterpillar Prelub system that is equipped with the 125-6935, 139-1585, and 140-3108 Timer Assemblies. There are other prelubrication systems that are installed on machines made by Caterpillar, but this Special Instruction is not applicable to these other systems.

Normal Operation

1. Turn the key switch to the CRANK position and hold the switch in the CRANK position.

2. The starter motor runs in Prelub Mode. The motor spins but the flywheel is not engaged. The starter motor runs for 3 to 45 seconds until oil pressure reaches between 27 kPa (4 psi) and 48 kPa (7 psi). The oil pressure is measured at the Prelub oil pressure switch.

3. The key switch is still held in the CRANK position. The starter is delayed for 3 seconds and spinning stops.

4. The starter then engages the flywheel and the engine is cranked normally.

Basic Operation Of The Prelub Timer

Basic Prelub Electrical Schematic

Circuitry Of The Timer

(1) Relay Control.

(2) 3 Second Delay Control.

Power from the keyswitch is supplied to contact 1 of the timer when the keyswitch is in the CRANK and RUN positions. Contact 1 supplies power to the electronic circuits that are inside the timer. Contact 2 connects through the wiring harness to the ground terminal on the starter solenoid. When the Prelub oil pressure switch detects pressure less than 4 psi, contact 4 is connected to ground. Power from contact 3 (CRANK) then passes through the normally closed internal relay. The Prelub mag switch is then energized. When the Prelub mag switch closes, current flows to the motor terminal on the starter solenoid. The starter motor is allowed to run without engaging the starter drive.

When the Prelub starter motor runs, the Prelub pump will pressurize the oil system. The Prelub pump draws oil from the engine oil pan. The oil is then pumped into the engine oil system through the oil hoses of the Prelub system. The oil pressure is measured at the Prelub oil pressure switch. When the oil pressure exceeds 27 kPa (4 psi) to 48 kPa (7 psi), the timer turns off the Prelub mag switch. The starter motor will stop turning. The timer will wait for 3 seconds. Then, an internal relay in the timer will allow power from the key switch (contact 3) to pass through contact 5 on the timer. Now, the starter will crank normally. If the key switch is turned OFF for less than 2 minutes before another crank attempt, Prelub will not activate. The starter will crank normally. The timer is located on the electric circuit between the key switch and the transmission ECM. The timer is also located on any electric circuits that might exist between the key switch and other controls or devices that prevents cranking.

Initial Troubleshooting Procedure

NOTE: During Prelub Mode, the starter motor runs but the drive is disengaged from the engine. The engine will not crank in this mode but the starter motor will be spinning. The battery disconnect switch must be ON for all testing unless there is a note with other instructions. Batteries must be fully charged.

The key must be in the OFF position for more than 2 minutes between tests that involve the Prelub Mode.

If you are testing alone, use the "Peak hold" feature on your DMM in order to record the voltage readings from tests below. Turn on the DMM and turn on the "peak hold" or record feature. See the instructions for your DMM. Take the reading per the instructions in each test below. The "Peak hold" mode on the DMM must be reset before each step. Connections must be made prior to entering "peak hold mode".

NOTE: This Special Instruction can be used for the 4Q-5450 Timer Switch Assembly if the following changes are noted:

* The 4Q-5450 Timer Switch Assembly does not have a 113 circuit (contact 1). A yellow wire is in contact 1 of the connector but this wire is not used.

* The negative wire to the Prelub mag switch is green. The Prelub mag switch is mounted to the timer on this type.

* Contact 5 on both systems goes to the starting circuit. The wire color on the 4Q-5450 Timer Switch Assembly (contact 5) is white and black rather than yellow on the other timers.

* The delay of 2 minutes (key OFF) to inhibit Prelub Mode does not apply to the 4Q-5450 Timer Switch Assembly.

Test 1

1. Check Prelub Mag Switch.

a. Connect a DMM to the 2 small terminals on the Prelub mag switch. Connect the negative lead of the DMM to the negative terminal on the Prelub mag switch. Connect the positive lead of the DMM to the positive terminal on the Prelub mag switch. On newer Prelub timers, the red/white wire is the negative side of the coil on the Prelub mag switch. On all Prelub timers, the lead from the negative coil on the Prelub mag switch comes out of the timer. The wire is right next to the black wire (contact 4).

b. Turn on the DMM and set the DMM to "DC volts". Hold the key in the CRANK position for at least 5 seconds.

