The master ECM contains the logic and the outputs for starting the engine. The logic for starting the engine is customer programmable. The logic responds to inputs from the following components: engine control switch, emergency stop switch, remote start switch, data link and other inputs.
Logged diagnostic codes provide a historical record. Before you begin this procedure, use the Caterpillar Electronic Technician (ET) to print the logged codes to a file.
The most likely causes of the diagnostic code are a poor electrical connection or a problem in a wiring harness. The next likely cause is a problem with a starter motor magnetic switch. The least likely cause is a problem with the master ECM.
The troubleshooting procedure may generate additional diagnostic codes. Keep your mind on correcting the cause of the original diagnostic code. Clear the diagnostic codes after the problem is resolved.
Electric Start
The master ECM supplies +battery voltage to two magnetic switches when the logic determines that it is necessary. Each magnetic switch provides +battery voltage to a solenoid on an electric starting motor.
The master ECM removes the voltage when the crank terminate relay is energized. The voltage is also removed if the customer programmable "Overcrank Time" has expired.
Air Start
The master ECM supplies +battery voltage to the air start relay when the logic determines that it is necessary. The master ECM removes the voltage when the crank terminate relay is energized. The voltage is also removed if the customer programmable "Overcrank Time" has expired.
If the engine is equipped with a prelubrication system, an air start may not occur until the prelubrication is complete. If there is a problem with the prelubrication system, the air start may not occur. There are no diagnostics for the prelubrication system. Refer to Systems Operation, Testing and Adjusting, "Air Starting System (Starting with an Air Prelube Pump)".
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| Illustration 1 | g00994427 |
Schematic for the electric starting system | |
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| Illustration 2 | g00994433 |
Schematic for the air starting system | |
Test Step 1. Inspect the Electrical Connectors and Wiring
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
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| Illustration 3 | g00902634 |
Terminal box for the master ECM (1) J2/P2 connectors for the master ECM (2) J14/P14 connectors for the harness from the starting system (3) 16 amp circuit breaker | |
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| Illustration 4 | g00993943 |
(4) Junction box for the starter motor magnetic switches | |
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| Illustration 5 | g00994436 |
Junction box for the starter motor magnetic switches (5) Magnetic switches (6) Connections for the magnetic switches | |
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| Illustration 6 | g00994353 |
Typical air start relay and connector (7) Air start relay (8) Connector for the air start relay | |
- Thoroughly inspect the following connectors and the wiring harnesses for the connectors:
- Master ECM J2/P2 connectors
- J14/P14 connectors
- Connectors for the air start relay (if equipped)
- Connections for the starter motor magnetic switches (if equipped)
- Check the torque of the Allen head screw for the ECM connectors. The proper torque is 6 ± 1 N·m (55 ± 9 lb in).
- Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit for the starter motor magnetic switches.
Show/hide table
Illustration 7 g00993907
Harness side of the master ECM P2 connector
(P2-10) Start command
(P2-20) Return for the start command
Show/hide table
Illustration 8 g01022124
(9) P14 connector for the harness from the starting system
(P14-A) Start command
(P14-B) Return for the start command
- Check the harness and wiring for abrasion and pinch points from the starting system to the master ECM.
- Master ECM J2/P2 connectors
Note: For the following steps, refer to Troubleshooting, "Inspecting Electrical Connectors".
Expected Result:
All connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points.
Results:
- OK - The components are in good condition with proper connections. Proceed to Test Step 2.
- Not OK - The components are not in good condition and/or at least one connection is improper.
Repair: Perform the necessary repairs, when possible. Replace parts, if necessary.
STOP
Test Step 2. Check for Diagnostic Codes
- Connect Cat ET to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".
- Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.
- Wait for 30 seconds and use Cat ET to check for an active "444-05 Start Relay open circuit" diagnostic code.
If there is an active "444-05 Start Relay open circuit" diagnostic code, proceed to the "Results" for this Test Step. Otherwise, continue this procedure.
