This article provides instructions for Caterpillar 3406E, C-10, C-12, C-15, C-16, and C-18 truck engines that crank but will not start.

Probable Causes:

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The probable root causes are listed in order below:
Key switch
Communications between the ECM and the
Caterpillar Electronic Technician (Cat ET)
Aftermarket engine protection devices
Power to ECM
Personality Module
ECM
Electrical connections to the electronic unit
injector
Engine speed/timing signal
Engine software
Theft deterrent

Fuel supply Combustion problem Recommended Actions Perform the following diagnostic procedures in order:

1. Check the key switch.
a. Connect Cat ET to the data link connector.
b. Access the status for "Ignition Key Switch".
c. Slowly cycle the key switch ON and OFF while the status for "Ignition Key Switch"is being monitored. The status should indicate the state of the switch.
If the ECM will not communicate and the key switch is in the ON position, refer to Step 3. Note: If the Engine Shutdown Output feature isused, the status for "Ignition Key Switch"may indicate that the switch is ON even though the key switch is turned to the OFF position.

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2. Check the communications between the ECM and Cat ET.
a. Connect Cat ET to the data link connector.
b. Ensure that the key switch is in the ON position. Attempt to access one of the status screens on Cat ET.
If Cat ET indicates that the ECM will not communicate go to Step 3. If the ECM communicates go to Step 6.
Note: A new ECM has a personality module that is not programmed. A new ECM that is notprogrammed will cause this symptom. Accessing the ECM status in "WinFlash" without programmingthe personality module will cause the engine not to start or accessing the ECM status in "WinFlash"
without programming the personality module will cause the engine not to communicate. Cycling the key switch from the OFF to the ON position will correct this problem.

3. Check aftermarket engine protection devices.
These devices usually interrupt power to the ECM and the ECM will not communicate with Cat ET.
a. Check for the correct installation of the aftermarket engine protection device.
b. Check for the correct operation of the aftermarket engine protection device.

c. Verify that the ECM is receiving battery voltage.

4. Check the electrical power supply to the ECM.
a. Check the power connection of the ECM and the ground connection of the ECM.
b. Verify that the ECM is receiving battery voltage when the key switch is turned ON.
Refer to Troubleshooting, "Ignition Key Switch Circuit and Battery Supply Circuit-Test".

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5. Check the personality module.
A new ECM has a Personality Module that is not programmed. The engine will not start until the personality module has been flashed. Also, the engine will not communicate until the personality module has been flashed.

6. Check the ECM.
Before replacing the ECM, try to flash program the existing ECM. Refer to Troubleshooting.
"Flash Programming".
If the ECM is suspected of being the problem, temporarily connect a test ECM. This will show whether the problem has been resolved or the problem has not been resolved.

7. Check the electrical connections to the electronic unit injectors.
a. Ensure that the J300/P300 Electronic Unit Injector connector is fully connected andensure that the J300/P300 Electronic Unit Injector Connector is free of corrosion.
b. Check for logged diagnostic codes that are related to the injectors. Refer to the injectors are present.
Troubleshooting, "Injector Solenoid Circuit -Test"if diagnostic codes that are related to

8. Check the engine speed/timing signal.
a. Observe the engine rpm on Cat ET while the engine is being cranked.
This may require Cat ET to be powered directly by the vehicle batteries or this may require Cat ET to be powered directly by a separate power source (12 VDC). Refer to Illustration 31.

   9. Check for the correct engine software. ConnectCat ET to the service tool connector. Ensure that
252-11 Incorrect Engine Software is not active.
If the diagnostic code is present, refer to Troubleshooting, "ECM Memory-Test".
Connect Cat ET to the service tool connector.
Check for the following diagnostic codes:
224-11 Theft Deterrent Active
224-14 Theft Deterrent Active with Engine Cranking

10. Ensure that the theft deterrent (if equipped) is not active. Turn the key switch to the ON position.
Observe the display screen on the CAT ID.
If the display screen on the CAT ID indicates that the theft deterrent is enabled, the theft deterrent passwords must be entered before the engine will start.

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11. Check the fuel supply.
a. Monitor the exhaust for smoke while the engine is being cranked.
If no smoke is present, there may be a problem with the fuel quality or there may be a problem with the fuel supply.

b. Check the fuel quality. Refer to Testing andAdjusting, "Fuel Quality -Test". Also refer to Truck Performance and Driveability Diagnostic Guide, LEBT3477.
c. Check the fuel pressure. Refer to Testing and Adjusting, "Fuel System Pressure -Test".
d. Ensure that the fuel system has been primed.
Refer to Testing and Adjusting, "Fuel System Prime".
e. Check for fuel supply lines that are restricted.
f. Check the fuel filters.
g. If the temperature is below 0°℃ (32 °F), check for solidified fuel (wax).

12. Check for combustion problems.
Examples of combustion problems are shown in the following list: Outside temperatures are too cold.
Mechanical problem