Expected Result: The DMM reads at least 20 volts while the key is in the CRANK position. The DMM should read 10 volts for 12 volt systems.

Results:

* Yes - The Prelub timer is attempting to enter Prelub Mode. The oil pressure switch is properly grounded, and power is available to the timer. Go to 4.

* No - The Prelub mag switch is not being energized. Proceed to 2.

2. Check Ground Circuit.

a. Insert a multimeter probe into the back of contact 2 (ground). Insert the probe on the side of the 6-pin connector that goes to the timer.

b. Connect the multimeter probe to the positive terminal on the DMM. Connect the negative lead to a good ground.

c. Turn on the DMM, and set the DMM to DC volts. Hold the key in the CRANK position for at least 5 seconds.

Expected Result: The DMM reads at least 1 volt while the key is in the CRANK position. The DMM should read 0.5 volts for 12 volt systems.

Results:

* Yes - Ground circuit (200) has high resistance. Check the following items for damage, corrosion, or poor connections: The ground wire from the Prelub 6-pin connector (contact 2), the ground terminal for the starter solenoid, the engine to frame grounds, and the negative battery post to engine ground. Make sure that the main disconnect switch is turned ON. Make sure that the main disconnect switch is working properly by checking continuity. Repair the problems with the circuit and retest the system.

* No - Proceed to 3.

3. Check For Power From The Keyswitch.

a. Insert a multimeter probe into the back of contact 3 (CRANK). Insert the probe on the side of the 6-pin connector that goes to the timer.

b. Connect the multimeter probe to the positive terminal on the DMM. Connect the negative lead to a good ground.

c. Turn on the DMM, and set the DMM to DC volts. Hold the key in the CRANK position for at least 5 seconds.

Expected Result: The DMM reads at least 20 volts while the key is in the CRANK position. The DMM should read at least 10 volts for 12 volt systems.

Results:

* Yes - Proceed to 4.

* No - There is no power from the key switch on circuit 337 of the machine wiring. Check the wiring from the key switch to the Prelub 6-pin connector. Check for wires that are loose, corroded or damaged. Check the key switch for proper operation. Check related fuses and breakers. Repair the problems with the circuit and retest the system.

4. Check For Power To the Prelub Mag Switch.

a. Connect the negative lead of the DMM to a good ground.

b. Set the DMM to DC volts. Touch the positive lead of the DMM to one of the large terminals on the Prelub Mag Switch.

c. Read the DMM. Then touch the positive lead of the DMM to the other large terminal on the Prelub Mag Switch.

Expected Result: One of the terminals has system voltage.

Results:

* Yes - Note this as the battery terminal on the Prelub Mag Switch. Proceed to 6.

* No - There is no power to the Prelub Mag Switch. Proceed to 5.

5. Check Harness.

a. Connect the negative lead of the DMM to a good ground. Touch the positive lead of the DMM to the B+ terminal that is on the starter solenoid.

b. Turn on the DMM and set the DMM to DC volts. Check for system voltage.

Expected Result: The terminal has system voltage.

Results:

* Yes - There is an open circuit in the Prelub wiring between the battery terminal of the starter solenoid and the Prelub Mag Switch (circuit 101). Repair the wiring from the starter solenoid to the Prelub Mag Switch. Retest the system.

* No - Repair the open circuit in the battery to starter wiring. The open circuit could be caused by one of the following problems: loose connections, broken wires, corroded wires, or a faulty disconnect switch. Ensure that the main disconnect switch is working properly. Ensure that the wiring from the battery to the frame and engine grounds is good. See starting system diagnostic procedures to continue.

6. Check Prelub Mag Switch.

a. Connect the positive lead of the DMM to the motor terminal on the Prelub Mag Switch. The motor terminal is the large terminal opposite the battery terminal that was found in 4.

b. Turn on the DMM and set the DMM to "DC volts".

c. Hold the key in the CRANK position for 5 seconds.

Expected Result: The DMM reads at least 20 volts while the key is in the CRANK position. The DMM should read at least 10 volts for 12 volt systems.

Results:

* Yes - There is an open circuit in the large Prelub wire from the Prelub Mag Switch to the starter motor terminal (circuit 301). Proceed to 7.

* No - Replace the Prelub Mag Switch and retest the system.