Note: The "444-05 Start Relay open circuit" diagnostic code can only be detected when the output for the start command is OFF. The output is normally OFF when the engine control is in the STOP mode or when the crank terminate relay is energized.
- Use Cat ET to check the logged diagnostic codes. If there is a "444-06 Start Relay short to ground" diagnostic code, clear the code.
- To prevent the engine from starting, shut the gas supply OFF.
- Set the engine control to the START mode for at least six seconds. Then set the engine control to the STOP mode.
Note: The "444-06 Start Relay short to ground" diagnostic code can only be detected when the output for the start command is ON. The output is normally ON when the engine control is set from the "STOP" mode to the "START" mode. The output remains ON until the crank terminate relay is energized.
- Use Cat ET to look for a logged "444-06 Start Relay short to ground" diagnostic code again.
Expected Result:
When the engine control was in the STOP mode, there was no active "444-05 Start Relay open circuit" diagnostic code.
After the engine was cranked, there was no logged "444-06 Start Relay short to ground" diagnostic code.
Results:
- OK - No diagnostic codes were activated. The output for the start command seems to be OK at this time. The initial diagnostic code was probably caused by a poor electrical connection.
Repair: If there is an intermittent problem that is causing the codes to be logged, refer to Troubleshooting, "Inspecting Electrical Connectors".
STOP
- Not OK ("444-05 Start Relay open circuit" diagnostic code) - A "444-05 Start Relay open circuit" diagnostic code was activated. This can be caused by an actual open circuit or by a short circuit to the +battery side. If the engine is equipped with an air starting system, proceed to Test Step 3. If the engine is equipped with an electric starting system, proceed to Test Step 9.
- Not OK ("444-06 Start Relay short to ground" diagnostic code) - After the engine was cranked, a "444-06 Start Relay short to ground" diagnostic code was activated. If the engine is equipped with an air starting system, proceed to Test Step 7. If the engine is equipped with an electric starting system, proceed to Test Step 9.
Test Step 3. Check for a Short Circuit to the +Battery Side
- Make sure that no combustible gas is present in the surrounding atmosphere.
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Gaseous fuel is present. Personal Injury or Death can result from an open flame or spark igniting the gaseous fuel causing an explosion and/or fire. Always use a gas detector to determine the presence of gaseous fuel when maintaining and servicing. Contact you local gas provider immediately for assistance in the event of a leak. |
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Note: Open sparks can be generated during this test.
- Ensure that the engine control is in the STOP mode.
- Disconnect the connector from the air start relay. Then reconnect the connector. Listen for an audible click from the relay.
If the ambient noise is too loud, touch the air start relay when the relay is reconnected in order to feel the vibration. The relay will vibrate when the relay is de-energized and energized.
Expected Result:
There is no audible click and/or vibration when the air start relay is disconnected and reconnected. The relay is not energized when the engine control is in the STOP mode.
Results:
- OK - There is no audible click and/or vibration when the air start relay is disconnected and connected. There is no short circuit to the +battery side. There is an open circuit. Proceed to Test Step 4.
- Not OK - There is an audible click and/or vibration when the air start relay is disconnected and connected. The relay is receiving power when the engine control is in the STOP mode. Proceed to Test Step 6.
Test Step 4. Create a Short Circuit in order to Check for an Open Circuit
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- Disconnect the harness connector from the air start relay.
- Install a jumper wire into the two terminals of the harness connector for the air start relay.
- Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.
- Wait for 30 seconds and use the "Active Diagnostic" screen of Cat ET to look for a "444-05 Start Relay open circuit" diagnostic code.
Expected Result:
A "444-05 Start Relay open circuit" diagnostic code was not activated when the jumper wire was installed.
Results:
- OK - A "444-05 Start Relay open circuit" diagnostic code was not activated when the jumper wire was installed. The master ECM detected the short circuit. The harness and the master ECM are OK. There is a problem with the air start relay.
Repair: Perform the following procedure:
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- Remove the jumper wire from the harness connector.
