HOUSING-FRONT 3N6911 - Caterpillar

Illustration 1 g03815849
Connections of the Cab Blower Speed (HVAC ) ControlThis diagnostic code is recorded when the Implement ECM reads the input signal for the HVAC Blower Speed Control and the voltage is below normal.If the voltage of the sensor input circuit is less than 0.25 VDC, an FMI 04 diagnostic code will be activated.The possible causes of this diagnostic code are listed below:
The signal circuit shorted to ground.
The HVAC panel has failed.
The ECM has failed. This condition is unlikely. Note: Before performing this procedure, inspect the harness connectors that are involved in the circuit.
Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, that all connections are secure and that all connections are in good condition.
If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing this procedure.Note: The following test procedure may create other diagnostic codes. Ignore these created diagnostic codes and clear the diagnostic codes when the original diagnostic code has been corrected. System Response:
The Auto Blower Control feature will not work properly.
The blower speed cannot be adjusted.Test Step 1. CHECK THE HVAC PANEL
Turn the disconnect switch and the key start switch to the ON position.
Ensure that the diagnostic code is active.
Observe the status of the diagnostic code. Disconnect the HVAC panel from the machine harness.Expected Result:The CID 2811 FMI 4 diagnostic code changes to a CID 2811 FMI 3 diagnostic code when the panel is disconnected from the machine harness.Results:
YES - The CID 2811 FMI 4 diagnostic code changes to a CID 2811 FMI 3 diagnostic code when the panel is disconnected. The panel has failed.Repair: The panel is causing the problem. Replace the HVAC panel.STOP
NO - Disconnecting the panel from the machine harness did not change the status for the active diagnostic code. The CID 2811 FMI 04 diagnostic code is still active. The panel is not causing the problem. Proceed to Test Step 2.Test Step 2. CHECK THE SIGNAL CIRCUIT FOR A SHORTThe panel remains disconnected from the machine harness.
Turn the key start switch and the disconnect switch to the OFF position.
Disconnect the machine harness connector J1 from the ECM.
At the machine harness connector for the ECM, measure the resistance from the signal contact J1-37 (wire E529-YL) to frame ground. Measure the resistance from the signal contact J1-37 (wire E529-YL) to all of the contacts that are used in the machine harness connectors for the ECM.Expected Result:Each resistance measurement is greater than 5000 ohms.Results:
OK - Each resistance measurement is greater than 5000 ohms. The machine harness is correct. Proceed to Test Step 3.
NOT OK - One or more resistance measurements are less than 5000 ohms. There is a short in the machine harness.Repair: The short is between signal wire E529-YL and the circuit with the low resistance measurement. Repair or replace the machine harness.STOPTest Step 3. CHECK THE OPERATION OF THE ECMThe key start switch and the disconnect switch