7. Check Harness.

a. Connect the positive lead of the DMM to the motor terminal (large terminal toward motor) on the starter solenoid. Connect the ground lead of the DMM to a good ground.

b. Turn on the DMM and set the DMM to "DC volts".

c. Hold the key in the CRANK position for 5 seconds.

Expected Result: The DMM reads at least 20 volts while the key is in the CRANK position. The DMM should read at least 10 volts for 12 volt systems.

Results:

* Yes - If the starter motor does not run, replace the starter motor and retest the system.

* No - Repair or replace the Prelub wire (301) from the Prelub Mag Switch to the motor terminal on the starter solenoid and retest the system.

Test 2

1. Check Harness.

a. Insert a multimeter probe into the back of contact 4 (oil pressure switch). Insert the probe on the side of the 6-pin connector that goes to the timer.

b. Connect the multimeter probe to the positive terminal on the DMM. Connect the negative lead to a good ground.

c. Turn on the DMM and set the DMM to "DC volts".

d. Hold the key in the CRANK position for at least 5 seconds.

Expected Result: The DMM reads at least 1 volt while the key is in the CRANK position. The DMM should read at least 0.5 volts for 12 volt systems.

Results:

* Yes - The Prelub oil pressure switch circuit is not grounded with the engine off. This condition may be caused by one of the following problems: An open circuit in the wiring, poor wiring connections, or a faulty Prelub oil pressure switch. Proceed to 2.

* No - Replace Prelub timer and retest the system.

2. Check Oil Pressure Switch.

Leave the DMM connected as it was above.

a. Make sure that all of the electrical connections of the Prelub system are properly connected.

b. Disconnect the Prelub oil pressure switch. Connect a jumper wire between the 2 terminals in the connector for the oil pressure switch.

c. Turn on the DMM and set the DMM to "DC volts".

d. Hold the key in the CRANK position for at least 5 seconds.

NOTE: If the starter motor now runs in Prelub Mode, replace the oil pressure switch.

Expected Result: The DMM reads at least 1 volt while the key is in the CRANK position. The DMM should read at least 0.5 volts for 12 volt systems.

Results:

* Yes - The oil pressure switch wiring has an open circuit. Proceed to 3.

* No - Make sure the terminals in the Prelub oil pressure switch connector are clean and in good condition. Replace the Prelub oil pressure switch and retest the system.

3. Check Harness.

Leave the DMM connected from the previous step.

a. Connect a jumper wire from the pink wire (circuit A447) at the Prelub oil pressure switch connector to a good ground.

b. Turn on the DMM and set the DMM to "DC volts".

c. Hold the key in the CRANK position for at least 5 seconds.

Expected Result: The DMM reads at least 2 volt while the key is in the CRANK position. The DMM should read at least 0.5 volts for 12 volt systems.

Results:

* Yes - Repair the open circuit wire (A447) between the Prelub timer and the Prelub oil pressure switch connector. Check the connections for corrosion, or damaged pins. Repair the problems with the circuit and retest the system.

* No - An open circuit exists between the Prelub oil pressure switch connector and the starter solenoid ground (circuit 200). Repair the problems with the circuit and retest the system.

Test 3

2. Check For Prelub oil pressure switch Operation.

a. Disconnect the connector for the Prelub oil pressure switch.

b. Turn the key to the CRANK position and hold the key for more than 10 seconds.

Expected Result: The starter cranks the engine after a delay (3 seconds).

Results:

* Yes - The Prelub oil pressure switch is not working properly or the oil pressure to the Prelub oil pressure switch never exceeds between 27 kPa (4 psi) and 48 kPa (7 psi). Proceed to 2.

* No - The wire from the Prelub timer connector is shorted to ground or the Prelub timer is faulty. Proceed to 7.

2. Check Oil Pressure.

a. Remove the oil pressure switch from the engine.

b. Connect an oil pressure gauge to the port on the engine for the oil pressure switch.

c. Connect a jumper wire between the terminals in the connector of the Prelub oil pressure switch.

d. Turn the key to the CRANK position and observe the oil pressure. Hold the key in the CRANK position until one of the following events occurs: the oil pressure is 48 kPa (7 psi), or wait until 45 seconds pass.

Expected Result: The oil pressure exceeds 48 kPa (7 psi).

Results:

* Yes - Replace the Prelub oil pressure switch and retest the system.

* No - Proceed to 3.

3. Check Oil In The Engine.

Check that the engine oil pan is filled to the proper level with good, clean oil that is not contaminated.