- Inspect the relay's connector and the harness connector for the relay. Check for damage, for moisture, and for corrosion.
- Make repairs, as needed.
STOP
- Not OK - A "444-05 Start Relay open circuit" diagnostic code was activated when the jumper wire was installed. The master ECM did not detect the short circuit. Proceed to Test Step 5.
Test Step 5. Check the Master ECM
- Ensure that the engine control is in the OFF/RESET mode and that the 16 amp circuit breaker is OFF.
- Use a 151-6320 Wire Removal Tool to remove terminals P2-10 and P2-20.
- Install a jumper wire into terminals P2-10 and P2-20. Pull on the jumper wire in order to verify proper installation.
- Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.
- Wait for 30 seconds and use the "Active Diagnostic" screen of Cat ET to look for an active "444-05 Start Relay open circuit" diagnostic code.
Expected Result:
There is no active "444-05 Start Relay open circuit" diagnostic code.
Results:
- OK - When the jumper wire was installed, there was no active "444-05 Start Relay open circuit" diagnostic code. The master ECM detects the jumper wire at the P2 connector. However, the master ECM did not detect the jumper wire at the relay's connector. There is a problem with the wiring. The problem could be between the P2 connector and the J14 connector. Alternatively, the problem could be in the P14 connector or the wiring that is connected to the P14 connector.
Repair: Perform the following procedure:
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- Use a 151-6320 Wire Removal Tool to remove the jumper wire from the P2 connector.
- Reinstall terminals P2-10 and P2-20. Pull on the wires in order to verify proper installation of the terminals.
- Repair the harness, when possible. Replace the harness, if necessary.
STOP
- Not OK - When the jumper wire was installed, a "444-05 Start Relay open circuit" diagnostic code was activated. The master ECM did not detect the jumper wire. There is a problem with the master ECM.
Repair: Perform the following procedure:
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- Remove the jumper wire from the P2 connector.
- Reinstall terminals P2-10 and P2-20. Pull on the wires in order to verify proper installation of the terminals.
STOP
Test Step 6. Create an Open Circuit in Order to Check for a Short Circuit
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- Use a 151-6320 Wire Removal Tool to remove terminals P2-10 and P2-20.
- Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.
- To prevent the engine from starting, shut OFF the main gas supply.
- Set the engine control to the START mode for at least six seconds. Then set the engine control to the STOP mode.
Expected Result:
There is no audible click and/or vibration when the relay is disconnected and reconnected. The relay is not energized when the engine control is in the STOP mode.
Results:
- OK - When the master ECM was connected, the relay was receiving power. When the master ECM was not connected, the relay was not receiving power. There may be a problem with the master ECM.
Repair: Perform the following procedure:
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- Reinstall terminals P2-10 and P2-20. Pull on the wires in order to verify proper installation of the terminals.
STOP
- Not OK - When the master ECM was connected, the relay was receiving power. When the master ECM was not connected, the relay was still receiving power. There is a problem with the wiring.
The problem could be between the P2 connector and the J14 connector. Alternatively, the problem could be in the P14 connector or the wiring that is connected to the P14 connector.Repair: Repair the harness, when possible. Replace the harness, if necessary.
STOP
Test Step 7. Create an Open Circuit at the Air Start Relay
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- Disconnect the harness connector from the air start relay.
- Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.
- To prevent the engine from starting, shut OFF the main gas supply.
- Set the engine control to the START mode for at least six seconds. Then set the engine control to the STOP mode.
Note: The "444-06 Start Relay short to ground" diagnostic code can only be detected when the output for the start command is ON. The output is normally ON when the engine control is set from the STOP mode to the START mode. The output remains ON until the crank terminate relay is energized.
- Use Cat ET to look for a logged "444-06 Start Relay short to ground" diagnostic code again.
Expected Result:
A "444-06 Start Relay short to ground" was not activated.
Results:
- OK - A "444-06 Start Relay short to ground" diagnostic code was not activated when the air start relay was disconnected. There is a problem with the air start relay.
