LAMP 3C8426 - Caterpillar

Illustration 1 g01189071
Schematic of the Circuit for the Downshift Solenoid
This diagnostic code is associated with the parking brake solenoid valve. This diagnostic code is recorded when the ECM reads the voltage of the solenoid valve circuit as being above normal. The circuit is shorted to the +battery circuit.The possible causes of this failure are listed:
The energized circuit for the solenoid valve is shorted to the +battery circuit.
The ECM has failed. This is unlikely.Note: Ensure that the diagnostic code is active.System Response:The transmission will not shift because the solenoid is ON at all times.Test Step 1. CHECK THE SOLENOID CIRCUIT FOR A SHORT TO THE + BATTERY.
Turn the key start switch and the disconnect switch to the OFF position.
Disconnect the machine harness from the solenoid valve.
Disconnect the machine harness connectors J1 and J2 from the ECM.
At machine harness connector J1 and J2, measure the resistance from the signal contact J1-12 (wire 704-GY(Grey)) to all possible sources of +battery. The possible sources of positive voltage are contacts: J1-2, J1-4, J1-6, J1-10, J1-12, J1-31, J1-88, J1-39, J1-47, J1-62, J2-3 and J2-7. Expected Result:Each resistance should be greater than 5000 ohms.Results:
YES - Each resistance is greater than 5000 ohms. The machine harness is correct. Proceed to test step 2.
NO - There is a short in the machine harness. Repair: The short is between the signal contact J1-12 (wire 704-GY(Grey)) and the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness.STOPTest Step 2. CHECK IF THE DIAGNOSTIC CODE REMAINS.
Inspect the contacts and clean the contacts of the harness connectors.
Reconnect all harness connectors.
Turn the disconnect switch and the key start switch to the ON position.
Clear all inactive diagnostic codes.
Operate the machine.
Stop the machine.
Check if the diagnostic code for the solenoid valve is present. Expected Result:The diagnostic code for the solenoid valve is NO longer present.Results:
YES - The diagnostic code is NOT present. The diagnostic code does not exist at this time. The initial diagnostic code was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.STOP
NO - The diagnostic code has not been corrected.Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. Also, recheck if the diagnostic code is active. If the cause of the diagnostic code is not found, replace the ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".STOP