Expected Result: The oil is good.

Results:

* Yes - Proceed to 4.

* No - Fill to proper level with good oil, or change oil as needed, and retest the system. If the oil is contaminated, determine the root cause in order to prevent a recurrence.

4. Check Prelub Pump Output.

a. Remove the pressure hose (outlet) from the Prelub pump.

b. Connect a hose from the pressure port to a suitable container and restrain the hose from coming out of the container.

c. Turn the key to the CRANK position until one of the following events occurs: the oil pressure is 48 kPa (7 psi), or wait until 45 seconds pass.

Expected Result: Oil flows from the hose.

Results:

* Yes - Proceed to 6.

* No - Proceed to 5.

5. Check Oil Suction Tube.

Check the suction hose for air leaks and restrictions. Make sure that the end of the suction tube is immersed in oil.

Expected Result: There are air leaks or restrictions.

Results:

* Yes - Repair leaks or restrictions and retest the system.

* No - Replace the Prelub starter motor.

6. Check Pressure Hose And Check Valve.

Check that the Prelub oil check valve is properly installed. The arrow must be pointing in the direction of oil flow. Check the pressure hose for restrictions.

Expected Result: The check valve was installed properly and the hoses are free of restrictions.

Results:

* Yes - The oil system in the engine has a large internal leak, blocked oil passages, or excessive engine bearing wear. Repair the system and retest the system.

* No - Install the check valve properly and/or repair pressure hose restrictions as needed and retest the system.

7. Check Harness To Prelub oil pressure switch.

a. Remove pin 4 (black wire) from the Prelub 6-pin connector.

b. Reconnect the connector and hold the key in the CRANK position for at least 10 seconds. If the engine cranks after a delay, release the key.

Expected Result: The starter has a delay. Then, the starter cranks the engine.

Results:

* Yes - Repair the short to ground in the wire (circuit A447) from contact 4 to the Prelub oil pressure switch and retest the system. Remember to reinstall pin 4 in the 6-pin connector.

* No - Replace the Prelub timer and retest the system. Remember to reinstall pin 4 in the 6-pin connector.

Test 4

NOTE: Tapping on the Prelub Mag Switch may temporarily break the weld that is causing the contact disk to stick in the Prelub Mag Switch. Normal operation would be temporarily restored. If this occurs, replace the Prelub Mag Switch. Caterpillar does not recommend this action due to the possibility of breaking the component. Similarly, tapping on the starter solenoid may temporarily break the weld that is causing the contact disk to stick inside the starter solenoid. Normal operation would be temporarily restored. If this occurs, replace the starter solenoid. Caterpillar does not recommend this action due to the possibility of breaking the component.

1. Check Harness.

Make sure that the batteries are fully charged and make sure that the batteries are in good condition. Low cranking voltage may contribute to welding of the contact disk.

a. Turn OFF the main disconnect switch.

b. Disconnect one of the large wires from the Prelub Mag Switch.

c. Turn ON the disconnect switch.

Expected Result: The starter motor still runs.

Results:

* Yes - Turn OFF the disconnect switch. The Prelub Mag Switch or the Prelub wiring is shorted. Proceed to 2.

* No - Replace the Prelub Mag Switch and retest the system.

2. Check Harness.

a. Disconnect the Prelub wire from the motor terminal on the starter solenoid.

b. Turn ON the disconnect switch.

Expected Result: The starter motor still runs.

Results:

* Yes - The contact disk inside the starter solenoid is stuck. Replace the starter solenoid and retest the system. If the starter motor shows signs of damage replace the starter motor as well.

* No - The wiring from the Prelub Mag Switch and the starter motor is shorted. Repair the problems with the circuit and retest the system.

Test 5

NOTE: Do not use "peak hold" or "record mode" on the DMM for this test.

1. Check For Excessive Starter Current.

a. Connect a current probe (DC) around either of the large wires that are connected to the Prelub Mag Switch. Use a 9U-5795 Current Probe.

b. Turn the key to the CRANK position, and observe the current after the starter motor has run for more than 2 seconds in Prelub Mode.

Expected Result: The DMM reads at least 300 amperes while the key is in the CRANK position. The DMM should read at least 400 amperes for 12 volt systems.

Results:

* Yes - The starter current is excessive. Proceed to 2.