Repair: Perform the following procedure:
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- Remove the jumper wire from the connector.
- Inspect the connectors for the air start relay. Check for damage, for moisture, and for corrosion.
- Make repairs, as needed.
STOP
- Not OK - A "444-06 Start Relay short to ground" diagnostic code was activated when the air start relay was disconnected. The air start relay is OK. Proceed to Test Step 8.
Test Step 8. Check the Master ECM
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- Use the 151-6320 Wire Removal Tool to remove terminals P2-10 and P2-20.
- Switch the 16 amp circuit breaker ON. Set the engine control to the STOP mode.
- To prevent the engine from starting, shut OFF the main gas supply.
- Set the engine control to the START mode for at least six seconds. Then set the engine control to the STOP mode.
Note: The "444-06 Start Relay short to ground" diagnostic code can only be detected when the output for the start command is ON. The output is normally ON when the engine control is set from the STOP mode to the START mode. The output remains ON until the crank terminate relay is energized.
- Use Cat ET to look for a logged "444-06 Start Relay short to ground" diagnostic code again.
Expected Result:
The "444-06 Start Relay short to ground" diagnostic code was not activated.
Results:
- OK - When the wiring was disconnected from the master ECM, a "444-06 Start Relay short to ground" diagnostic code was not activated. There is a problem with the wiring. The problem could be between the P2 connector and the J14 connector. Alternatively, the problem could be in the P14 connector or the wiring that is connected to the P14 connector.
Repair: Perform the following procedure:
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- Reinstall terminals P2-10 and P2-20. Pull on the wires in order to verify proper installation of the terminals.
- Repair the harness, when possible. Replace the harness, if necessary.
STOP
- Not OK - When the wiring was disconnected from the master ECM, a "444-06 Start Relay short to ground" diagnostic code was activated. There seems to be a problem with the master ECM.
Repair: Perform the following procedure:
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- Reinstall terminals P2-10 and P2-20. Pull on the wires in order to verify proper installation of the terminals.
STOP
Test Step 9. Inspect the Inside of the Junction Box
- Disconnect the +24 V power supply from the engine.
- Remove screws (1) in order to open the junction box.
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| Illustration 9 | g00994375 |
Junction box (1) Screws | |
- Inspect the inside of the junction box. Check for moisture and for corrosion. Verify that each electrical connection inside the junction box is securely connected.
Expected Result:
The inside of the junction box does not have moisture or corrosion. All of the electrical connections inside the junction box are securely connected.
Results:
- OK - The inside of the junction box does not have moisture or corrosion. All of the electrical connections inside the junction box are securely connected. Proceed to Test Step 10.
- Not OK - The inside of the junction box has moisture or corrosion and/or there is a loose electrical connection.
Repair: Perform the necessary repairs, when possible. Replace parts, if necessary.
STOP
Test Step 10. Check for an Open Circuit
- Disconnect the P1 connector.
- Use a multimeter to check for an open circuit between the points that are listed in Table 1:
Show/hide table
Table 1 Points to Check for an Open Circuit Point Point P2-20 P1-55 (+battery) P2-10 P1-55 (+battery) Each coil terminal (1) on each magnetic switch P1-55 (+battery)
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| Illustration 10 | g00994444 |
Internal view of the junction box (1) Coil terminals on the magnetic switches | |
Expected Result:
All of the measurements are an open circuit.
Results:
- OK - All of the measurements are an open circuit. There is not a short circuit to the +battery. Reconnect the P1 connector. Proceed to Test Step 11.
- Not OK - At least one measurement is not an open circuit. There is a short circuit to the +battery.
Repair: Reconnect the P1 connector. Repair the wiring, when possible. Replace parts, if necessary.
STOP
Test Step 11. Check the Wiring for Continuity
- Use a multimeter to check for continuity between the terminations that are listed in Table 2:
Show/hide table
Table 2 Terminations to Check for Continuity Termination Termination P2-10 The connection for the magnetic switch that is connected to wire "A310-RD" P2-20 The connection for the magnetic switch that is connected to wire "A310-BK"
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| Illustration 11 | g00994448 |
Internal view of the junction box | |
Expected Result:
All of the measurements are less than two ohms.
Results:
- OK - All of the measurements are less than two ohms. The wiring between the ECM and the magnetic switches has continuity. Reconnect the P1 connector. Proceed to Test Step 12.
- Not OK - At least one measurement is more than two ohms. There is an open circuit in at least one of the wires for the electric starting system.
Repair: Reconnect the P1 connector. Repair the wiring, when possible. Replace parts, if necessary.
STOP
Test Step 12. Check the Coils for the Magnetic Switches
- Disconnect the A310-BK wire and the A310-RD wire from the top magnetic switch.
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| Illustration 12 | g00994452 |
Internal view of the junction box (1) Bus bars | |
- Remove bus bars (1) .
- Use a multimeter to measure the resistance of the coil for each magnetic switch.
Expected Result:
The resistance of each coil is between 16 and 20 ohms.
Results:
- OK - The resistance of each coil is between 16 ohms and 20 ohms. The coil resistance for each magnetic switch is correct.
Repair: Perform the following procedure:
- Reinstall the bus bars.
- Reconnect the A310-BK wire and the A310-RD wire to the top magnetic switch. Be sure to connect the wires to the appropriate terminals.
- Install a lockwasher and a nut onto each stud. Torque the nuts to 1.70 ± 0.25 N·m (15 ± 2 lb in).
- Close the terminal box's cover and secure the cover with two screws.
- Reconnect the +24 V power supply to the engine.
Proceed to Test Step 13.
- Not OK - The resistance of a coil is not between 16 ohms and 20 ohms. The resistance of the coil is incorrect.
Repair: Replace the magnetic switch. Verify that the original problem is resolved.
STOP
Test Step 13. Check the Operation of the Master ECM
- Use a 151-6320 Wire Removal Tool to remove terminals P2-10 and P2-20.
- Switch the 16 amp circuit breaker ON.
Note: The "444-05 Start Relay open circuit" diagnostic code can only be detected when the output for the start command is OFF. The output is normally OFF when the engine control is in the STOP mode or when the crank terminate relay is energized.
- Set the engine control to the STOP mode.
A "444-05 Start Relay open circuit" diagnostic code should be activated.
- Set the engine control to the OFF/RESET mode. Switch the 16 amp circuit breaker OFF.
- Reinstall terminals P2-10 and P2-20. Pull on the wires in order to verify proper installation of the terminals.
- Switch the 16 amp circuit breaker ON.
- Set the engine control to the STOP mode.
A "444-05 Start Relay open circuit" diagnostic code should not be activated.
- Set the engine control to the START mode for at least six seconds. Look for a "444-06 Start Relay short to ground" diagnostic code.
A "444-06 Start Relay short to ground" diagnostic code should not be activated.
Note: The "444-06 Start Relay short to ground" diagnostic code can only be detected when the output for the start command is ON. The output is normally ON when the engine control is set from the STOP mode to the START mode. The output remains ON until the crank terminate relay is energized.
Expected Result:
When the wires were not connected, the ECM activated an "444-05 Start Relay open circuit" code. When the wires were connected, the ECM did not activate a "444-06 Start Relay short to ground" code.
Results:
- OK - The ECM appears to be operating correctly. The initial diagnostic code was probably caused by a poor electrical connection.
Repair: If there is an intermittent problem that is causing the codes to be logged, refer to Troubleshooting, "Inspecting Electrical Connectors".
STOP
- Not OK - The ECM did not operate correctly. There may be a problem with the master ECM.
Repair: It is unlikely that the master ECM has failed. Exit this procedure and perform this procedure again. If the problem is not resolved, perform the following steps:Temporarily install a new master ECM. Refer to Troubleshooting, "Replacing the ECM".If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the original ECM. Refer to Troubleshooting, "Replacing the ECM".
STOP