* No - Service and charge batteries as needed. Check Prelub wiring connections from the starter solenoid to the Prelub Mag Switch for looseness, corrosion, or hot spots. Make sure that the ground connections are good. Repair the problems with the circuit and retest the system.

2. Check For Oil Leakage.

a. Check for oil inside the starter motor.

Expected Result: Oil is present inside the starter motor.

Results:

* Yes - This could be accompanied by a Prelub pump lid gasket failure, which is an indication of a Prelub check valve failure or excessive restrictions in the Pressure hose of the Prelub system. Proceed to 3.

* No - Replace the starter motor and retest the system.

3. Pinpoint Oil Leak.

The oil could be entering from the starter nose housing, or the oil could be entering from the Prelub pump. Remove the starter and inspect the nose housing.

Results:

* Oil appears to be coming from the nose housing. Replace the starter and retest the system.

* Oil appears to be coming from the Prelub pump. Replace the starter. Replace the Prelub check valve and repair any restrictions in the pressure hose and retest the system.

Test 6

The batteries must be fully charged and the battery cables must be clean and tight before continuing.

This test can be made much quicker and easier by making a Prelub bypass connector. To make the bypass connector, obtain a 102-8805 hard-shell kit, 6 inches of 14ga wire, and two 9W-0852 terminals. Install the terminals on each end of the wire using the proper crimp tool. Insert one end of the wire in the connector in location 3 and the other in location 5. This bypass connector can now be plugged into the Prelub wiring harness in place of the timer. This will restore normal operation of the starter with no Prelub function. If the starter now works normally (less the Prelub Mode and delay) replace the Prelub timer. If the starter still chatters or does not engage, continue with the testing below starting at 2.

1. Test For Prelub Timer Fault.

NOTE: The Prelub Mode and delay will not function during this test.

a. Disconnect the Prelub timer.

b. Connect a jumper wire from contact 3 to contact 5. Be careful not to short to any other wires in the connector and do not damage the Prelub harness connector.

Expected Result: The engine cranks normally now.

Results:

* Yes - Replace the Prelub timer and retest the system.

* No - The wiring, starter relay, or starter solenoid is at fault. Proceed to 2.

2. Check Current From Keyswitch.

Leave the jumper wire or bypass connector from above in place for this test.

a. Insert a connector probe into contact 5 of the Prelub harness connector (on the harness side).

b. Turn on the DMM and set to DC volts.

c. Hold the key in the CRANK position for 3 seconds.

Expected Result: The DMM reads at least 20 volts while the key is in the CRANK position. The DMM should read at least 10 volts for 12 volt systems.

Results:

* Yes - The key switch and wiring to the Prelub timer is OK. Proceed to 3.

* No - There is insufficient current from the key switch. The key switch or related wiring or connections need repair. Repair the problems with the circuit and retest the system.

3. Check Harness.

Leave the jumper wire or bypass connector from above in place for this test.

a. Connect the positive lead from the DMM to the positive terminal on the starter relay coil.

b. Connect the negative lead to the ground terminal on the starter solenoid.

c. Hold the key in the CRANK position for 3 seconds.

Expected Result: The DMM reads at least 20 volts while the key is in the CRANK position. The DMM should read at least 10 volts for 12 volt systems.

Results:

* Yes - The Prelub system and wiring are good. The starter relay, starter solenoid, or related wiring or connections are at fault. Pinpoint fault and repair as needed.

* No - The circuit from the Prelub timer has excessive voltage drop. The circuit (307) goes through the following components: contact 5 in the Prelub connector, the transmission control, any other starter lockout system, or the starter relay coil. Check all related connections for corrosion and proper connection. Check the related wiring for damage. Verify the integrity of all starter lockout devices such as the transmission control. Repair the problems with the circuit and retest the system.

Test 7

1. Check Key ON Circuit From Keyswitch.

a. Insert a connector probe in the backside of contact 1 (circuit 113) in the Prelub timer connector.

b. Connect the multimeter probe to the positive terminal on the DMM. Connect the negative lead to a good ground.

c. Turn on the DMM and set to "DC volts".

d. Turn the key to the RUN position.

Expected Result: The DMM reads at least 20 volts while the key is in the CRANK position. The DMM should read at least 10 volts for 12 volt systems.

Results:

* Yes - Replace the Prelub timer and retest the system.

* No - The key ON circuit (113) from the key switch to the Prelub timer has a fault (high resistance or open circuit). Repair the problems with the circuit and retest the system.